Questions and answers for exam Preparation

MCQs

Total Questions : 97 | Page 6 of 10 pages

Question 51.
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

Discuss Question

Answer: Option C. -> just after line 7

Option A is wrong. This simply copies the object reference into the array.

Option B is wrong. The reference o is set to null, but, oa[0] still maintains the reference to

the Float object.

Option C is correct. The thread of execution will then not have access to the object.

Question 52.

What is the output of this program?

import java.util.*;
class Maps {
public static void main(String args[]) {
TreeMap obj = new TreeMap();
obj.put("A", new Integer(1));
obj.put("B", new Integer(2));
obj.put("C", new Integer(3));
System.out.println(obj.entrySet());
}
}

[A, B, C]
[1, 2, 3]
{A=1, B=2, C=3}
[A=1, B=2, C=3]

Discuss Question

Answer: Option D. -> [A=1, B=2, C=3]

obj.entrySet() method is used to obtain a set that contains the entries in the map.

This method provides set view of the invoking map.
Output:
$ javac Maps.java
$ java Maps
[A=1, B=2, C=3]

Question 53.

What is the output of this program?

class box {
int width;
int height;
int length;
int volume;
box() {
width = 5;
height = 5;
length = 6;
}
void volume() {
volume = width*height*length;
}
}
class constructor_output {
public static void main(String args[])
{
box obj = new box();
obj.volume();
System.out.println(obj.volume);
}
}

Discuss Question

Answer: Option B. -> 150

None.
output:
$ constructor_output.java
$ constructor_output
150

Question 54.

What is the output of this program?

class main_class {
public static void main(String args[])
{
int x = 9;
if (x == 9) {
int x = 8;
System.out.println(x);
}
}
}

9
8
Compilation error
Runtime error

Discuss Question

Answer: Option C. -> Compilation error

Two variables with the same name can't be created in a class.
output:
$ javac main_class.java
Exception in thread "main" java.lang.Error: Unresolved compilation problem:
Duplicate local variable x

Question 55.

Which of these class relies upon its subclasses for complete implementation of its methods?

Object class
abstract class
ArrayList class
None of the mentioned

Discuss Question

Answer: Option B. -> abstract class

None.

Question 56.

Which interface provides the capability to store objects using a key-value pair?

Java.util.Map
Java.util.Set
Java.util.List
Java.util.Collection

Discuss Question

Answer: Option A. -> Java.util.Map

An object that maps keys to values. A map cannot contain duplicate keys; each key can

map to at most one value.

Question 57.

Which of these statement is incorrect?

Every class must contain a main() method.
Applets do not require a main() method at all.
There can be only one main() method in a program.
main() method must be made public.

Discuss Question

Answer: Option A. -> Every class must contain a main() method.

Every class does not need to have a main() method, there can be only one main() method

which is made public.

Question 58.
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?

Discuss Question

Answer: Option B. -> 1

By the time line 8 has run, the only object without a reference is the one generated as a result of line 6. Remember that "Java is pass by value," so the reference variable x is not affected by the m1() method.

Ref: http://www.javaworld.com/javaworld/javaqa/2000-05/03-qa-0526-pass.html

Question 59.

What is Collection in Java?