InstanceOfJava

Method overloading interview questions java

Posted by: Instanceofjava Posted date: 12:33 PM / comment : 0 Core java Interview Questions

1.What is Method in java?

Method is a sub block of a class that contains logic of that class.
logic must be placed inside a method, not directly at class level, if we place logic at class level compiler throws an error.
So class level we are allowed to place variables and methods.
The logical statements such as method calls, calculations and printing related statements must be placed inside method, because these statements are considered as logic.
For more information @ Methods in java

package com.instanceofjava;
class sample{
int a;
int b;
System.out.println("instance of java"); // compiler throws an error.
}

package com.instanceofjava;
class sample{
static int a=10;
public static void main(String args[]){

System.out.println(a); // works fine,prints a value:10

}
}

2.What is meant by method overloading in java?

Defining multiple methods with same name is known as polymorphism.
Defining multiple methods with same name and with different arguments known as method overloading.

package com.instanceofjava;
class A{
public void show(int a){
System.out.println("saidesh");
}
public void show(int a,int b){
System.out.println("ajay");
}
public void show(float a){
System.out.println("vinod");
}
public static void main(String args[]){
A a=new A();
a.show(10);
a.show(1,2);
a.show(1.2);
}
}

Output:

saidesh
ajay
vinod

3.What are the other names for method overloading?

Method overloading also known as static polymorphism or compile time polymorphism because at compile time itself we can tell which method going to get executed based on method arguments.
So method overloading also called as static binding.

4.What are the basic rules of method overloading?

Defining a method with same name and differ in number of arguments
Defining a method with same name and differ in type of arguments
Defining a method with same name and differ in order of type of arguments
Return type of the method not involved in method overloading.

5.Can we overload static methods in java?

Yes. We can overload static methods in java.
Method overriding is not possible but method overloading is possible for static methods.
Before that lets see about method overloading in java.

lets see an example java program which explains static method overloading.

class StaticMethodOverloading{
public static void staticMethod(){
System.out.println("staticMethod(): Zero arguments");
}
public static void staticMethod(int a){
System.out.println("staticMethod(int a): one argument");
}
public static void staticMethod(String str, int x){
System.out.println("staticMethod(String str, int x): two arguments");
}
public static void main(String []args){
StaticMethodOverloading.staticMethod();
StaticMethodOverloading.staticMethod(12);
StaticMethodOverloading.staticMethod("Static method overloading",10);
}
}

Output:

staticMethod(): Zero arguments
staticMethod(int a): one argument
staticMethod(String str, int x): two arguments

6.Can we overload main method in java?

Yes we can overload main method in java

Java Program to overload main method in java

class mainMethodOverloading{
public static void main(boolean x){
System.out.println("main(boolean x) called ");
}
public static void main(int x){
System.out.println("main(int x) called");
}
public static void main(int a, int b){
System.out.println("main(int a, int b) called");
}
public static void main(String []args){
System.out.println("main(String []args) called ");
mainMethodOverloading.main(true);
mainMethodOverloading.main(10);
mainMethodOverloading.main(37,46);
}
}

Output:

main(String []args) called
main(boolean x) called
main(int x) called
main(int a, int b) called

7.Can we overload constructors in java?

Yes we can overload constructor in java

package instanceofjava;
class ConstructorChaining{
int a,b
ConstructorChaining(){
this(1,2);
System.out.println("Default constructor");
}
ConstructorChaining(int x , int y){
this(1,2,3);
a=x;
b=y;
System.out.println("Two argument constructor");
}
ConstructorChaining(int a , int b,int c){
System.out.println("Three argument constructor")
}
public static void main(String[] args){
ConstructorChaining obj=new ConstructorChaining();
System.out.println(obj.a);
System.out.println(obj.b);
}
}

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Iterate through keys of hashtable java

Posted by: Instanceofjava Posted date: 11:28 AM / comment : 0 Hashtable , java Collections interview Questions

1.Basic java example program to iterate keys of hashtable

Enumeration keys() This method used to get keys of hashmap

package com.iteartekeysHashtable;
import java.util.Hashtable;
import java.util.Enumeration;
public class HashtableExample{
public static void main(String[] args) {
//create Hashtable object
Hashtable<String,String> hashtable = new Hashtable<String,String>();
//add key value pairs to Hashtable
hashtable.put("1","Java Interview Questions");
hashtable.put("2","Java Interview Programs");
hashtable.put("3","Concept and exampe program");
hashtable.put("4","Concept and interview Questions");
hashtable.put("5","Java Quiz");
hashtable.put("6","Real time examples");
Enumeration e=hashtable.keys();
// display search result
while (e.hasMoreElements()) {
System.out.println(e.nextElement());
}
}
}

Output:

Check particular value exist in hashtable

Posted by: Instanceofjava Posted date: 11:13 AM / comment : 0 Hashtable , java Collections interview Questions

