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Java Interview Questons and Answers
What is the output for the below code ?
1. public
class A {
2. int
add(int i, int j){
3. return
i+j;
4. }
5.}
6.public
class B extends A{
7. public
static void main(String argv[]){
8. short s
= 9;
9.
System.out.println(add(s,6));
10. }
11.}
Options are
A.Compile
fail due to error on line no 2
B.Compile
fail due to error on line no 9
C.Compile
fail due to error on line no 8
D.15
Answer :
B is the
correct answer.
Cannot make
a static reference to the non-static method add(int, int) from the type A. The
short s is
autoboxed correctly, but the add() method cannot be invoked from a static
method
because add() method is not static
What is the output for the below code ?
public
class A {
int k;
boolean
istrue;
static int
p;
public void
printValue() {
System.out.print(k);
System.out.print(istrue);
System.out.print(p);
}
}
public
class Test{
public
static void main(String argv[]){
A a = new
A();
a.printValue();
}
}
Options are
A.0 false 0
B.0 true 0
C.0 0 0
D.Compile
error - static variable must be initialized before use.
Answer :
A is the
correct answer.
Global and
static variable need not be initialized before use. Default value of global and
static int
variable is zero. Default value of boolean variable is false. Remember local
variable
must be initialized before u
What is the output for the below code ?
public
class Test{
int _$;
int $7;
int do;
public
static void main(String argv[]){
Test test =
new Test();
test.$7=7;
test.do=9;
System.out.println(test.$7);
System.out.println(test.do);
System.out.println(test._$);
}
}
Options are
A.7 9 0
B.7 0 0
C.Compile
error - $7 is not valid identifier.
D.Compile
error - do is not valid identifier.
Answer :
D is the
correct answer.
$7 is valid
identifier. Identifiers must start with a letter, a currency character ($), or
underscore
( _ ). Identifiers cannot start with a number. You can't use a Java keyword as
an
identifier. do is a Java keyword.
What is the output for the below code ?
package
com;
class
Animal {
public void
printName(){
System.out.println("Animal");
}
}
package
exam;
import
com.Animal;
public
class Cat extends Animal {
public void
printName(){
System.out.println("Cat");
}
}
package
exam;
import
com.Animal;
public
class Test {
public
static void main(String[] args){
Animal a =
new Cat();
a.printName();
}
}
Options are
A.Animal
B.Cat
C.Animal
Cat
D.Compile
Error
Answer :
D is the
correct answer.
Cat class
won't compile because its superclass, Animal, has default access and is in a
different
package. Only public superclass can be accessible for different package.
What is the output for the below code ?
public
class A {
int i = 10;
public void
printValue() {
System.out.println("Value-A");
};
}
public
class B extends A{
int i = 12;
public void
printValue() {
System.out.print("Value-B");
}
}
public
class Test{
public
static void main(String argv[]){
A a = new
B();
a.printValue();
System.out.println(a.i);
}
}
Options are
A.Value-B
11
B.Value-B
10
C.Value-A
10
D.Value-A
11
Answer :
B is the
correct answer.
If you
create object of subclass with reference of super class like ( A a = new B();)
then
subclass
method and super class variable will be executed.
What is the output for the below code ?
public enum
Test {
BREAKFAST(7,
30), LUNCH(12, 15), DINNER(19, 45);
private int
hh;
private int
mm;
Test(int
hh, int mm) {
assert (hh
>= 0 && hh <= 23) : "Illegal hour.";
assert (mm
>= 0 && mm <= 59) : "Illegal mins.";
this.hh =
hh;
this.mm =
mm;
}
public int
getHour() {
return hh;
}
public int
getMins() {
return mm;
}
public
static void main(String args[]){
Test t =
new BREAKFAST;
System.out.println(t.getHour()
+":"+t.getMins());
}
}
Options are
A.7:30
B.Compile
Error - an enum cannot be instantiated using the new operator.
C.12:30
D.19:45
Answer :
B is the
correct answer.
As an enum
cannot be instantiated using the new operator, the constructors cannot be
called
explicitly. You have to do like Test t = BREAKFAST;
What is the output for the below code ?
public
class A {
static{System.out.println("static");}
{
System.out.println("block");}
public A(){
System.out.println("A");
}
public
static void main(String[] args){
A a = new
A();
}
Options are
A.A block
static
B.static
block A
C.static A
D.A
Answer :
B is the
correct answer.
First
execute static block, then statement block then constructor.
What is the output for the below code ?
1. public
class Test {
2. public
static void main(String[] args){
3. int i =
010;
4. int j =
07;
5.
System.out.println(i);
6.
System.out.println(j);
7. }
8. }
Options are
A.8 7
B.10 7
C.Compilation
fails with an error at line 3
D.Compilation
fails with an error at line 5
Answer :
A is the
correct answer.
By placing
a zero in front of the number is an integer in octal form. 010 is in octal form
so its
value is 8.
What is the output for the below code ?
1. public
class Test {
2. public
static void main(String[] args){
3. byte b =
6;
4. b+=8;
5.
System.out.println(b);
6. b = b+7;
7.
System.out.println(b);
8. }
9. }
Options are
A.14 21
B.14 13
C.Compilation
fails with an error at line 6
D.Compilation
fails with an error at line 4
Answer :
C is the
correct answer.
int or
smaller expressions always resulting in an int. So compiler complain about Type
mismatch:
cannot convert from int to byte for b = b+7; But b += 7; // No problem
because +=,
-=, *=, and /= will all put in an implicit cast. b += 7 is same as b =
(byte)b+7
so compiler
not complain.
What is the output for the below code ?
public
class Test {
public
static void main(String[] args){
String
value = "abc";
changeValue(value);
System.out.println(value);
}
public
static void changeValue(String a){
a =
"xyz";
}
}
Options are
A.abc
B.xyz
C.Compilation
fails
D.Compilation
clean but no output
Answer :
A is the
correct answer.
Java pass
reference as value. passing the object reference, and not the actual object
itself.
Simply
reassigning to the parameter used to pass the value into the method will do
nothing, because the
parameter is essentially a local variable.
