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  • Trying to write a std::iterator : Compilation error

    - by Naveen
    I am trying to write an std::iterator for the CArray<Type,ArgType> MFC class. This is what I have done till now: template <class Type, class ArgType> class CArrayIterator : public std::iterator<std::random_access_iterator_tag, ArgType> { public: CArrayIterator(CArray<Type,ArgType>& array_in, int index_in = 0) : m_pArray(&array_in), m_index(index_in) { } void operator++() { ++m_index; } void operator++(int) { ++m_index; } void operator--() { --m_index; } void operator--(int) { --m_index; } void operator+=(int n) { m_index += n; } void operator-=(int n) { m_index -= n; } typename ArgType operator*() const{ return m_pArray->GetAt(m_index); } typename ArgType operator->() const { return m_pArray->GetAt(m_index); } bool operator==(const CArrayIterator& other) const { return m_pArray == other.m_pArray && m_index == other.m_index; } bool operator!=(const CArrayIterator& other) const { return ! (operator==(other)); } private: CArray<Type,ArgType>* m_pArray; int m_index; }; I also provided two helper functions to create the iterators like this: template<class Type, class ArgType> CArrayIterator<Type,ArgType> make_begin(CArray<Type,ArgType>& array_in) { return CArrayIterator<Type,ArgType>(array_in, 0); } template<class Type, class ArgType> CArrayIterator<Type,ArgType> make_end(CArray<Type,ArgType>& array_in) { return CArrayIterator<Type,ArgType>(array_in, array_in.GetSize()); } To test the code, I wrote a simple class A and tried to use it like this: class A { public: A(int n): m_i(n) { } int get() const { return m_i; } private: int m_i; }; struct Test { void operator()(A* p) { std::cout<<p->get()<<"\n"; } }; int main(int argc, char **argv) { CArray<A*, A*> b; b.Add(new A(10)); b.Add(new A(20)); std::for_each(make_begin(b), make_end(b), Test()); return 0; } But when I compile this code, I get the following error: Error 4 error C2784: 'bool std::operator <(const std::_Tree<_Traits &,const std::_Tree<_Traits &)' : could not deduce template argument for 'const std::_Tree<_Traits &' from 'CArrayIterator' C:\Program Files\Microsoft Visual Studio 9.0\VC\include\xutility 1564 Vs8Console Can anybody throw some light on what I am doing wrong and how it can be corrected? I am using VC9 compiler if it matters.

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  • C++ -- Why should we use operator -> to access member functions of a SmartPtr?

    - by q0987
    Hello all, The question is given in the last two lines of code. template<class T> // template class for smart class SmartPtr { // pointers-to-T objects public: SmartPtr(T* realPtr = 0); T* operator->() const; T& operator*() const; T* Detach( void ) { T* pData = pointee; pointee = NULL; return pData; } private: T *pointee; ... }; class TestClass {} SmartPtr<TestClass> sPtr(new TestClass); TestClass* ptrA = sPtr->Detach(); // why I always see people use this method to access member functions of a Smart pointer. We can use sPtr-> b/c we have defined operator->() in SmartPtr. TestClass* ptrB = sPtr.Detach(); // Question: Is this a valid C++ way? If not, why? Thank you

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  • Intent and OnActivityResult causing Activity to get restart Actuomatically : Require to solve this issues

