Java Puzzles: classy puzzlers

public class Confusing {
    private Confusing(Object o) {
        System.out.println("Object");
    }

    private Confusing(double[] dArray) {
        System.out.println("double array");
    }

    public static void main(String[] args) {
        new Confusing(null);
    }
}

class Counter {
    private static int count = 0;
    public static final synchronized void increment() {
        count++;
    }
    public static final synchronized int getCount() {
        return count; 
    } 
}

class Dog extends Counter {
    public Dog() { }
    public void woof() { increment(); }
} 

class Cat extends Counter {
    public Cat() { } 
    public void meow() { increment(); }
}

public class Ruckus {
    public static void main(String[] args) { 
        Dog dogs[] = { new Dog(), new Dog() };
        for (int i = 0; i < dogs.length; i++)
            dogs[i].woof();
        Cat cats[] = { new Cat(), new Cat(), new Cat() };
        for (int i = 0; i < cats.length; i++)
            cats[i].meow();
        System.out.print(Dog.getCount() + " woofs and ");
        System.out.println(Cat.getCount() + " meows");
    }
}

class Dog {
    public static void bark() {
        System.out.print("woof ");
    }
}

class Basenji extends Dog {
    public static void bark() { }
}

public class Bark {
    public static void main(String args[]) {
        Dog woofer = new Dog();
        Dog nipper = new Basenji();
        woofer.bark();
        nipper.bark();
    }
}

import java.util.Calendar;

public class Elvis {
    public static final Elvis INSTANCE = new Elvis();
    private final int beltSize;
    private static final int CURRENT_YEAR =
        Calendar.getInstance().get(Calendar.YEAR);

    private Elvis() {
        beltSize = CURRENT_YEAR - 1930;
    }

    public int beltSize() {
        return beltSize;
    }

    public static void main(String[] args) {
        System.out.println("Elvis wears a size " +
                           INSTANCE.beltSize() + " belt.");
    } 
}

public class Type1 {
    public static void main(String[] args) {
        String s = null;
        System.out.println(s instanceof String);
    }
}

public class Type2 {
    public static void main(String[] args) {
        System.out.println(new Type2() instanceof String);
    }
}

public class Type3 {
    public static void main(String args[]) {
        Type3 t2 = (Type3) new Object();
    }
}

class Point {
    protected final int x, y;
    private final String name; // Cached at construction time
    Point(int x, int y) {
        this.x = x;
        this.y = y;
        name = makeName();
    }

    protected String makeName() {
        return "[" + x + "," + y + "]";
    }

    public final String toString() {
        return name;
    }
}

public class ColorPoint extends Point {
    private final String color;
    ColorPoint(int x, int y, String color) {
        super(x, y);
        this.color = color;
    }

    protected String makeName() {
       return super.makeName() + ":" + color;
    }

    public static void main(String[] args) {
        System.out.println(new ColorPoint(4, 2, "purple"));
    }
}

class Cache {
    static {
        initializeIfNecessary();
    }

    private static int sum;
    public static int getSum() {
        initializeIfNecessary();
        return sum;
    }

    private static boolean initialized = false;
    private static synchronized void initializeIfNecessary() {
        if (!initialized) {
            for (int i = 0; i < 100; i++)
                sum += i;
            initialized = true;
        }
    }
}

public class Client {
    public static void main(String[] args) {
        System.out.println(Cache.getSum()); 
    } 
}

// This is meant to represent a library class. You must not modify it.
public class Thing {
    public Thing(int i) {
    }
}

public class MyThing extends Thing {
    private final int arg;

    /*
     * This constructor is illegal. Rewrite it so that it has the same
     * effect but is legal.
     */
    public MyThing() {
        super(arg = (int)System.currentTimeMillis());
    }
}

public class Null {
    public static void greet() {
        System.out.println("Hello world!");
    }

    public static void main(String[] args) {
        ((Null) null).greet();
    } 
}

public class Creator {
    public static void main(String[] args) {
        for (int i = 0; i < 100; i++)
            Creature creature = new Creature();
        System.out.println(Creature.numCreated());
    }
}

class Creature {
    private static long numCreated = 0;

    public Creature() {
        numCreated++;
    }

    public static long numCreated() {
        return numCreated;
    }
}