1.Basic java example program to check particular value exist in hashtable

boolean contains(Object value) This method used to check particular value exist in hashtable

package com.CheckElelemtHashtable;
import java.util.Hashtable;
import java.util.Enumeration;
public class HashtableExample{
public static void main(String[] args) {
//create Hashtable object
Hashtable<String,String> hashtable = new Hashtable<String,String>();
//add key value pairs to Hashtable
hashtable.put("1","Java Interview Questions");
hashtable.put("2","Java Interview Programs");
hashtable.put("3","Concept and exampe program");
hashtable.put("4","Concept and interview Questions");
hashtable.put("5","Java Quiz");
hashtable.put("6","Real time examples");
/*
To check whether a particular value exists in Hashtable we need to use
boolean containsKey(Object value) method of Hashtable class.
if the Hashtable contains mapping for specified value It returns true
otherwise returns false.
*/
boolean isExists = hashtable.contains("Java Quiz");
System.out.println("Java Quiz exists in Hashtable ? : " + isExists);
System.out.println("Hashtable values : ");
Enumeration e=hashtable.elements();
// display search result
while (e.hasMoreElements()) {
System.out.println(e.nextElement());
}
}
}

Output:

Java Quiz exists in Hashtable ? : true
Hashtable values :
Real time examples
Java Quiz
Concept and interview Questions
Concept and exampe program
Java Interview Programs
Java Interview Questions

Check if a particular key exists in Java Hashtable example

Posted by: Instanceofjava Posted date: 11:04 AM / comment : 0 Hashtable , java Collections interview Questions

1.Basic java example program to check particular element exist in hashtable.

boolean containsKey(Object key) This method used to check particular key exist in hashtable

package com.CheckElelemtHashtable;
import java.util.Hashtable;
import java.util.Iterator;
public class HashtableExample{
public static void main(String[] args) {
//create Hashtable object
Hashtable<String,String> hashtable = new Hashtable<String,String>();
//add key value pairs to Hashtable
hashtable.put("1","Java Interview Questions");
hashtable.put("2","Java Interview Programs");
hashtable.put("3","Concept and exampe program");
hashtable.put("4","Concept and interview Questions");
hashtable.put("5","Java Quiz");
hashtable.put("6","Real time examples");
/*
To check whether a particular key exists in Hashtable we need to use
boolean containsKey(Object key) method of Hashtable class.
if the Hashtable contains mapping for specified key It returns true
otherwise returns false.
*/
boolean isExists = hashtable.containsKey("5");
System.out.println("5 exists in Hashtable ? : " + isExists);
Enumeration e=hashtable.elements();
System.out.println("Display result:");
// display search result
while (e.hasMoreElements()) {
System.out.println(e.nextElement());
}
}
}

Output:

5 exists in Hashtable ? : true
Hashtable values :
Display result:
Real time examples
Java Quiz
Concept and interview Questions
Concept and exampe program
Java Interview Programs
Java Interview Questions

Non static blocks in java example

Posted by: Instanceofjava Posted date: 4:47 PM / comment : 5 Core java Interview Questions

Non Static Blocks in java

When ever object created non static blocks will be executed before the execution of constructor
Non static blocks are class level block which does not have prototype

package nonstaticblocks;
public class A {
{
System.out.println("non static block executed");
}
}

What is the need of Non static blocks in java?

To execute any logic whenever object is created irrespective of constructor used in object creation.

Who will execute Non static blocks?

Non static blocks are automatically called by JVM for every object creation in java stack area

How many Non static blocks we can create?

We can create any number of Non static blocks

Order of execution of non static blocks

Order of execution of non static blocks will be order as they are defined.

package nonstaticblocks;
public class A {
{
System.out.println("first block");
}
{
System.out.println("second block");
}
{
System.out.println("third block");
}
public static void main(String[] args) {
A obj= new A();
}
}

Output:

first block
second block
third block

Order of execution of non static blocks with respect to constructor?

non static blocks in java example program

Remove all elements LinkedHashSet example

Posted by: Instanceofjava Posted date: 4:11 PM / comment : 0 java Collections interview Questions , LinkedHashSet

1.Basic java example program to remove all elements in linkedhashset

clear() This method used to remove all elements from Linkedhashset.

package com.removeelementLinkedhashset;
import java.util.LinkedHashSet;
import java.util.Iterator;
public class LinkedHashsetExample{
public static void main(String[] args) {
LinkedHashSet<String> linkedhashset = new LinkedHashSet<>();
linkedhashset.add("Java Interview Questions");
linkedhashset.add("Java interview program");
linkedhashset.add("Concept and example program");
linkedhashset.add("Concept and interview questions");
linkedhashset.add("Java Quiz");
System.out.println("LinkedHashSet before removal : " + linkedhashset);
boolean blnRemoved = linkedhashset.remove("Java Quiz");
System.out.println("Was Java Quiz removed from LinkedHashSet ? " + blnRemoved);
System.out.println("LinkedHashSet after removal : ");
Iterator it=linkedhashset.iterator();
while(it.hasNext()){
System.out.println(it.next());
}
linkedhashset.clear();
System.out.println("LinkedHashSet after removal all elements");
}
}

Output:

LinkedHashSet before removal : [Java Interview Questions, Java interview program, Concept
and example program, Concept and interview questions, Java Quiz]
Was Java Quiz removed from LinkedHashSet ? true
LinkedHashSet after removal :
Java Interview Questions
Java interview program
Concept and example program
Concept and interview questions
LinkedHashSet after removal all elements :[]

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