Java Wrapper Classes

Wrapper class helps to use primitive data types (int, char, boolean, etc.) as objects. The below table shows the primitive data types and the equivalent wrapper classes:

When working with Collection objects, such as ArrayList, we use Wrapper Classes (the primitive types cannot be used). The List can only use objects.

Example

ArrayList<int> numbers = new ArrayList<int>(); // Invalid
ArrayList<Integer> numbers = new ArrayList<Integer>(); // Valid

Creating Wrapper Objects

To create a wrapper object, use the wrapper class instead of primitive type. To get the value of the object, we just print the object.

Example

public class WrapperObject {
       public static void main (String args[]){
              Integer myInt = 100;
              Double myDouble = 9.999;
              Character myChar = 'R';
             
              System.out.println(myInt);
              System.out.println(myDouble);
              System.out.println(myChar);
       }
}

Output

100
9.999
R

As we are now working with objects, we can use certain methods to get information about the specific object such as intValue(), charValue(), byteValue(), shortValue(), longValue(), floatValue(), doubleValue() and booleanValue() are associated with their corresponding wrapper classes.

The above example will output the same result as the example below:

Example

public class WrapperObject {
       public static void main (String args[]){
              Integer myInt = 100;
              Double myDouble = 9.999;
              Character myChar = 'R';
             
              System.out.println(myInt.intValue());
              System.out.println(myDouble.doubleValue());
              System.out.println(myChar.charValue());
       }
}

Output

100
9.999
R

Convert Wrapper Objects to Strings

We can convert wrapper objects to Strings using toString() method.

Example

In the below example, we convert an Integer to a String and we use the length() method of the String class to output the length of the String:

public class WrapperObject {
       public static void main (String args[]){
              Integer myInt = 10000;
             
              String myString = myInt.toString(); //Convert Integer to String
              System.out.println(myString.length()); //Length of the String
             
       }
}

Output

5