    - by Parth Dani
    i am having 20 imageview and i am having 20 button for them when i click any 1 button it gives me option to select image from gallery or camera when i select any option for example galley it will take me to the gallery and let me select image from their and let me display those images on my imageview for respective button now the problem is sometimes when i do the whole above process my activity is getting restart actuomatically and all the image which were first selected get vanished from their imageview For Refernce my code is as follow: @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.new_upload); // **************Code to get Road worthy number and VIN number value in // Shared Preference starts here************************ SharedPreferences myPrefs1 = this.getSharedPreferences("myPrefs", MODE_WORLD_READABLE); roadworthynumber = myPrefs1.getString(MY_ROADWORTHY, "Road Worthy Number"); vinnumber = myPrefs1.getString(MY_VIN, "VIN Number"); // **************Code to get Road worthy number and VIN number value in // Shared Preference ends here************************ // **************Code to create Directory AUSRWC starts // here************************ if (android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) { cacheDir = new File(Environment.getExternalStorageDirectory() + File.separator + "AUSRWC" + File.separator); cacheDir.mkdirs(); } // **************Code to Create Directory AUSRWC ends // here************************ // *****************Assigning Button variable their Id declare in XML // file starts here***************** new_select1 = (Button) findViewById(R.id.new_select1); new_select2 = (Button) findViewById(R.id.new_select2); new_select3 = (Button) findViewById(R.id.new_select3); new_select4 = (Button) findViewById(R.id.new_select4); new_select5 = (Button) findViewById(R.id.new_select5); new_select6 = (Button) findViewById(R.id.new_select6); new_select7 = (Button) findViewById(R.id.new_select7); new_select8 = (Button) findViewById(R.id.new_select8); new_select9 = (Button) findViewById(R.id.new_select9); new_select10 = (Button) findViewById(R.id.new_select10); new_select11 = (Button) findViewById(R.id.new_select11); new_select12 = (Button) findViewById(R.id.new_select12); new_select13 = (Button) findViewById(R.id.new_select13); new_select14 = (Button) findViewById(R.id.new_select14); new_select15 = (Button) findViewById(R.id.new_select15); new_select16 = (Button) findViewById(R.id.new_select16); new_select17 = (Button) findViewById(R.id.new_select17); new_select18 = (Button) findViewById(R.id.new_select18); new_select19 = (Button) findViewById(R.id.new_select19); new_select20 = (Button) findViewById(R.id.new_select20); // *****************Assigning Button variable their Id declare in XML // file ends here***************** // *****************Assigning Image variable their Id declare in XML // file starts here***************** new_selectimage1 = (ImageView) findViewById(R.id.new_selectImage1); new_selectimage2 = (ImageView) findViewById(R.id.new_selectImage2); new_selectimage3 = (ImageView) findViewById(R.id.new_selectImage3); new_selectimage4 = (ImageView) findViewById(R.id.new_selectImage4); new_selectimage5 = (ImageView) findViewById(R.id.new_selectImage5); new_selectimage6 = (ImageView) findViewById(R.id.new_selectImage6); new_selectimage7 = (ImageView) findViewById(R.id.new_selectImage7); new_selectimage8 = (ImageView) findViewById(R.id.new_selectImage8); new_selectimage9 = (ImageView) findViewById(R.id.new_selectImage9); new_selectimage10 = (ImageView) findViewById(R.id.new_selectImage10); new_selectimage11 = (ImageView) findViewById(R.id.new_selectImage11); new_selectimage12 = (ImageView) findViewById(R.id.new_selectImage12); new_selectimage13 = (ImageView) findViewById(R.id.new_selectImage13); new_selectimage14 = (ImageView) findViewById(R.id.new_selectImage14); new_selectimage15 = (ImageView) findViewById(R.id.new_selectImage15); new_selectimage16 = (ImageView) findViewById(R.id.new_selectImage16); new_selectimage17 = (ImageView) findViewById(R.id.new_selectImage17); new_selectimage18 = (ImageView) findViewById(R.id.new_selectImage18); new_selectimage19 = (ImageView) findViewById(R.id.new_selectImage19); new_selectimage20 = (ImageView) findViewById(R.id.new_selectImage20); // ****Assigning Image variable their Id declare in XML file ends // here***************** // **************Creating Dialog to give option to user to new_select // image from gallery or from camera starts here**************** final String[] items = new String[] { "From Camera", "From Gallery" }; ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.select_dialog_item, items); AlertDialog.Builder builder = new AlertDialog.Builder(this); builder.setTitle("select Image"); builder.setAdapter(adapter, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int item) { if (item == 0) { if (android.os.Environment.getExternalStorageState() .equals(android.os.Environment.MEDIA_MOUNTED)) { Intent intent = new Intent( MediaStore.ACTION_IMAGE_CAPTURE); File file = new File(Environment .getExternalStorageDirectory(), "/AUSRWC/picture" + ".jpg"); mImageCaptureUri = Uri.fromFile(file); try { Toast.makeText(getBaseContext(), "Click Image", Toast.LENGTH_SHORT).show(); intent.putExtra( android.provider.MediaStore.EXTRA_OUTPUT, mImageCaptureUri); intent.putExtra("return-data", true); startActivityForResult(intent, PICK_FROM_CAMERA); } catch (Exception e) { e.printStackTrace(); } } else { Toast.makeText(getBaseContext(), "Please insert SdCard First", Toast.LENGTH_SHORT).show(); } dialog.cancel(); } else { Intent intent = new Intent(); Toast.makeText(getBaseContext(), "Select Image", Toast.LENGTH_SHORT).show(); intent.setType("image/*"); intent.setAction(Intent.ACTION_GET_CONTENT); startActivityForResult(Intent.createChooser(intent, "Complete action using"), PICK_FROM_FILE); } } }); dialog = builder.create(); // **************Creating Dialog to give option to user to new_select // image from gallery or from camera ends here**************** final Animation animAlpha = AnimationUtils.loadAnimation(this, R.anim.anim_alpha); // Animation Code for displaying Button // Clicked. // ********************Image 1 button code starts // here******************************* if (android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) { new_select1.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { v.startAnimation(animAlpha); buttonpressed = 1; dialog.show(); } }); } else { Toast.makeText(getBaseContext(), "Please insert SdCard First", Toast.LENGTH_SHORT).show(); } // ********************Image 1 button code ends // here******************************* // ********************Image 2 button code starts // here******************************* if (android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) { new_select2.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { v.startAnimation(animAlpha); buttonpressed = 2; dialog.show(); } }); } else { Toast.makeText(getBaseContext(), "Please insert SdCard First", Toast.LENGTH_SHORT).show(); } // ********************Image 2 button code ends // here******************************* // ********************Image 3 button code starts // here******************************* if (android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) { new_select3.