I'm new to programming, and I'm using java. Here's a program I wrote:

class HelloApp {

    static String hi;

    public static void main(String[] args) {
        int length = args.length;
        if (length > 0) {
            hi = args[0];
            sayHi();
        }
    }

    static void sayHi() {
        if (hi == "hello") {
            System.out.println("Hello!");
        }
    }
}

My question is: Why doesn't inputting "java HelloApp hello" make "Hello!" appear on the next line?