InstanceOfJava

Boxing and unboxing in java

Posted by: Instanceofjava Posted date: 3:52 PM / comment : 0 Java SE

The concept of representing the primitive data values in the form of its equivalent and corresponding wrapper class objects is known as "boxing"

Integer x= new Integer(3);
Double d= new Double(1.2);
package com.instanceofjavaforus;

public class wraperDemo3 {
public static void main(String args[]){
        String s1="12";
        Integer i=new Integer(s1);
        System.out.println(i);

    }
}
The concept of getting back actual primitive data values present inside wrapper class objects into its corresponding primitive data value known as "unboxing"
Integer x= new Integer(3);
int y= x.intValue();
package com.instanceofjavaforus;

public class wraperDemo3 {

public static void main(String args[]){

            String s1="12";
            Integer i=new Integer(s1);
            int x=i.intValue();
            System.out.println(x);
        }
          }
The concept of JVM automatically representing the primitive data values in the form of its equivalent and corresponding wrapper class objects is known as "Autoboxing".

Integer x=3;
Double d= 1.3;
package com.instanceofjavaforus;
public class wraperDemo3 {
public static void main(String args[]){

    Integer x=3;
             Double d= 1.3;
            System.out.println(x);
            System.out.println(d);

            }
        }
The concept of getting back actual primitive data values present inside wrapper class objects into its corresponding primitive data value automatically by JVM known as "Autounboxing"
Integer x= new Integer(3);
int y= x;
package com.instanceofjavaforus;
public class wraperDemo3 {
public static void main(String args[]){

    Integer x= new Integer(3);
   int y= x;
            System.out.println(x);
            System.out.println(y);
            }
        }

Wrapper Classes

Posted by: Instanceofjava Posted date: 2:51 PM / comment : 0 Java SE

Using wrapper classes we can wrap the concept of object on the top of the primitive data.
And represent the primitive data values in the form of its equivalent objects.
In order to represent the 8 primitive data values in the form of its equivalent objects we have 8 wrapper classes they are
1. Byte
2. Short
3. Integer
4. Long
5. Double
6. Float
7. Character
8. Boolean

Uses of wrapper classes:

Using wrapper classes we can represent the primitive data values in form of its equivalent objects.
many time it would be required to represent the primitive data values in the form of objects
ex: Collections, Session
Wrapper classes supports the functions using which we can get back the sequence of primitive data characters present inside the string class object back into its corresponding data value.
It has two constructors
1. Accepts the values of primitive data
2. Accepts the object of String class
Syntax:
Integer num1=new Integer(12);
Integer num2=new Integer("12");
To get the value form it
int n=num2.intValue();

Integer wrapper class Example program:

package com.instanceofjavaforus;

public class wrapperDemo {

public static void main(String args[]){

    int x=12;

    Integer num1=new Integer(x);
    System.out.println(num1);
    num1=num1+1;
    System.out.println(num1);
    String str="12";
    Integer num2= new Integer(str);
    System.out.println(num2);

    int num3=num2.intValue();

    System.out.println(num3);
}

}

Output:

12
13
12
12

Example program 2 on Integer wrapper class:

package com.instanceofjavaforus;
public class Wraperdemo2 {
    public static void main(String args[]){

        String s1="12";
        Integer i=new Integer(s1);

        int x=i.intValue();

        System.out.println(x);
        String s2="abc";
        Integer i2=new Integer(s2);// no compilation error but run time error will come

        String s3=" 123";

        Integer i3= new Integer(s3);// run time error
        i3= new Integer(s3.trim());// recommended to trim
    }

}

String s2="abc"
Integer i2=new Integer(s2);// no compilation error but run time error will come.
It accepts String class object but the string should contain only integer otherwise the constructor dont know how to represent characters gives error.
String a=" 123";
here some times there may be a chance of having spaces in a string so it is recommended to trim the object
i3= new Integer(s3.trim());// recommended to trim

Program 3 :
package com.instanceofjavaforus;

public class wraperDemo3{
public static void main(String args[]){

        String s1="12";
        Integer i=new Integer(s1);

        int x=i.intValue();
        System.out.println(x);

        String s2="123";
        int y= Integer.parseInt(s2.trim());
    }
}
Output:
12

Print numbers in pyramid shape

Posted by: Instanceofjava Posted date: 2:12 PM / comment : 0 Java Programs

package com.instanceofjava;
public class Pyramidshape {
public static void main(String[] args) {
int num=10;
for (int i = 1; i < num; i++) {
for (int j = 1; j<=num-i;j++) {
System.out.print(" ");
}
for (int k = 1; k <= i; k++) {
System.out.print(""+k+" ");
}
for (int l =i-1; l >0; l--) {
System.out.print(""+l+" ");
}
System.out.println();
}
}

Output:

1
1 2 1
1 2 3 2 1
1 2 3 4 3 2 1

Sort object using comparator

Posted by: Instanceofjava Posted date: 7:18 PM / comment : 0 Java Programs

package com.instanceofjava;
public class Employee
{
int id;
String name;
public Employee(int id, String name) {
this.id=id;
this.name=name;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}

class MyEmpComp implements Comparator<Employee >
{
@Override
public int compare(Employee e1, Employee e2) {
if(e1.getName() < e2.getName()){
return 1;
} else {
return -1;
}
}
}

package com.oops;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.io.*;
class Main{
public static void main(String args[]){
ArrayList al=new ArrayList();
al.add(new Employee(101,"Indhu"));
al.add(new Employee(106,"Sindhu"));
al.add(new Employee(105,"Swathi"));
Collections.sort(al,MyEmpComp );
Iterator itr=al.iterator();
while(itr.hasNext()){
Employee st=(Employee)itr.next();
System.out.println(st.id +" "+st.name );
}
}
}

Output:

Indhu
Swathi
Sindhu

Sort object using comparable interface

Posted by: Instanceofjava Posted date: 7:15 PM / comment : 0 Java Programs

package com.instanceofjava;
import java.util.Comparable;
public class Employee implements Comparable<Employee> {
int id;
String name;
public Employee(int id, String name) {
this.id=id;
this.name=name;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public int compareTo(Employee e) {
Integer i= this.getId();
Integer j=e.getId();
if (this.getId() == e.getId())
return 0;
if (this.getId() < e.getId())
return 1;
if (this.getId() > e.getId())
return -1;
return 0;
}
}

package com.oops;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.io.*;
class Main{
public static void main(String args[]){
ArrayList al=new ArrayList();
al.add(new Employee(101,"Indhu"));
al.add(new Employee(106,"Sindhu"));
al.add(new Employee(105,"Swathi"));
Collections.sort(al);
Iterator itr=al.iterator();
while(itr.hasNext()){
Employee st=(Employee)itr.next();
System.out.println(st.id +" "+st.name );
}
}
}

Output:

Indhu
Swathi
Sindhu

Method overriding example program

Posted by: Instanceofjava Posted date: 7:09 PM / comment : 1 Java Programs

package com.oops;
class A
{
void msg(){
System.out.println("Hello");
}
}

class B extends A
{
void msg(){
System.out.println("Welcome");
}
public static void main(String args[])
{
A a=new A();
B b=new B();
A obj=new B();
System.out.println(a.msg()); // Hello
System.out.println(obj.msg()); // Welcome
System.out.println(b.msg()); //Welcome
}
}

Output:

Hello
Welcome
Welcome

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