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { v.startAnimation(animAlpha); buttonpressed = 3; dialog.show(); } }); } else { Toast.makeText(getBaseContext(), "Please insert SdCard First", Toast.LENGTH_SHORT).show(); } // ********************Image 3 button code ends // here******************************* // ********************Image 4 button code starts // here******************************* if (android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) { new_select4.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { v.startAnimation(animAlpha); buttonpressed = 4; dialog.show(); } }); } else { Toast.makeText(getBaseContext(), "Please insert SdCard First", Toast.LENGTH_SHORT).show(); } // ********************Image 4 button code ends // here******************************* // ********************Image 5 button code starts // here******************************* if (android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) { new_select5.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { v.startAnimation(animAlpha); buttonpressed = 5; dialog.show(); } }); } else { Toast.makeText(getBaseContext(), "Please insert SdCard First", Toast.LENGTH_SHORT).show(); } // ********************Image 5 button code ends // here******************************* // ********************Image 6 button code starts // here******************************* if (android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) { new_select6.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { v.startAnimation(animAlpha); buttonpressed = 6; dialog.show(); } }); } else { Toast.makeText(getBaseContext(), "Please insert SdCard First", Toast.LENGTH_SHORT).show(); } // ********************Image 6 button code ends // here******************************* // ********************Image 7 button code starts // here******************************* if (android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) { new_select7.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { v.startAnimation(animAlpha); buttonpressed = 7; dialog.show(); } }); } else { Toast.makeText(getBaseContext(), "Please insert SdCard First", Toast.LENGTH_SHORT).show(); } // ********************Image 7 button code ends // here******************************* // ********************Image 8 button code starts // here******************************* if (android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) { new_select8.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { v.startAnimation(animAlpha); buttonpressed = 8; dialog.show(); } }); } else { Toast.makeText(getBaseContext(), "Please insert SdCard First", Toast.LENGTH_SHORT).show(); } // ********************Image 8 button code ends // here******************************* // ********************Image 9 button code starts // here******************************* if (android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) { new_select9.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { v.startAnimation(animAlpha); buttonpressed = 9; dialog.show(); } }); } else { Toast.makeText(getBaseContext(), "Please insert SdCard First", Toast.LENGTH_SHORT).show(); } // ********************Image 9 button code ends // here******************************* // ********************Image 10 button code starts // here******************************* if (android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) { new_select10.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { v.startAnimation(animAlpha); buttonpressed = 10; dialog.show(); } }); } else { Toast.makeText(getBaseContext(), "Please insert SdCard First", Toast.LENGTH_SHORT).show(); } // ********************Image 10 button code ends // here******************************* // ********************Image 11 button code starts // here******************************* if (android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) { new_select11.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { v.startAnimation(animAlpha); buttonpressed = 11; dialog.show(); } }); } else { Toast.makeText(getBaseContext(), "Please insert SdCard First", Toast.LENGTH_SHORT).show(); } // ********************Image 11 button code ends // here******************************* // ********************Image 12 button code starts // here******************************* if (android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) { new_select12.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { v.startAnimation(animAlpha); buttonpressed = 12; dialog.show(); } }); } else { Toast.makeText(getBaseContext(), "Please insert SdCard First", Toast.LENGTH_SHORT).show(); } // ********************Image 12 button code ends // here******************************* // ********************Image 13 button code starts // here******************************* if (android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) { new_select13.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { v.startAnimation(animAlpha); buttonpressed = 13; dialog.show(); } }); } else { Toast.makeText(getBaseContext(), "Please insert SdCard First", Toast.LENGTH_SHORT).show(); } // ********************Image 13 button code ends // here******************************* // ********************Image 14 button code starts // here******************************* if (android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) { new_select14.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { v.startAnimation(animAlpha); buttonpressed = 14; dialog.show(); } }); } else { Toast.makeText(getBaseContext(), "Please insert SdCard First", Toast.LENGTH_SHORT).show(); } // ********************Image 14 button code ends // here******************************* // ********************Image 15 button code starts // here******************************* if (android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) { new_select15.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { v.startAnimation(animAlpha); buttonpressed = 15; dialog.show(); } }); } else { Toast.makeText(getBaseContext(), "Please insert SdCard First", Toast.LENGTH_SHORT).show(); } // ********************Image 15 button code ends // here******************************* // ********************Image 16 button code starts // here******************************* if (android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) { new_select16.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { v.startAnimation(animAlpha); buttonpressed = 16; dialog.show(); } }); } else { Toast.makeText(getBaseContext(), "Please insert SdCard First", Toast.LENGTH_SHORT).show(); } // ********************Image 16 button code ends // here******************************* // ********************Image 17 button code starts // here******************************* if (android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) { new_select17.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { v.startAnimation(animAlpha); buttonpressed = 17; dialog.show(); } }); } else { Toast.makeText(getBaseContext(), "Please insert SdCard First", Toast.LENGTH_SHORT).show(); } // ********************Image 17 button code ends // here******************************* // ********************Image 18 button code starts // here******************************* if (android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) { new_select18.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { v.startAnimation(animAlpha); buttonpressed = 18; dialog.show(); } }); } else { Toast.makeText(getBaseContext(), "Please insert SdCard First", Toast.LENGTH_SHORT).show(); } // ********************Image 18 button code ends // here******************************* // ********************Image 19 button code starts // here******************************* if (android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) { new_select19.