1. What will be the output of this code?
class Test {
int x = 10;
public static void main(String[] args) {
Test t1 = new Test();
Test t2 = new Test();
t1.x = 20;
System.out.println(t2.x);
}
}
a) 10
b) 20
c) 0
d) Compilation error
2. Which concept is shown here?
class Animal {
void sound() { System.out.println("Animal sound"); }
}
class Dog extends Animal {
void sound() { System.out.println("Bark"); }
}
a) Overloading
b) Overriding
c) Encapsulation
d) Abstraction
3. Which constructor will be called?
class Demo {
Demo() { System.out.println("Default"); }
Demo(int x) { System.out.println("Parameterized"); }
public static void main(String[] args) {
Demo d = new Demo(5);
}
}
a) Default
b) Parameterized
c) Compilation error
d) Both
4. What will be printed?
class Parent {
void display() { System.out.println("Parent"); }
}
class Child extends Parent {
void display() { System.out.println("Child"); }
}
public class Test {
public static void main(String[] args) {
Parent p = new Child();
p.display();
}
}
a) Parent
b) Child
c) Compilation error
d) Runtime error
5. Which keyword is used to prevent method overriding?
a) abstract
b) static
c) final
d) private
6. What is the output?
String s1 = "Java";
String s2 = new String("Java");
System.out.println(s1 == s2);
a) true
b) false
c) Compilation error
d) Runtime error
7. Which statement about StringBuffer is TRUE?
a) Immutable like String
b) Mutable
c) Cannot store characters
d) Faster than StringBuilder
8. What will happen here?
try {
int a = 5 / 0;
} catch (Exception e) {
System.out.println("Exception");
}
a) ArithmeticException
b) Exception
c) Runtime error
d) No output
9. Which exception is a checked exception?
a) NullPointerException
b) SQLException
c) ArithmeticException
d) ArrayIndexOutOfBoundsException
10. What is the output?
try {
int arr[] = new int[2];
arr[2] = 10;
} catch (ArrayIndexOutOfBoundsException e) {
System.out.println("Caught");
}
a) Compilation error
b) Caught
c) Runtime error
d) No output
11. Which method belongs to String class?
a) reverse()
b) substring()
c) append()
d) capacity()
12. What is the default value of a class reference in Java?
a) ""
b) null
c) 0
d) undefined
13. Which method moves the cursor to the next token in StringTokenizer?
a) next()
b) nextToken()
c) hasNext()
d) split()
14. Which collection allows duplicate elements?
a) HashSet
b) ArrayList
c) TreeSet
d) LinkedHashSet
15. Which collection maintains insertion order?
a) HashSet
b) TreeSet
c) LinkedHashSet
d) PriorityQueue
16. Output of this code?
ArrayList<String> list = new ArrayList<>();
list.add("A");
list.add("B");
list.add("A");
System.out.println(list.size());
a) 2
b) 3
c) 1
d) Error
17. Which collection does not allow null values?
a) ArrayList
b) HashSet
c) TreeSet
d) LinkedList
18. What is the output?
Stack<Integer> stack = new Stack<>();
stack.push(10);
stack.push(20);
stack.pop();
System.out.println(stack.peek());
a) 10
b) 20
c) 0
d) Error
19. Which interface does Queue extend?
a) List
b) Collection
c) Set
d) Iterator
20. Which method removes all elements from a collection?
a) clear()
b) remove()
c) delete()
d) erase()
21. Which interface is implemented by ArrayList?
a) Map
b) List
c) Queue
d) Set
22. What will happen here?
HashSet<String> set = new HashSet<>();
set.add("One");
set.add("One");
System.out.println(set.size());
a) 2
b) 1
c) Error
d) Undefined
23. Which collection guarantees natural ordering of elements?
a) HashSet
b) TreeSet
c) LinkedHashSet
d) ArrayList
24. Which method is used to add an element at the beginning of a LinkedList?
a) add()
b) addFirst()
c) insert()
d) push()
25. Output of this code?
Queue<Integer> q = new LinkedList<>();
q.add(1);
q.add(2);
q.remove();
System.out.println(q.peek());
a) 1
b) 2
c) null
d) Error
