You have to assign repeat in your while-loop so it becomes false if the user says yes:

repeat = !input.equalsIgnoreCase("yes"); 

If you have a for-loop want to quit you need only a "break;" , so best you have a variable is always watched by whether they are "0", and if so then any for loop executes a break; out. To Example:

import java.util.Scanner;

public class Stopky {

    private volatile static int check = 1;

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Stlačte 0 pre začatie stopiek."); // "Press 0 for start
        int start = sc.nextInt();
        if (start == 0) {
            new Thread(new Runnable() {
                @Override
                public void run() {
                    while (check != 0 && sc.hasNextInt())
                        check = sc.nextInt();
                }
            }).start();
            for (int hodiny = 0; hodiny < 24; hodiny++) //hours
            {
                for (int minuty = 0; minuty < 60; minuty++) //minutes
                {
                    for (int sekundy = 0; sekundy < 60; sekundy++) //seconds
                    {
                        for (int ms = 0; ms < 1000; ms++) //miliseconds
                            try {
                                Thread.sleep(1);
                            } catch (Exception e) {
                            }
                        {
                            if (check == 0)
                                break;
                            System.out.println(hodiny + ":" + minuty + ":" + sekundy);
                        }
                        if (check == 0)
                            break;
                    }
                    if (check == 0)
                        break;
                }
                if (check == 0)
                    break;
            }
        }
        sc.close();
    }
}

Use break:

while (true) {
    ....
    if (obj == null) {
        break;
    }
    ....
}

However, if your code looks exactly like you have specified you can use a normal while loop and change the condition to obj != null:

while (obj != null) {
    ....
}

For more readable code you can use a boolean variable and assign it to true according to your input equals to "y" condition

public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        boolean stopFlag= false;
        do{
            System.out.println("She sells seashells by the seashore.");
            System.out.println("Do you want to hear it again?");
            String userInput =input.next();
            if(!userInput.equals("y"))
                stopFlag=true;
        }while (!stopFlag);
    }

In any kind of loop

• break can be used to exit the loop
• continue causes the loop to continue with the next iteration
• return breaks the loop and causes the container method to exit by giving the control back to the caller

In your case you can test if the condition is met like this:

input = User_Input.next();
if ("exit".equals(input))
    break;

break; is what you need to break out of any looping statement like for, while or do-while.

In your case, its going to be like this:-

for(int x = 10; x < 20; x++) {
         // The below condition can be present before or after your sysouts, depending on your needs.
         if(x == 15){
             break; // A unlabeled break is enough. You don't need a labeled break here.
         }
         System.out.print("value of x : " + x );
         System.out.print("\n");
}

You should try to use "a real termination condition" in order to terminate a while loop (or any loop for that matter); it's cleaner and should be easier to understand by everyone else.

In your case, I think it's better to have a do-while loop with some condition around this logic: num % 2 == 0, and an inner while loop for handling user input/validation.

If you still want to break loops abruptly, have a look here.

If you still need some help with the code, hit me up and I'll sketch up something.

The loop should not write to an in-memory buffer, but to the file writer directly (wrapped inside a BufferedWriter). This will avoid running out of memory.

You should start a new thread which executes your while loop, and tests at each iteration if the thread has been asked to interrupt itself, using Thread.currentThread().isInterrupted(). Once interrupted, the thread should stop the while loop, and close the writer.

Have your main thread read from the command line, and when the stop command is entered, call interrupt() on the writer thread.

Your condition is always true. If you want to react to a user typing in "quit" while entering a new guess, you can do it with an infinite loop and a break, like this:

while (true) {
    System.out.println("Please every a word or QUIT to exit");
    String guess = input.nextLine();
    if (quit.equalsIgnoreCase(guess)) {
        break;
    }
    for(int i = 0; i < words.length; i++) {
        ...
    }
}