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { v.startAnimation(animAlpha); buttonpressed = 19; dialog.show(); } }); } else { Toast.makeText(getBaseContext(), "Please insert SdCard First", Toast.LENGTH_SHORT).show(); } // ********************Image 19 button code ends // here******************************* // ********************Image 20 button code starts // here******************************* if (android.os.Environment.getExternalStorageState().equals( android.os.Environment.MEDIA_MOUNTED)) { new_select20.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { v.startAnimation(animAlpha); buttonpressed = 20; dialog.show(); } }); } else { Toast.makeText(getBaseContext(), "Please insert SdCard First", Toast.LENGTH_SHORT).show(); } // ********************Image 20 button code ends // here******************************* } // *************************When Back Button is Pressed code begins // here************************************* @Override public void onBackPressed() { Toast.makeText(new_upload.this, "Sorry You are not allowed to go back", Toast.LENGTH_SHORT).show(); return; } // *************************When Back Button is Pressed code ends // here************************************* // ***********************To get Path of new_selected Image code starts // here************************************ public String getRealPathFromURI(Uri contentUri) { String[] proj = { MediaStore.Images.Media.DATA }; Cursor cursor = managedQuery(contentUri, proj, null, null, null); if (cursor == null) return null; int column_index = cursor .getColumnIndexOrThrow(MediaStore.Images.Media.DATA); cursor.moveToFirst(); return cursor.getString(column_index); } // ***********************To get Path of new_selected Image code ends // here************************************ // **********************Picture obtained from the camera or from gallery // code starts here************** @Override protected void onActivityResult(int requestCode, int resultCode, Intent data) { //path = ""; Log.e("","requestCode="+requestCode); switch (requestCode){ case PICK_FROM_FILE: if (resultCode == Activity.RESULT_OK) { mImageCaptureUri = data.getData(); path = getRealPathFromURI(mImageCaptureUri); // from Gallery Log.e("", "Imagepath from gallery=" + path); if (path == null) path = mImageCaptureUri.getPath(); // from File Manager if (path != null) { dialog1 = ProgressDialog.show(new_upload.this, "", "Processing Please wait...", true); new ImageDisplayTask().execute(); } } break; case PICK_FROM_CAMERA: if (resultCode == Activity.RESULT_OK) { try { path = mImageCaptureUri.getPath(); Log.e("", "Imagepath from Camera =" + path); // bitmap = BitmapFactory.decodeFile(path); } catch (Exception e) { e.printStackTrace(); } if (path != null) { dialog1 = ProgressDialog.show(new_upload.this, "", "Processing Please wait...", true); //new ImageDisplayTask1().execute(); new ImageDisplayTask().execute(); } } break; default: } } // ********************Picture obtained from the camera or from gallery code // ends here********************************************* // ******************Image Display on Button when new_selected from gallery // Ashynch Code starts here******************************** class ImageDisplayTask extends AsyncTask<Void, Void, String> { @Override protected String doInBackground(Void... unsued) { Bitmap src = BitmapFactory.decodeFile(path); Bitmap dest = Bitmap.createBitmap(src.getWidth(), src.getHeight(), Bitmap.Config.ARGB_8888); //Bitmap dest = Bitmap.createScaledBitmap(src, src.getWidth(),src.getHeight(), true); SimpleDateFormat sdf = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss"); String dateTime = sdf.format(Calendar.getInstance().getTime()); // reading local `` String timestamp = dateTime + " " + roadworthynumber; SimpleDateFormat sdf1 = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss"); String dateTime1 = sdf1.format(Calendar.getInstance().getTime()); Imagename = dateTime1.toString().trim().replaceAll(":", "") .replaceAll("-", "").replaceAll(" ", "") + roadworthynumber + ".jpg"; Canvas cs = new Canvas(dest); Paint tPaint = new Paint(); tPaint.setTextSize(100); tPaint.setTypeface(Typeface.SERIF); tPaint.setColor(Color.RED); tPaint.setStyle(Style.FILL); cs.drawBitmap(src, 0f, 0f, null); float height = tPaint.measureText("yY"); cs.drawText(timestamp, 5f, src.getHeight() - height + 5f, tPaint); try { dest.compress(Bitmap.CompressFormat.JPEG, 70, new FileOutputStream(new File(cacheDir, Imagename))); dest.recycle(); src.recycle(); } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } return null; } @Override protected void onProgressUpdate(Void... unsued) { } @Override protected void onPostExecute(String serverresponse) { String error = "noerror"; Display currentDisplay = getWindowManager().getDefaultDisplay(); int dw = currentDisplay.getWidth(); int dh = currentDisplay.getHeight() - 100; Log.e("", "width= " + dw + " Height= " + dh); try { BitmapFactory.Options bmpFactoryOptions = new BitmapFactory.Options(); bmpFactoryOptions.inJustDecodeBounds = true; Bitmap bmp = BitmapFactory.decodeFile( Environment.getExternalStorageDirectory() + "/AUSRWC/" + Imagename, bmpFactoryOptions); int heightRatio = (int) Math.ceil(bmpFactoryOptions.outHeight / (float) dh); int widthRatio = (int) Math.ceil(bmpFactoryOptions.outWidth / (float) dw); if (heightRatio > 1 && widthRatio > 1) { if (heightRatio > widthRatio) { bmpFactoryOptions.inSampleSize = heightRatio; } else { bmpFactoryOptions.inSampleSize = widthRatio; } } bmpFactoryOptions.inJustDecodeBounds = false; bmp = BitmapFactory.decodeFile( Environment.getExternalStorageDirectory() + "/AUSRWC/" + Imagename, bmpFactoryOptions); if (buttonpressed == 1) { new_selectimage1.setImageBitmap(bmp); //Image set on ImageView } else if (buttonpressed == 2) { new_selectimage2.setImageBitmap(bmp);//Image set on ImageView } else if (buttonpressed == 3) { new_selectimage3.setImageBitmap(bmp);//Image set on ImageView } else if (buttonpressed == 4) { new_selectimage4.setImageBitmap(bmp);//Image set on ImageView } else if (buttonpressed == 5) { new_selectimage5.setImageBitmap(bmp);//Image set on ImageView } else if (buttonpressed == 6) { new_selectimage6.setImageBitmap(bmp);//Image set on ImageView } else if (buttonpressed == 7) { new_selectimage7.setImageBitmap(bmp);//Image set on ImageView } else if (buttonpressed == 8) { new_selectimage8.setImageBitmap(bmp);//Image set on ImageView } else if (buttonpressed == 9) { new_selectimage9.setImageBitmap(bmp);//Image set on ImageView } else if (buttonpressed == 10) { new_selectimage10.setImageBitmap(bmp); } else if (buttonpressed == 11) { new_selectimage11.setImageBitmap(bmp); } else if (buttonpressed == 12) { new_selectimage12.setImageBitmap(bmp); } else if (buttonpressed == 13) { new_selectimage13.setImageBitmap(bmp); } else if (buttonpressed == 14) { new_selectimage14.setImageBitmap(bmp); } else if (buttonpressed == 15) { new_selectimage15.setImageBitmap(bmp); } else if (buttonpressed == 16) { new_selectimage16.setImageBitmap(bmp); } else if (buttonpressed == 17) { new_selectimage17.setImageBitmap(bmp); } else if (buttonpressed == 18) { new_selectimage18.setImageBitmap(bmp); } else if (buttonpressed == 19) { new_selectimage19.setImageBitmap(bmp); } else if (buttonpressed == 20) { new_selectimage20.setImageBitmap(bmp); } } catch (Exc

