Java, Inheritance, Frequently asked questions in technical aptitude. SCJP Dumbs.

1. Inheritance
Duration : 30 mins.

2. Q1 .Consider the following code:
class Base
{
private float f = 1.0f;
protected void setF(float f1){ this.f = f1; }
}
class Base2 extends Base
{
private float f = 2.0f;
//1
}
Which of the following options is a valid example of overriding?
Select 2 correct options
a protected void setF(float f1){ this.f = 2*f1; }
b public void setF(double f1){ this.f = (float) 2*f1; }
c public void setF(float f1){ this.f = 2*f1; }
d private void setF(float f1){ this.f = 2*f1; }
e float setF(float f1){ this.f = 2*f1; return f;}
Ans: a,c

3. Q2
You are modeling a class hierarchy for living things.
You have a class LivingThing which has an abstract method reproduce().
Now, you want to have 2 subclasses of LivingThing, Plant and Animal.
Obviously, both do reproduce but the mechanisms are different.
What would you do?
Select 1 correct option.
a Overload the reproduce method in Plant and Animal Clases
b Overload the reproduce method in LivingThing Class.
c Override the reproduce method in Plant and Animal Clases
d Either overload or override, it depends on the taste of the designer.
Ans: c

4. Q3
An abstract method cannot be overridden.
Select 1 correct option.
a True
b False
Ans: b

5. Q4
What will be printed when the following program is compiled and run?
class Super
{
public int getNumber( int a)
{
return 2;
}
}
public class SubClass extends Super
{
public int getNumber( int a, char ch)
{
return 4;
}
public static void main(String[] args)
{
System.out.println( new SubClass().getNumber(4) );
}
}
Select 1 correct option.
a 4
b 2
c It will not compile.
d It will throw an exception at runtime.
e None of the above.
Ans:b

6. Q5
Consider the contents of following two files:
//File A.java
package a;
public class A
{
A(){ }
public void print(){ System.out.println("A"); }
}
//File B.java
package b;
import a.*;
public class B extends A
{
B(){ }
public void print(){ System.out.println("B"); }
public static void main(String[] args)
{
new B();
}
}
What will be printed when you try to compile and run class B?
Select 1 correct option.
a It will print A.
b It will print B.
c It will not compile.
d It will compile but will not run.
e None of the above.
Ans:c

7. Q6
Consider the following code:
class Super
{
static{ System.out.print("super "); }
}
class One
{
static { System.out.print("one "); }
}
class Two extends Super
{
static { System.out.print("two "); }
}
class Test
{
public static void main(String[] args)
{
One o = null;
Two t = new Two();
}
}
What will be the output when class Test is run ?
Select 1 correct option.
a It will print one, super and two.
b It will print one, two and super.
c It will print super and two.
d It will print two and super
e None of the above.
Ans:c

8. Q7 What will the following code print when compiled and run?
class Base
{
void methodA()
{
System.out.println("base - MethodA");
}
}
class Sub extends Base
{
public void methodA()
{
System.out.println("sub - MethodA");
}
public void methodB()
{
System.out.println("sub - MethodB");
}
public static void main(String args[])
{
Base b=new Sub(); //1
b.methodA(); //2
b.methodB(); //3
}
}
Select 1 correct option.
a sub - MethodA , sub - MethodB
b base - MethodA , sub - MethodB
c Compile time error at //1
d Compile time error at //2
e Compile time error at //3 Ans: e

9. Q8
What will the following program print when run?
// Filename: TestClass.java
public class TestClass
{
public static void main(String args[] ){ A b = new B("good bye"); }
}
class A
{
A() { this("hello", " world"); }
A(String s) { System.out.println(s); }
A(String s1, String s2){ this(s1 + s2); }
}
class B extends A
{
B(){ super("good bye"); };
B(String s){ super(s, " world "); }
B(String s1, String s2){ this(s1 + s2 + " ! "); }
}
Select 1 correct option.
a It will print "good bye".
b It will print "hello world".
c It will print "good bye world".
d It will print "good bye" followed by "hello world".
e It will print "hello world" followed by "good bye". Ans: c

10. Q9
Which of the following access control keywords can be used to enable all the
subclasses to access a method defined in the base class?
Select 2 correct options
a public
b private
c protected
d No keyword is needed.
Ans:a,c

11. Q10
Consider the following class...
class MyString extends String
{
MyString(){ super(); }
}
The above code will not compile.
Select 1 correct option.
a True
b False
Ans:a

12. Q11
Which of the following method definitions will prevent overriding of that method?
Select 4 correct options
a public final void method m1()
b public static void method m1()
c public static final void method m1()
d public abstract void method m1()
e private void method m1()
Ans:a,b,c,e

13. Q12
Given the following classes, what will be the output of compiling and running the class
Truck?
class Automobile
{
public void drive() { System.out.println("Automobile: drive"); }
}
public class Truck extends Automobile
{
public void drive() { System.out.println("Truck: drive"); }
public static void main (String args [ ])
{
Automobile a = new Automobile();
Truck t = new Truck();
a.drive(); //1
t.drive(); //2
a = t; //3
a.drive(); //4
}
}
Select 1 correct option.
a Compiler error at line 3.
b Runtime error at line 3.
c It will print: Automobile: drive, Truck: drive, Automobile: drive, in that order.
d It will print: Automobile: drive, Truck: drive, Truck: drive, in that order.
e It will print: Automobile: drive, Automobile: drive, Automobile: drive, in that order.
Ans:d

14. Q13
What will be the result of attempting to compile and run the following program?
public class TestClass
{
public static void main(String args[ ] )
{
A o1 = new C( );
B o2 = (B) o1;
System.out.println(o1.m1( ) );
System.out.println(o2.i );
}
}
class A { int i = 10; int m1( ) { return i; } }
class B extends A {at int i = 20; int m1() { return i; } }
class C extends B { int i = 30; int m1() { return i; } }
Select 1 correct option.
a The progarm will fail to compile.
b Class cast exception runtime.
c It will print 30, 20.
d It will print 30, 30.
e It will print 20, 20. Ans: c

15. Q14
Consider the following code:
class A
{
A() { print(); }
void print() { System.out.println("A"); }
}
class B extends A
{
int i = Math.round(3.5f);
public static void main(String[] args)
{
A a = new B();
a.print();
}
void print() { System.out.println(i); }
}
What will be the output when class B is run ?
Select 1 correct option.
a It will print A, 4.
b It will print A, A
c It will print 0, 4
d It will print 4, 4
e None of the above. Ans: c

16. Q15
What will the following program print when run?
class Super
{
public String toString()
{
return "4";
}
}
public class SubClass extends Super
{
public String toString()
{
return super.toString()+"3";
}
public static void main(String[] args)
{
System.out.println( new SubClass() );
}
}
Select 1 correct option.
a 43
b 7
c It will not compile.
d It will throw an exception at runtime.
e None of the above. Ans: a