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.

void start() {  
    A a = new A(); 
    B b = new B(); 
    a.s(b);  
    b = null; /* Line 5 */
    a = null;  /* Line 6 */
    System.out.println("start completed"); /* Line 7 */
} 

public class Test 
{ 
    public static void main(String[] args) 
    {
        final StringBuffer a = new StringBuffer(); 
        final StringBuffer b = new StringBuffer(); 

        new Thread() 
        { 
            public void run() 
            {
                System.out.print(a.append("A")); 
                synchronized(b) 
                { 
                    System.out.print(b.append("B")); 
                } 
            } 
        }.start(); 
            
        new Thread() 
        {
            public void run() 
            {
                System.out.print(b.append("C")); 
                synchronized(a) 
                {
                    System.out.print(a.append("D")); 
                } 
            } 
        }.start(); 
    } 
}

import java.io.*;
public class MyProgram 
{
    public static void main(String args[])
    {
        FileOutputStream out = null;
        try 
        {
            out = new FileOutputStream("test.txt");
            out.write(122);
        }
        catch(IOException io) 
        {
            System.out.println("IO Error.");
        }
        finally 
        {
            out.close();
        }
    }
}

public class Test 
{
    public static void main(String [] args) 
    {
        int I = 1;
        do while ( I < 1 )
        System.out.print("I is " + I);
        while ( I > 1 ) ;
    }
}

class MyThread extends Thread 
{
    public static void main(String [] args) 
    {
        MyThread t = new MyThread();
        Thread x = new Thread(t);
        x.start(); /* Line 7 */
    }
    public void run() 
    {
        for(int i = 0; i < 3; ++i) 
        {
            System.out.print(i + "..");
        }
    }
}

1. protected abstract void m1();
2. static final void m1(){}
3. synchronized public final void m1() {}
4. private native void m1();

1. f1 == f2
2. f1 == f3
3. f2 == f1[1]
4. x == f1[0]
5. f == f1[0]

import java.awt.Button;
class CompareReference 
{
    public static void main(String [] args) 
    {
        float f = 42.0f;
        float [] f1 = new float[2];
        float [] f2 = new float[2];
        float [] f3 = f1;
        long x = 42;
        f1[0] = 42.0f;
    }
}