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  • Example of when the culture parameter of string.Equals (c#) actually makes a difference?

    - by dru-zod
    I don’t fully understand the second parameter of string.Equals, and this is because I can’t find any examples of when it would actually make a difference. For example, the example given here is the same, regardless of the value of the second parameter (aside from IgnoreCase): http://msdn.microsoft.com/en-us/library/c64xh8f9.aspx I am just talking about the values StringComparison.CurrentCulture, InvariantCulture, or Ordinal. I can understand the difference between these and their IgnoreCase equivalents.

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  • infix operation to postfix using stacks

    - by Chris De La O
    We are writing a program that needs to convert an infix operation (4 5/3) to postfix (4 5 3 / ) using stacks. however my convert to postfix does not work as it doesnt not output the postFix array that is supposed to store the conversion from infix notation to postfix notation. here is the code for the convertToPostix fuction. //converts infix expression to postfix expression void ArithmeticExpression::convertToPostfix(char *const inFix, char *const postFix) { //create a stack2 object named cow Stack2<char> cow; cout<<postFix; char thing = '('; //push a left parenthesis onto the stack cow.push(thing); //append a right parenthesis to the end of inFix array strcat(inFix, ")"); int i = 0;//declare an int that will control posFix position //if the stack is not empty if (!cow.isEmpty()) { //loop to run until the last character in inFix array for (int x = 0; inFix[x]!= '\0'; x++ ) { //if the inFix element is a digit if (isdigit(inFix[x])) { postFix[i]=inFix[x];//it is assigned to the next element in postFix array i++;//move on to next element in postFix } //if the inFix element is a left parenthesis else if (inFix[x]=='(') { cow.push(inFix[x]);//push it unto the stack } //if the inFix element is an operator else if (isOperator(inFix[x])) { char oper2 = inFix[x];//char variable holds inFix operator if (isOperator(cow.stackTop()))//if the top node in the stack is an operator { while (isOperator(cow.stackTop()))//and while the top node in the stack is an operator { char oper1 = cow.stackTop();//char variable holds node operator if(precedence( oper1, oper2))//if the node operator has higher presedence than node operator { postFix[i] = cow.pop();//we pop such operator and insert it in postFix array's next element cow.push(inFix[x]);//and push inFix operator unto the stack i++;//move to the next element in posFix } } } //if the top node is not an operator //we push the current inFix operator unto the top of the stack else cow.push(inFix[x]); } //if the inFix element is a right parenthesis else if (inFix[x]==')') { //we pop everything in the stack and insert it in postFix //until we arrive at a left paranthesis while (cow.stackTop()!='(') { postFix[i] = cow.pop(); i++; } //we then pop and discard left parenthesis cow.pop(); } } postFix[i]='\0'; //print !!postFix array!! (not stack) print();//code for this is just cout<<postFix; }

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  • Java Compiler Creation Help..Please

