Java Puzzles: library puzzlers

public class PingPong {
    public static synchronized void main(String[] a) {
        Thread t = new Thread() {
            public void run() { pong(); }
        };
        t.run();
        System.out.print("Ping");
    }

    static synchronized void pong() {
        System.out.print("Pong");
    }
}

import java.util.*;

public class Worker extends Thread {
    private volatile boolean quittingTime = false;
    public void run() {
        while (!quittingTime)
            pretendToWork();
        System.out.println("Beer is good");
    }
    private void pretendToWork() {
        try {
            Thread.sleep(300); // Sleeping on the job?
        } catch (InterruptedException ex) { }
    }

    // It's quitting time, wait for worker - Called by good boss
    synchronized void quit() throws InterruptedException {
        quittingTime = true;
        join();
    }
    // Rescind quitting time - Called by evil boss
    synchronized void keepWorking() {
        quittingTime = false;
    }

    public static void main(String[] args)
            throws InterruptedException {
        final Worker worker = new Worker();
        worker.start();

        Timer t = new Timer(true); // Daemon thread
        t.schedule(new TimerTask() {
            public void run() { worker.keepWorking(); }
        }, 500);

        Thread.sleep(400);
        worker.quit();
    }
}

import java.util.*; import java.lang.reflect.*;

public class Reflector {
    public static void main(String[] args) throws Exception {
        Set s = new HashSet();
        s.add("foo");
        Iterator it = s.iterator();
        Method m = it.getClass().getMethod("hasNext");
        System.out.println(m.invoke(it));
    }
}

public class Pet {
    public final String name;
    public final String food;
    public final String sound;

    public Pet(String name, String food, String sound) {
        this.name = name;
        this.food = food;
        this.sound = sound;
    }

    public void eat() {
        System.out.println(name + ": Mmmmm, " + food);
    }
    public void play() {
        System.out.println(name + ": " + sound + " " + sound);
    }
    public void sleep() {
        System.out.println(name + ": Zzzzzzz...");
    }

    public void live() {
        new Thread() {
            public void run() {
                while (true) {
                    eat();
                    play();
                    sleep();
                }
            }
        }.start();
    }

    public static void main(String[] args) {
        new Pet("Fido", "beef", "Woof").live();
    }
}

public class Outer {
    public static void main(String[] args) throws Exception {
        new Outer().greetWorld();
    }

    private void greetWorld() throws Exception {
        System.out.println(Inner.class.newInstance());
    }

    public class Inner {
        public String toString() {
            return "Hello world";
        }
    }
}

public class Greeter {
    public static void main (String[] args) {
        String greeting = "Hello world";
        for (int i = 0; i < greeting.length(); i++)
            System.out.write(greeting.charAt(i));
    }
}

public class BeerBlast {
    static final String COMMAND = "java BeerBlast slave";

    public static void main(String[] args) throws Exception {
        if (args.length == 1 && args[0].equals("slave")) {
            for (int i = 99; i > 0; i--) {
                System.out.println(i + " bottles of beer on the wall");
                System.out.println(i + " bottles of beer");
                System.out.println("You take one down, pass it around,");
                System.out.println((i-1) + " bottles of beer on the wall");
                System.out.println();
            }
        } else {
            // Master
            Process process = Runtime.getRuntime().exec(COMMAND);
            int exitValue = process.waitFor();
            System.out.println("exit value = " + exitValue);
        }
    }
}

public class CopyDog {
    public static void main(String[] args) {
        Dog newDog = ??? ; // You figure out what to put here

        // This line should print false
        System.out.println(newDog == Dog.INSTANCE);

        // This line should print "Woof"
        System.out.println(newDog);
    }
}

public class Dog extends Exception {
    public static final Dog INSTANCE = new Dog();
    private Dog() { }

    public String toString() {
        return "Woof";
    }
}

public class SelfInterruption {
    public static void main(String[] args) {
        Thread.currentThread().interrupt();

        if (Thread.interrupted()) {
            System.out.println("Interrupted: " + Thread.interrupted());
        } else {
            System.out.println("Not interrupted: " + Thread.interrupted());
        }
    }
}

public class Lazy {
    private static boolean initialized = false;

    static {
        Thread t = new Thread(new Runnable() {
            public void run() {
                initialized = true;
            }
        });
        t.start();
        try {
            t.join();
        } catch(InterruptedException e) {
            throw new AssertionError(e);
        }
    }

    public static void main(String[] args) {
        System.out.println(initialized);
    }
}