Java Programming

Java Programming

Garbage Collections has 9 Questions

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 */
} 
When is the B object, created in line 3, eligible for garbage collection?

after line 5
after line 6
after line 7
There is no way to be absolutely certain.
Which statement is true?

Programs will not run out of memory.
Objects that will never again be used are eligible for garbage collection.
Objects that are referred to by other objects will never be garbage collected.
Objects that can be reached from a live thread will never be garbage collected.
class HappyGarbage01 
{ 
    public static void main(String args[]) 
    {
        HappyGarbage01 h = new HappyGarbage01(); 
        h.methodA(); /* Line 6 */
    } 
    Object methodA() 
    {
        Object obj1 = new Object(); 
        Object [] obj2 = new Object[1]; 
        obj2[0] = obj1; 
        obj1 = null; 
        return obj2[0]; 
    } 
}
Where will be the most chance of the garbage collector being invoked?

After line 9
After line 10
After line 11
Garbage collector never invoked in methodA()
class Bar { } 
class Test 
{  
    Bar doBar() 
    {
        Bar b = new Bar(); /* Line 6 */
        return b; /* Line 7 */
    } 
    public static void main (String args[]) 
    { 
        Test t = new Test();  /* Line 11 */
        Bar newBar = t.doBar();  /* Line 12 */
        System.out.println("newBar"); 
        newBar = new Bar(); /* Line 14 */
        System.out.println("finishing"); /* Line 15 */
    } 
}
At what point is the Bar object, created on line 6, eligible for garbage collection?

after line 12
after line 14
after line 7, when doBar() completes
after line 15, when main() completes
class Test 
{  
    private Demo d; 
    void start() 
    {  
        d = new Demo(); 
        this.takeDemo(d); /* Line 7 */
    } /* Line 8 */
    void takeDemo(Demo demo) 
    { 
        demo = null;  
        demo = new Demo(); 
    } 
}
When is the Demo object, created on line 4, eligible for garbage collection?

After line 7
After line 8
After the start() method completes
When the instance running this code is made eligible for garbage collection.
public class X 
{
    public static void main(String [] args) 
    {
        X x = new X();
        X x2 = m1(x); /* Line 6 */
        X x4 = new X();
        x2 = x4; /* Line 8 */
        doComplexStuff();
    }
    static X m1(X mx) 
    {
        mx = new X();
        return mx;
    }
}
After line 8 runs. how many objects are eligible for garbage collection?

0
1
2
3
public Object m() 
{  
    Object o = new Float(3.14F); 
    Object [] oa = new Object[l];
    oa[0] = o; /* Line 5 */
    o = null;  /* Line 6 */
    oa[0] = null; /* Line 7 */
    return o; /* Line 8 */
}
When is the Float object, created in line 3, eligible for garbage collection?

just after line 5
just after line 6
just after line 7
just after line 8
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();
    }
}
after line 11 runs, how many objects are eligible for garbage collection?

0
1
2
3
What allows the programmer to destroy an object x?

x.delete()
x.finalize()
Runtime.getRuntime().gc()
Only the garbage collection system can destroy an object.