    - by Brian
    I need some help with my code here...What we are trying to do is make a compiler that will read a file containing Machine Code and converting it to 100 lines of 4 bits example: this code is the machine code being converting to opcode and operands. I need some help please.. thanks 799 798 198 499 1008 1108 899 909 898 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Everything compiles but when I go and run my Test.java I get the following OutPut: Exception in thread "main" java.util.NoSuchElementException: No line found at java.util.Scanner.nextLine(Scanner.java:1516) at Compiler.FirstPass(Compiler.java:22) at Compiler.compile(Compiler.java:11) at Test.main(Test.java:5) Here is my class Compiler: import java.io.*; import java.io.DataOutputStream; import java.util.NoSuchElementException; import java.util.Scanner; class Compiler{ private int lc = 0; private int dc = 99; public void compile(String filename) { SymbolList symbolTable = FirstPass(filename); SecondPass(symbolTable, filename); } public SymbolList FirstPass(String filename) { File file = new File(filename); SymbolList temp = new SymbolList(); int dc = 99; int lc = 0; try{ Scanner scan = new Scanner(file); String line = scan.nextLine(); String[] linearray = line.split(" "); while(line!=null){ if(!linearray[0].equals("REM")){ if(!this.isInstruction(linearray[0])){ linearray[0]=removeColon(linearray[0]); if(this.isInstruction(linearray[1])){ temp.add(new Symbol(linearray[0], lc, null)); lc++; } else { temp.add(new Symbol(linearray[0], dc, Integer.valueOf((linearr\ ay[2])))); dc--; } } else { if(!linearray[0].equals("REM")) lc++; } } try{ line = scan.nextLine(); } catch(NoSuchElementException e){ line=null; break; } linearray = line.split(" "); } } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } return temp; } public String makeFilename(String filename) { return filename + ".ex"; } public String removeColon(String str) { if(str.charAt(str.length()-1) == ':'){ return str.substring(0, str.length()-1); } else { return str; } } public void SecondPass(SymbolList symbolTable, String filename){ try { int dc = 99; //Open file for reading File file = new File(filename); Scanner scan = new Scanner(file); //Make filename of new executable file String newfile = makeFilename(filename); //Open Output Stream for writing new file. FileOutputStream os = new FileOutputStream(filename); DataOutputStream dos = new DataOutputStream(os); //Read First line. Split line by Spaces into linearray. String line = scan.nextLine(); String[] linearray = line.split(" "); while(scan.hasNextLine()){ if(!linearray[0].equals("REM")){ int inst=0, opcode, loc; if(isInstruction(linearray[0])){ opcode = getOpcode(linearray[0]); loc = symbolTable.searchName(linearray[1]).getMemloc(); inst = (opcode*100)+loc; } else if(!isInstruction(linearray[0])){ if(isInstruction(linearray[1])){ opcode = getOpcode(linearray[1]); if(linearray[1].equals("STOP")) inst=0000; else { loc = symbolTable.searchName(linearray[2]).getMemloc(); inst = (opcode*100)+loc; } } if(linearray[1].equals("DC")) dc--; } System.out.println(inst); dos.writeInt(inst); linearray = line.split(" "); } if(scan.hasNextLine()) { line = scan.nextLine(); } } scan.close(); for(int i = lc; i <= dc; i++) { dos.writeInt(0); } for(int i = dc+1; i<100; i++){ dos.writeInt(symbolTable.searchLocation(i).getValue()); if(i!=99) dos.writeInt(0); } dos.close(); os.close(); } catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); } } public int getOpcode(String inst){ int toreturn = -1; if(isInstruction(inst)){ if(inst.equals("STOP")) toreturn=0; if(inst.equals("LD")) toreturn=1; if(inst.equals("STO")) toreturn=2; if(inst.equals("ADD")) toreturn=3; if(inst.equals("SUB")) toreturn=4; if(inst.equals("MPY")) toreturn=5; if(inst.equals("DIV")) toreturn=6; if(inst.equals("IN")) toreturn=7; if(inst.equals("OUT")) toreturn=8; if(inst.equals("B")) toreturn=9; if(inst.equals("BGTR")) toreturn=10; if(inst.equals("BZ")) toreturn=11; return toreturn; } else { return -1; } } public boolean isInstruction(String totest){ boolean toreturn = false; String[] labels = {"IN", "LD", "SUB", "BGTR", "BZ", "OUT", "B", "STO", "STOP", "AD\ D", "MTY", "DIV"}; for(int i = 0; i < 12; i++){ if(totest.equals(labels[i])) toreturn = true; } return toreturn; } } And here is my class Computer: import java.io.*; import java.util.NoSuchElementException; import java.util.Scanner; class Computer{ private Cpu cpu; private Input in; private OutPut out; private Memory mem; public Computer() throws IOException { Memory mem = new Memory(100); Input in = new Input(); OutPut out = new OutPut(); Cpu cpu = new Cpu(); System.out.println(in.getInt()); } public void run() throws IOException { cpu.reset(); cpu.setMDR(mem.read(cpu.getMAR())); cpu.fetch2(); while (!cpu.stop()) { cpu.decode(); if (cpu.OutFlag()) OutPut.display(mem.read(cpu.getMAR())); if (cpu.InFlag()) mem.write(cpu.getMDR(),in.getInt()); if (cpu.StoreFlag()) { mem.write(cpu.getMAR(),in.getInt()); cpu.getMDR(); } else { cpu.setMDR(mem.read(cpu.getMAR())); cpu.execute(); cpu.fetch(); cpu.setMDR(mem.read(cpu.getMAR())); cpu.fetch2(); } } } public void load() { mem.loadMemory(); } } Here is my Memory class: import java.io.*; import java.util.NoSuchElementException; import java.util.Scanner; class Memory{ private MemEl[] memArray; private int size; private int[] mem; public Memory(int s) {size = s; memArray = new MemEl[s]; for(int i = 0; i < s; i++) memArray[i] = new MemEl(); } public void write (int loc,int val) {if (loc >=0 && loc < size) memArray[loc].write(val); else System.out.println("Index Not in Domain"); } public int read (int loc) {return memArray[loc].read(); } public void dump() { for(int i = 0; i < size; i++) if(i%1 == 0) System.out.println(memArray[i].read()); else System.out.print(memArray[i].read()); } public void writeTo(int location, int value) { mem[location] = value; } public int readFrom(int location) { return mem[location]; } public int size() { return mem.length; } public void loadMemory() { this.write(0, 799); this.write(1, 798); this.write(2, 198); this.write(3, 499); this.write(4, 1008); this.write(5, 1108); this.write(6, 899); this.write(7, 909); this.write(8, 898); this.write(9, 0000); } public void loadFromFile(String filename){ try { FileReader fr = new FileReader(filename); BufferedReader br = new BufferedReader(fr); String read=null; int towrite=0; int l=0; do{ try{ read=br.readLine(); towrite = Integer.parseInt(read); }catch(Exception e){ } this.write(l, towrite); l++; }while(l<100); }catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); } } } Here is my Test class: public class Test{ public static void main(String[] args) throws java.io.IOException { Compiler compiler = new Compiler(); compiler.compile("program.txt"); } }

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  • Java Appending a character to a textarea

    - by adam08
    I'm looking to appends a character to a textarea in. I have a simple GUI designed to look like like a mobile phone and I want to be able to click on one of the buttons and update the textarea with that character. If I click another button, I want to be able to append that character to the first. How do I do this? Obviously right now it is just setting the character for that button in the textarea and will be replaced when another button is clicked. public void actionPerformed(ActionEvent e) { String source = e.getActionCommand(); if (source.equals("1")) { TextArea.setText("1"); } else if (source.equals("2abc")) { TextArea.setText("a"); } else if (source.equals("3def")) { TextArea.setText("e"); } else if (source.equals("4ghi")) { TextArea.setText("i"); } else if (source.equals("5jkl")) { TextArea.setText("k"); } else if (source.equals("6mno")) { TextArea.setText("o"); } else if (source.equals("7pqrs")) { TextArea.setText("s"); } else if (source.equals("8tuv")) { TextArea.setText("t"); } else if (source.equals("9wxyz")) { TextArea.setText("x"); }

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  • What is the justification for Python's power operator associating to the right?

    - by Pieter Müller
    I am writing code to parse mathematical expression strings, and noticed that the order in which chained power operators are evaluated in Python differs from the order in Excel. From http://docs.python.org/reference/expressions.html: "Thus, in an unparenthesized sequence of power and unary operators, the operators are evaluated from right to left (this does not constrain the evaluation order for the operands): -1*2 results in -1."* This means that, in Python: 2**2**3 is evaluated as 2**(2**3) = 2**8 = 256 In Excel, it works the other way around: 2^2^3 is evaluated as (2^2)^3 = 4^3 = 64 I now have to choose an implementation for my own parser. The Excel order is easier to implement, as it mirrors the evaluation order of multiplication. I asked some people around the office what their gut feel was for the evaluation of 2^2^3 and got mixed responses. Does anybody know of any good reasons or conciderations in favour of the Python implementation? And if you don't have an answer, please comment with the result you get from gut feel - 64 or 256?

