Wrapper class in Java

  • Wrapper classes allow primitive data types to be accessed as objects and objects as a primitive data types.
  • The various wrapper classes for primitive data type are: Boolean, Byte, Character, Double, Float, Integer, Long and Short.
  • Wrapper classes make the primitive type data to act as objects.

Autoboxing

Autoboxing is the process of converting a primitive data type into corresponding wrapper class object. E.g. int to Integer.

Example: Sample program for autoboxing

class AutoBoxDemo
{  
    public static void main(String args[])
    {
        int x = 50;
        Integer y = Integer.valueOf(x);
        Integer z = x + y;
       System.out.println(x+"  "+y+"  "+z);
    }
}


Output:
50  50  100

Unboxing

Converting an object of wrapper class into corresponding primitive data type is known as unboxing. For example Integer to int.

Example: Sample program for unboxing

class UnBoxDemo
{  
    public static void main(String args[])
    {
        Integer x = new Integer(15);
        int y = x.intValue();
        int z = x * y;
        System.out.println(x+"  "+y+"  "+z);
    }
}


Output:
15  15  225

Primitive type and their corresponding wrapper class

Primitive typeWrapper class
booleanBoolean
byteByte
charCharacter
floatFloat
intInteger
longLong
shortShort
doubleDouble

Features of Wrapper class

  • Wrapper classes convert numeric strings into numeric values.
  • They provide a way to store primitive data into the object.
  • The valueOf() method is available in all wrapper classes except Character.
  • All wrapper classes have typeValue() method. This method returns the value of the object as its primitive type.

Character class method

isDigit(): to determine whether the character is digit.

isLower(): to determine whether the character is lower case alphabet.

isLetter(): to determine whether the character is an alphabet.

Byte class method

byteValue(): returns the Byte value as byte value.

parseByte(): returns byte value from a byte string.

Integer class method

intValue(): returns the Integer value as int value.

parseInt(): returns the int value from a int string.
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