java roadtrip - Page 207

Rounding a double to 5 decimal places

- by Kevin Boyd

How do I round a double to 5 decimal places, without using DecimalFormat?

I have made this calculator program in Java. This works well only when two numbers are calculated at one time. That means to get the sum of 1+2+3 you have to go this way : press 1 press + press 2 press = press + press 3 press = and it calculates it as 6. But I want to program this so that I can get the answer by: press 1 press + press 2 press + press 3 press = but this gives the answer 5!!! How to code this so that it works like an ordinary calculator? Here is my code: import java.awt.*; import java.awt.event.*; import javax.swing.*; public class cal1 extends JFrame { double op1 = 0d, op2 = 0d; double result = 0d; char action; boolean b = false; boolean pressequal = false; public cal1() { makeUI(); } private void makeUI() { setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); setSize(400, 400); b0 = new JButton("0"); b1 = new JButton("1"); b2 = new JButton("2"); b3 = new JButton("3"); b4 = new JButton("4"); b5 = new JButton("5"); b6 = new JButton("6"); b7 = new JButton("7"); b8 = new JButton("8"); b9 = new JButton("9"); bDot = new JButton("."); bMul = new JButton("*"); bDiv = new JButton("/"); bPlus = new JButton("+"); bMinus = new JButton("-"); bEq = new JButton("="); t = new JTextField(12); t.setFont(new Font("Tahoma", Font.PLAIN, 24)); t.setHorizontalAlignment(JTextField.RIGHT); numpad = new JPanel(); display = new JPanel(); numpad.add(b7); numpad.add(b8); numpad.add(b9); numpad.add(bMul); numpad.add(b4); numpad.add(b5); numpad.add(b6); numpad.add(bDiv); numpad.add(b1); numpad.add(b2); numpad.add(b3); numpad.add(bMinus); numpad.add(bDot); numpad.add(b0); numpad.add(bEq); numpad.add(bPlus); numpad.setLayout(new GridLayout(4, 5, 5, 4)); display.add(t); add(display, BorderLayout.NORTH); add(numpad, BorderLayout.CENTER); t.addKeyListener(new KeyAdapter() { @Override public void keyTyped(KeyEvent e) { typeOnt(e); } }); b0.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { b0pressed(e); } }); b1.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { b1pressed(e); } }); b2.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { b2pressed(e); } }); b3.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { b3pressed(e); } }); b4.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { b4pressed(e); } }); b5.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { b5pressed(e); } }); b6.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { b6pressed(e); } }); b7.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { b7pressed(e); } }); b8.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { b8pressed(e); } }); b9.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { b9pressed(e); } }); bDot.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { bDotpressed(e); } }); bPlus.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { bPlusPressed(e); } }); bMinus.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { bMinusPressed(e); } }); bMul.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { bMulPressed(e); } }); bDiv.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { bDivPressed(e); } }); bEq.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { bEqpressed(e); } }); } void typeOnt(KeyEvent e) { e.consume(); } void b0pressed(ActionEvent e) { if (b) { t.setText(null); b = false; t.setText(t.getText() + "0"); } else { t.setText(t.getText() + "0"); } } void b1pressed(ActionEvent e) { if (b) { t.setText(null); b = false; t.setText(t.getText() + "1"); } else { t.setText(t.getText() + "1"); } } void b2pressed(ActionEvent e) { if (b) { t.setText(null); b = false; t.setText(t.getText() + "2"); } else { t.setText(t.getText() + "2"); } } void b3pressed(ActionEvent e) { if (b) { t.setText(null); b = false; t.setText(t.getText() + "3"); } else { t.setText(t.getText() + "3"); } } void b4pressed(ActionEvent e) { if (b) { t.setText(null); b = false; t.setText(t.getText() + "4"); } else { t.setText(t.getText() + "4"); } } void b5pressed(ActionEvent e) { if (b) { t.setText(null); b = false; t.setText(t.getText() + "5"); } else { t.setText(t.getText() + "5"); } } void b6pressed(ActionEvent e) { if (b) { t.setText(null); b = false; t.setText(t.getText() + "6"); } else { t.setText(t.getText() + "6"); } } void b7pressed(ActionEvent e) { if (b) { t.setText(null); b = false; t.setText(t.getText() + "7"); } else { t.setText(t.getText() + "7"); } } void b8pressed(ActionEvent e) { if (b) { t.setText(null); b = false; t.setText(t.getText() + "8"); } else { t.setText(t.getText() + "8"); } } void b9pressed(ActionEvent e) { if (b) { t.setText(null); b = false; t.setText(t.getText() + "9"); } else { t.setText(t.getText() + "9"); } } void bDotpressed(ActionEvent e) { if (!t.getText().contains(".")) { if (b) { t.setText(null); b = false; t.setText(t.getText() + "0."); } else if (t.getText().isEmpty()) { t.setText("0."); } else { t.setText(t.getText() + "."); } } } void bPlusPressed(ActionEvent e) { b = true; action = '+'; op1 = Double.parseDouble(t.getText()); } void bMinusPressed(ActionEvent e) { b = true; action = '-'; op1 = Double.parseDouble(t.getText()); } void bMulPressed(ActionEvent e) { b = true; action = '*'; op1 = Double.parseDouble(t.getText()); } void bDivPressed(ActionEvent e) { b = true; action = '/'; op1 = Double.parseDouble(t.getText()); } void bEqpressed(ActionEvent e) { op2 = Double.parseDouble(t.getText()); doCal(); } void doCal() { switch (action) { case '+': result = op1 + op2; break; case '-': result = op1 - op2; break; case '*': result = op1 * op2; break; case '/': result = op1 / op2; break; } t.setText(String.valueOf(result)); } public static void main(String[] args) { new cal1().setVisible(true); } JButton b0; JButton b1; JButton b2; JButton b3; JButton b4; JButton b5; JButton b6; JButton b7; JButton b8; JButton b9; JButton bDot; JButton bPlus; JButton bMinus; JButton bMul; JButton bDiv; JButton bEq; JPanel display; JPanel numpad; JTextField t; }

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