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  • Stairway to T-SQL DML Level 8: Using the ROLLUP, CUBE and GROUPING SET operator in a GROUP BY Clause

    In this article I will be expanding on my discussion of the GROUP BY clause by exploring the ROLLUP, CUBE and GROUPING SETS operators. These additional GROUP BY operators make it is easy to have SQL Server create subtotals, grand totals, a superset of subtotals, as well as multiple aggregate groupings in a single SELECT statement. Local evaluation repository makes trying SQL Source Control simpleThe evaluation repository makes it easy to try SQL Source Control. Get started with the 28-day free trial.

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  • Trouble calling a method from an external class

    - by Bradley Hobbs
    Here is my employee database program: import java.util.*; import java.io.*; import java.io.File; import java.io.FileReader; import java.util.ArrayList; public class P { //Instance Variables private static String empName; private static String wage; private static double wages; private static double salary; private static double numHours; private static double increase; // static ArrayList<String> ARempName = new ArrayList<String>(); // static ArrayList<Double> ARwages = new ArrayList<Double>(); // static ArrayList<Double> ARsalary = new ArrayList<Double>(); static ArrayList<Employee> emp = new ArrayList<Employee>(); public static void main(String[] args) throws Exception { clearScreen(); printMenu(); question(); exit(); } public static void printArrayList(ArrayList<Employee> emp) { for (int i = 0; i < emp.size(); i++){ System.out.println(emp.get(i)); } } public static void clearScreen() { System.out.println("\u001b[H\u001b[2J"); } private static void exit() { System.exit(0); } private static void printMenu() { System.out.println("\t------------------------------------"); System.out.println("\t|Commands: n - New employee |"); System.out.println("\t| c - Compute paychecks |"); System.out.println("\t| r - Raise wages |"); System.out.println("\t| p - Print records |"); System.out.println("\t| d - Download data |"); System.out.println("\t| u - Upload data |"); System.out.println("\t| q - Quit |"); System.out.println("\t------------------------------------"); System.out.println(""); } public static void question() { System.out.print("Enter command: "); Scanner q = new Scanner(System.in); String input = q.nextLine(); input.replaceAll("\\s","").toLowerCase(); boolean valid = (input.equals("n") || input.equals("c") || input.equals("r") || input.equals("p") || input.equals("d") || input.equals("u") || input.equals("q")); if (!valid){ System.out.println("Command was not recognized; please try again."); printMenu(); question(); } else if (input.equals("n")){ System.out.print("Enter the name of new employee: "); Scanner stdin = new Scanner(System.in); empName = stdin.nextLine(); System.out.print("Hourly (h) or salaried (s): "); Scanner stdin2 = new Scanner(System.in); wage = stdin2.nextLine(); wage.replaceAll("\\s","").toLowerCase(); if (!(wage.equals("h") || wage.equals("s"))){ System.out.println("Input was not h or s; please try again"); } else if (wage.equals("h")){ System.out.print("Enter hourly wage: "); Scanner stdin4 = new Scanner(System.in); wages = stdin4.nextDouble(); Employee emp1 = new HourlyEmployee(empName, wages); emp.add(emp1); printMenu(); question();} else if (wage.equals("s")){ System.out.print("Enter annual salary: "); Scanner stdin5 = new Scanner(System.in); salary = stdin5.nextDouble(); Employee emp1 = new SalariedEmployee(empName, salary); printMenu(); question();}} else if (input.equals("c")){ for (int i = 0; i < emp.size(); i++){ System.out.println("Enter number of hours worked by " + emp.get(i) + ":"); } Scanner stdin = new Scanner(System.in); numHours = stdin.nextInt(); System.out.println("Pay: " + emp1.computePay(numHours)); System.out.print("Enter number of hours worked by " + empName); Scanner stdin2 = new Scanner(System.in); numHours = stdin2.nextInt(); System.out.println("Pay: " + emp1.computePay(numHours)); printMenu(); question();} else if (input.equals("r")){ System.out.print("Enter percentage increase: "); Scanner stdin = new Scanner(System.in); increase = stdin.nextDouble(); System.out.println("\nNew Wages"); System.out.println("---------"); // System.out.println(Employee.toString()); printMenu(); question(); } else if (input.equals("p")){ printArrayList(emp); printMenu(); question(); } else if (input.equals("q")){ exit(); } } } Here is one of the class files: public abstract class Employee { private String name; private double wage; protected Employee(String name, double wage){ this.name = name; this.wage = wage; } public String getName() { return name; } public double getWage() { return wage; } public void setName(String name) { this.name = name; } public void setWage(double wage) { this.wage = wage; } public void percent(double wage, double percent) { wage *= percent; } } And here are the errors: P.java:108: cannot find symbol symbol : variable emp1 location: class P System.out.println("Pay: " + emp1.computePay(numHours)); ^ P.java:112: cannot find symbol symbol : variable emp1 location: class P System.out.println("Pay: " + emp1.computePay(numHours)); ^ 2 errors I'm trying to the get paycheck to print out but i'm having trouble with how to call the method. It should take the user inputed numHours and calculate it then print on the paycheck for each employee. Thanks!

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  • When should I use String.Format or String.Concat instead of the concatenation operator?

    - by Kramii
    In C# it is possible to concatenate strings in several different ways: Using the concatenation operator: var newString = "The answer is '" + value + "'."; Using String.Format: var newString = String.Format("The answer is '{0}'.", value); Using String.Concat: var newString = String.Concat("The answer is '", value, "'."); What are the advantages / disadvantages of each of these methods? When should I prefer one over the others? The question arises because of a debate between developers. One never uses String.Format for concatenation - he argues that this is for formatting strings, not for concatenation, and that is is always unreadable because the items in the string are expressed in the wrong order. The other frequently uses String.Format for concatenation, because he thinks it makes the code easier to read, especially where there are several sets of quotes involved. Both these developers also use the concatenation operator and String.Builder, too.

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  • Does MS Test provide a default value equals comparison?

