Online Java Programming Test - Java Programming Test 9

What will be the output of the program?

class Super
{ 
    public int i = 0; 

    public Super(String text) /* Line 4 */
    {
        i = 1; 
    } 
} 

class Sub extends Super
{
    public Sub(String text)
    {
        i = 2; 
    } 

    public static void main(String args[])
    {
        Sub sub = new Sub("Hello"); 
        System.out.println(sub.i); 
    } 
}

What will be the output of the program?

class Base
{ 
    Base()
    {
        System.out.print("Base");
    }
} 
public class Alpha extends Base
{ 
    public static void main(String[] args)
    { 
        new Alpha(); /* Line 12 */
        new Base(); /* Line 13 */
    } 
}

What will be the output of the program?

import java.util.*;
public class NewTreeSet2 extends NewTreeSet 
{
    public static void main(String [] args) 
    {
        NewTreeSet2 t = new NewTreeSet2();
        t.count();
    }
}
protected class NewTreeSet
{
    void count() 
    {
        for (int x = 0; x < 7; x++,x++ ) 
        {
            System.out.print(" " + x);
        }
    }
}

Which two statements are true for any concrete class implementing the java.lang.Runnable interface?

1. You can extend the Runnable interface as long as you override the public run() method.
2. The class must contain a method called run() from which all code for that thread will be initiated.
3. The class must contain an empty public void method named run().
4. The class must contain a public void method named runnable().
5. The class definition must include the words implements Threads and contain a method called run().
6. The mandatory method must be public, with a return type of void, must be called run(), and cannot take any arguments.

What will be the output of the program?

public class X 
{  
    public static void main(String [] args) 
    {
        try 
        {
            badMethod();  
            System.out.print("A"); 
        }  
        catch (Exception ex) 
        {
            System.out.print("B");  
        } 
        finally 
        {
            System.out.print("C"); 
        } 
        System.out.print("D"); 
    }  
    public static void badMethod() 
    {
        throw new Error(); /* Line 22 */
    } 
}

What will be the output of the program?

public class X 
{  
    public static void main(String [] args) 
    {
        try 
        {
            badMethod(); /* Line 7 */
            System.out.print("A"); 
        } 
        catch (Exception ex) /* Line 10 */
        {
            System.out.print("B"); /* Line 12 */
        } 
        finally /* Line 14 */
        {
            System.out.print("C"); /* Line 16 */
        }  
        System.out.print("D"); /* Line 18 */
    } 
    public static void badMethod() 
    {
        throw new RuntimeException(); 
    } 
}

Which interface does java.util.Hashtable implement?

What will be the output of the program?

package foo; 
import java.util.Vector; /* Line 2 */
private class MyVector extends Vector 
{
    int i = 1; /* Line 5 */
    public MyVector() 
    { 
        i = 2; 
    } 
} 
public class MyNewVector extends MyVector 
{
    public MyNewVector () 
    { 
        i = 4; /* Line 15 */
    } 
    public static void main (String args []) 
    { 
        MyVector v = new MyNewVector(); /* Line 19 */
    } 
}

What two statements are true about properly overridden hashCode() and equals() methods?

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.

Which three are methods of the Object class?

1. notify();
2. notifyAll();
3. isInterrupted();
4. synchronized();
5. interrupt();
6. wait(long msecs);
7. sleep(long msecs);
8. yield();

Which cannot directly cause a thread to stop executing?

Which method registers a thread in a thread scheduler?

public class MyRunnable implements Runnable 
{
    public void run() 
    {
        // some code here
    }
}

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 */
} 

class X2 
{
    public X2 x;
    public static void main(String [] args) 
    {
        X2 x2 = new X2();  /* Line 6 */
        X2 x3 = new X2();  /* Line 7 */
        x2.x = x3;
        x3.x = x2;
        x2 = new X2();
        x3 = x2; /* Line 11 */
        doComplexStuff();
    }
}

Which of the following would compile without error?

What will be the output of the program?

String x = new String("xyz");
String y = "abc";
x = x + y;

What will be the output of the program?

System.out.println(Math.sqrt(-4D));

What will be the output of the program?

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(); 
    } 
}

Which statement is true given the following?

Double d = Math.random();