Java, while loop

Question

I am playing with Java and want to do a simple while loop that keeps going until the users does a <ctrl> z.

I have something like this

public static void main(String[] args) {

    //declare vars
    boolean isEvenResult;
    int num;

    //create objects
    Scanner input = new Scanner(System.in);
    EvenTester app = new EvenTester();

    //input user number
    System.out.print("Please enter a number: ");
    num = input.nextInt();

    while() {

        //call methods
        isEvenResult = app.isEven(num);

        if(isEvenResult) {
            System.out.printf("%d is even", num);
        } else {
            System.out.printf("%d is odd", num);
        }

    }//end while loop

}//end main

I tried while( input.hasNext() ) { ... but the code inside the while loop wouldn't execute.

thanks for the help

Answer 1

while (num != 'z')

Although if you are expecting a 'z' why are doing input.getInt()?

You may want to check out the Console class too.

Answer 2

//input user number
System.out.print("Please enter a number: ");

do {
    try {
     num = input.nextInt();
    } catch (Exception e) {
     break;
    }
    // call methods
    isEvenResult = app.isEven(num);

    if (isEvenResult) {
     System.out.printf("%d is even", num);
    } else {
     System.out.printf("%d is odd", num);
    }
} while (true);

When the user writes something non-numeric, the loop breaks.

Answer 3

If you want to loop until the user has to force break via Ctrl+Z, then just do while(true). But you want your nextInt() to be inside the loop, and maybe also your prompting statement.

Answer 4

You need to implement KeyBindings. Then you can make the determination to exit based off of what keys were pressed.

Answer 5

you are doing the input outside the loop,and it will run for only once.

System.out.print("Please enter a number: ");
num = input.nextInt();

Put your above code inside the loop.

Since you are having a system out inside the loop you will also come to know whether the control went inside the loop, obviously it should.

Also, try

while(true)

I wonder if while() alone is working.

Answer 6

TrueSoft's solution is dead on. The reasons it may not be working for the asker is are kinda outside the scope of the program.

The program works for me: I'm running it under Linux and enter Ctrl-D as the first thing on a line. Ctrl-D is end-of-file for Linux the same way that Ctrl-Z is for Windows. Program stops dead in its tracks, perfectly.

The Windows console (the black DOS box, whatever you want to call it) has a wrinkle: It reads input line-by-line. It won't see the Ctrl-Z until it's read the line, so it needs an Enter keyin before it will see the Ctrl-Z.

I'm unwilling to fire up Windows just to try this, but my guess is that CTRL-Z followed by the Enter key (just like after the number entries) should cause the program to stop cleanly.

There are system-y ways to make a Java program work on a character-by-character basis so you can handle any characters directly and respond immediately to Ctrl-Z. But that's advanced stuff and doesn't belong in a simple programming exercise like this. I think Ctrl-Z / Enter is an acceptable way to have the program end.