Java Programming Multiple Choice Questions - Garbage Collection

This section focuses on the "Garbage Collection" in Java programming. These Multiple Choice Questions (MCQ) should be practiced to improve the Java programming skills required for various interviews (campus interviews, walk-in interviews, company interviews), placements and other competitive examinations.

1. What allows the programmer to destroy an object x?

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

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2. Which statement is true?

A. Programs will not run out of memory.
B. Objects that are referred to by other objects will never be garbage collected.
C. Objects that will never again be used are eligible for garbage collection.
D. Objects that can be reached from a live thread will never be garbage collected.

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3. Which of the below is not a memory leak solution?

A. GC parameter tuning
B. Code changes
C. Process restart
D. JVM parameter tuning

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4. Which of the below is not a Java Profiler?

A. JVM
B. JProfiler
C. JConsole
D. Eclipse Profiler

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5. Which statement is true?

A. All objects that are eligible for garbage collection will be garbage collected by the garbage collector.
B. Objects from a class with the finalize() method overridden will never be garbage collected.
C. Objects with at least one reference will never be garbage collected.
D. Objects instantiated within anonymous inner classes are placed in the garbage collectible heap.

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6. How to get prints of shared object memory maps or heap memory maps for a given process?

A. jmap
B. jvmmap
C. memorymap
D. memorypath

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7. What is -Xms and -Xmx while starting jvm?

A. Initial; Maximum memory
B. Initial memory
C. Maximum memory
D. Maximum; Initial memory

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8. Which of the following has the highest memory requirement?

A. Stack
B. Class
C. JVM
D. Heap

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9. Where is a new object allocated memory?

A. Young space
B. JVM
C. Young or Old space depending on space availability
D. Old space

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10. Which of the following is a garbage collection technique?

A. Sweep model
B. Mark and sweep model
C. Space management model
D. Cleanup model

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11. When is the B object, created in line 3, eligible for garbage collection?

  
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 */
}

A. after line 5
B. after line 6
C. after line 7
D. There is no way to be absolutely certain.

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12. How many objects are eligible for garbage collection after execution of line ?

  
public class Test
{
	public static void main(String[] args)
	{
		m1(); // Line
	}
	static void m1()
	{
		Test t1 = new Test();
		Test t2 = new Test();
	}
}

A. 0
B. 1
C. 2
D. 3

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13. After line 11 runs, how many objects are eligible for garbage collection?

  
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();
	}
}

A. 0
B. 1
C. 2
D. 3

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14. When is the Demo object eligible for garbage collection?

  
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();
	}
}

A. After line 7
B. After line 8
C. After the start() method completes
D. When the instance running this code is made eligible for garbage collection.

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15. How many objects are eligible for garbage collection after execution of line 8?

  
public class Test
{
	public static void main(String [] args)
	{
		Test t1 = new Test();
		Test t2 = m1(t1); // line 6
		Test t3 = new Test();
		t2 = t3; // line 8
	}
	static Test m1(Test temp)
	{
		temp = new Test();
		return temp;
	}
}

A. 0
B. 1
C. 2
D. 3

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16. When is the Float object, created in line 3, eligible for garbage collection?

  
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 */
}

A. just after line 5
B. just after line 6
C. just after line 7
D. just after line 8

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