Inheritance - 1

What is the output of this program? class A { public int i; public int j; A() { i = 1; j = 2; } } class B extends A { int a; B() { super(); } } class super_use { public static void main(String args[]) { B obj = new B(); System.out.println(obj.i + " " + obj.j) } } a) 1 2 b) 2 1 c) Runtime Error d) Compilation Error

a) 1 2 Explanation: Keyword super is used to call constructor of class A by constructor of class B. Constructor of a initializes i & j to 1 & 2 respectively. output: $ javac super_use.java $ java super_use 1 2

Which two classes use the Shape class correctly? A. public class Circle implements Shape { private int radius; } B. public abstract class Circle extends Shape { private int radius; } C. public class Circle extends Shape { private int radius; public void draw(); } D. public abstract class Circle implements Shape { private int radius; public void draw(); } E. public class Circle extends Shape { private int radius; public void draw() { /* code here */ } } F. public abstract class Circle implements Shape { private int radius; public void draw() { /* code here */ } } a) B,E b) A,C c) C,E d) T,H

a) B,E Explanation: If one is extending any class, then they should use extends keyword not implements.

A class member declared protected becomes a member of subclass of which type? a) public member b) private member c) protected member d) static member

b) private member Explanation: A class member declared protected becomes a private member of subclass.

What is the output of this program? class A { int i; void display() { System.out.println(i); } } class B extends A { int j; void display() { System.out.println(j); } } class inheritance_demo { public static void main(String args[]) { B obj = new B(); obj.i=1; obj.j=2; obj.display(); } } a) 0 b) 1 c) 2 d) Compilation Error

c) 2 Explanation: Class A & class B both contain display() method, class B inherits class A, when display() method is called by object of class B, display() method of class B is executed rather than that of Class A. output: $ javac inheritance_demo.java $ java inheritance_demo 2

What is the output of this program? class A { int i; } class B extends A { int j; void display() { super.i = j + 1; System.out.println(j + " " + i); } } class inheritance { public static void main(String args[]) { B obj = new B(); obj.i=1; obj.j=2; obj.display(); } } a) 2 2 b) 3 3 c) 2 3 d) 3 2

c) 2 3 Explanation: None output: $ javac inheritance.java $ java inheritance 2 3

Which of these is correct way of inheriting class A by class B? a) class B + class A {} b) class B inherits class A {} c) class B extends A {} d) class B extends class A {}

c) class B extends A {}

Which of this keyword must be used to inherit a class? a) super b) this c) extent d) extends

d) extends