Wrapper class in Java

Java Tutorial

Java Tutorial Java Exercises Data Structures

Wrapper class in java are the Object representation of eight primitive types in java. All the wrapper classes in java are immutable and final. Java 5 autoboxing and unboxing allows easy conversion between primitive types and their corresponding wrapper classes in java programs.

Wrapper class in java provides the mechanism to convert primitive into object and object into primitive.

Since J2SE 5.0, autoboxing and unboxing feature converts primitive into object and object into primitive automatically. The automatic conversion of primitive into object is known as autoboxing and vice-versa unboxing.

The eight classes of java.lang package are known as wrapper classes in java. The list of eight wrapper classes.

Primitive TypeWrapper class
booleanBoolean
charCharacter
byteByte
shortShort
intInteger
longLong
floatFloat
doubleDouble
Example: Primitive to Wrapper

public class WrapperExample1
{  
public static void main(String args[])
{  
//Converting int into Integer  
int a=31;  
Integer i=Integer.valueOf(a);//converting int into Integer  
Integer j=a;//autoboxing, now compiler will write Integer.valueOf(a) internally  
  
System.out.println(a+" "+i+" "+j);  
}
}


Output:


31 31 31
Example: Wrapper to Primitive

public class WrapperExample2{    
public static void main(String args[]){    
//Converting Integer to int    
Integer a=new Integer(5);    
int i=a.intValue();//converting Integer to int  
int j=a;//unboxing, now compiler will write a.intValue() internally    
    
System.out.println(a+" "+i+" "+j);    
}}


Output:


5 5 5
Why do we need wrapper classes?

I think it was a smart decision to keep primitive types and Wrapper classes separate to keep things simple. We need wrapper classes when we need a type that will fit in the Object world programming like Collection classes. We use primitive types when we want things to be simple.

Primitive types can’t be null but wrapper classes can be null.

Wrapper classes can be used to achieve polymorphism.

Here is a simple program showing different aspects of wrapper classes in java.

Another Example: Wrapper classes

package com.journaldev.misc;

import java.util.ArrayList;
import java.util.List;

public class WrapperClasses {

    private static void doSomething(Object obj){
        
    }
    
    public static void main(String args[]){
        int i = 10;
        char c = 'a';
        
        //primitives are simple to use
        int j = i+3;
        
        //polymorphism achieved by Wrapper classes, we can't pass primitive here
        doSomething(new Character(c));
        
        List list = new ArrayList();
        //wrapper classes can be used in Collections
        Integer in = new Integer(i);
        list.add(in);
        
        //autoboxing takes care of primitive to wrapper class conversion
        list.add(j);
        
        //wrapper classes can be null
        in = null;
    }
}





Instagram


Java Programming