    - by fearofawhackplanet
    I want to test for example int orderId = myRepository.SubmitOrder(orderA); orderB = myRepository.GetOrder(orderId); Assert.AreEqual(orderA, orderB); // fail Obviously I need a value comparison here, but I don't want to have to provide an overridden Equals implementation for all of my classes purely for the sake of testing (it wouldn't be of any use in the rest of the app). Is there a provided generic method that just checks every field using reflection? Or if not, it is possible to write my own?

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  • Move constructor and assignment operator: why no default for derived classes?

    - by doublep
    Why there is default move constructor or assignment operator not created for derived classes? To demonstrate what I mean; having this setup code: #include <utility> struct A { A () { } A (A&&) { throw 0; } A& operator= (A&&) { throw 0; } }; struct B : A { }; either of the following lines throws: A x (std::move (A ()); A x; x = A (); but neither of the following does: B x (std::move (B ()); B x; x = B (); In case it matters, I tested with GCC 4.4.

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  • In Ruby, can the coerce() method know what operator it is that requires the help to coerce?

    - by Jian Lin
    In Ruby, it seems that a lot of coerce() help can be done by def coerce(something) [self, something] end that's is, when 3 + rational is needed, Fixnum 3 doesn't know how to handle adding a Rational, so it asks Rational#coerce for help by calling rational.coerce(3), and this coerce instance method will tell the caller: # I know how to handle rational + something, so I will return you the following: [self, something] # so that now you can invoke + on me, and I will deal with Fixnum to get an answer So what if most operators can use this method, but not when it is (a - b) != (b - a) situation? Can coerce() know which operator it is, and just handle those special cases, while just using the simple [self, something] to handle all the other cases where (a op b) == (b op a) ? (op is the operator).

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  • Why aren't operator conversions implicitly called for templated functions? (C++)

    - by John Gordon
    I have the following code: template <class T> struct pointer { operator pointer<const T>() const; }; void f(pointer<const float>); template <typename U> void tf(pointer<const float>); void g() { pointer<float> ptr; f(ptr); tf(ptr); } When I compile the code with gcc 4.3.3 I get a message (aaa.cc:17: error: no matching function for call to ‘tf(pointer<float>&)’) indicating that the compiler called 'operator pointer<const T>' for the non-templated function f(), but didn't for the templated function tf(). Why and is there any workaround short of overloading tf() with a const and non-const version? Thanks in advance for any help.

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  • Where would I use a bitwise operator in JavaScript?

    - by J-P
    I've read this (http://stackoverflow.com/quest...), so I know what bitwise operators are but I'm still not clear on how one might use them... Can anyone offer any real-world examples of where a bitwise operator would be useful in JavaScript? Thanks. Edit: Just digging into the jQuery source I've found a couple of places where bitwise operators are used, for example: (only the & operator) // Line 2756: event.which = (event.button & 1 ? 1 : ( event.button & 2 ? 3 : ( event.button & 4 ? 2 : 0 ) )); // Line 2101 var ret = a.compareDocumentPosition(b) & 4 ? -1 : a === b ? 0 : 1;

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  • Java: How to check if a date Object equals yesterday?

    - by tzippy
    Right now I am using this code Calendar cal = Calendar.getInstance(); SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd"); cal.set(cal.get(Calendar.YEAR), cal.get(Calendar.MONTH), cal.get(Calendar.DATE) - 1, 12, 0, 0); //Sets Calendar to "yeserday, 12am" if(sdf.format(getDateFromLine(line)).equals(sdf.format(cal.getTime()))) //getDateFromLine() returns a Date Object that is always at 12pm {...CODE There's got to be a smoother way to check if the date returned by getdateFromLine() is yesterday's date. Only the date matters, not the time. That's why I used SimpleDateFormat. Thanks for your help in advance!

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  • Is it possible to pass arithmetic operators to a method in java?

    - by drJames
    Right now I'm going to have to write a method that looks like this: public String Calculate(String Operator, Double Operand1, Double Operand2) { if (Operator.equals("+")) { return String.valueOf(Operand1 + Operand2); } else if (Operator.equals("-")) { return String.valueOf(Operand1 - Operand2); } else if (Operator.equals("*")) { return String.valueOf(Operand1 * Operand2); } else { return "error..."; } } It would be nice if I could write the code more like this: public String Calculate(String Operator, Double Operand1, Double Operand2) { return String.valueOf(Operand1 Operator Operand2); } So Operator would replace the Arithmetic Operators (+, -, *, /...) Does anyone know if something like this is possible in java?

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  • Is it possible to pass arithmatic operators to a method in java?

    - by user349611
    Right now I'm going to have to write a method that looks like this: public String Calculate(String Operator, Double Operand1, Double Operand2) { if (Operator.equals("+")) { return String.valueOf(Operand1 + Operand2); } else if (Operator.equals("-")) { return String.valueOf(Operand1 - Operand2); } else if (Operator.equals("*")) { return String.valueOf(Operand1 * Operand2); } else { return "error..."; } } It would be nice if I could write the code more like this: public String Calculate(String Operator, Double Operand1, Double Operand2) { return String.valueOf(Operand1 Operator Operand2); } So Operator would replace the Arithmetic Operators (+, -, *, /...) Does anyone know if something like this is possible in java?

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  • Why does String.Equals(Object obj) check to see if this == null?

    - by m-y
    // Determines whether two strings match. [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)] public override bool Equals(Object obj) { //this is necessary to guard against reverse-pinvokes and //other callers who do not use the callvirt instruction if (this == null) throw new NullReferenceException(); String str = obj as String; if (str == null) return false; if (Object.ReferenceEquals(this, obj)) return true; return EqualsHelper(this, str); } The part I don't understand is the fact that it is checking for the current instance, this, against null. The comment is a bit confusing, so I was wondering what does that comment actually mean? Can anyone give an example of how this could break if that check was not there, and does this mean that I should also place that check in my classes?

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