Which of the following statements about the hashcode() method are incorrect?

1. The value returned by hashcode() is used in some collection classes to help locate objects.
2. The hashcode() method is required to return a positive int value.
3. The hashcode() method in the String class is the one inherited from Object.
4. Two new empty String objects will produce identical hashcodes.

1. The Iterator interface declares only three methods: hasNext, next and remove.
2. The ListIterator interface extends both the List and Iterator interfaces.
3. The ListIterator interface provides forward and backward iteration capabilities.
4. The ListIterator interface provides the ability to modify the List during iteration.
5. The ListIterator interface provides the ability to determine its position in the List.

1. hashCode() doesn't have to be overridden if equals() is.
2. equals() doesn't have to be overridden if hashCode() is.
3. hashCode() can always return the same value, regardless of the object that invoked it.
4. equals() can be true even if it's comparing different objects.

x = 0;
if (x1.hashCode() != x2.hashCode() )  x = x + 1;
if (x3.equals(x4) )  x = x + 10;
if (!x5.equals(x6) ) x = x + 100;
if (x7.hashCode() == x8.hashCode() )  x = x + 1000;
System.out.println("x = " + x);

class Test1 
{
    public int value;
    public int hashCode() { return 42; }
}
class Test2 
{
    public int value;
    public int hashcode() { return (int)(value^5); }
}

class Happy extends Thread 
{ 
    final StringBuffer sb1 = new StringBuffer(); 
    final StringBuffer sb2 = new StringBuffer(); 

    public static void main(String args[]) 
    { 
        final Happy h = new Happy(); 

        new Thread() 
        { 
            public void run() 
            { 
                synchronized(this) 
                { 
                    h.sb1.append("A"); 
                    h.sb2.append("B"); 
                    System.out.println(h.sb1); 
                    System.out.println(h.sb2); 
                } 
            } 
        }.start(); 

        new Thread() 
        { 
            public void run() 
            { 
                synchronized(this) 
                { 
                    h.sb1.append("D"); 
                    h.sb2.append("C"); 
                    System.out.println(h.sb2); 
                    System.out.println(h.sb1); 
                } 
            } 
        }.start(); 
    } 
}

class MyThread extends Thread 
{
    public static void main(String [] args) 
    {
        MyThread t = new MyThread(); /* Line 5 */
        t.run();  /* Line 6 */
    }

    public void run() 
    {
        for(int i=1; i < 3; ++i) 
        {
            System.out.print(i + "..");
        }
    }
}

public class Test107 implements Runnable 
{ 
    private int x; 
    private int y; 

    public static void main(String args[]) 
    {
        Test107 that = new Test107(); 
        (new Thread(that)).start(); 
        (new Thread(that)).start(); 
    } 
    public synchronized void run() 
    {
        for(int i = 0; i < 10; i++) 
        { 
            x++; 
            y++; 
            System.out.println("x = " + x + ", y = " + y); /* Line 17 */
        } 
    } 
} 

class MyThread extends Thread 
{ 
    MyThread() {} 
    MyThread(Runnable r) {super(r); } 
    public void run() 
    { 
        System.out.print("Inside Thread ");
    } 
} 
class MyRunnable implements Runnable 
{ 
    public void run() 
    { 
        System.out.print(" Inside Runnable"); 
    } 
} 
class Test 
{  
    public static void main(String[] args) 
    { 
        new MyThread().start(); 
        new MyThread(new MyRunnable()).start(); 
    } 
}