Wrapper Classes


What is a wrapper class?

A wrapper class is a class whose object wraps around a basic primitive data types. When we create an object to a wrapper class, it contains a field which could store a primitive data type.

Why do we need a wrapper class?

  • Primitive types doesn’t allow to store “null” as a value which is possible through a wrapper class.
  • Java Collection API stores only object, not primitive types.
  • An object is needed to support synchronization in multi-threading.

Wrapper classes in Java

Primitive data typesWrapper Class
byteByte
shortShort
intInteger
longLong
floatFloat
doubleDouble
booleanBoolean
charCharacter

Wrapper classes are immutable in Java

All primitive wrapper classes are immutable in Java, so operations like addition/subtraction results in a new object instead of modifying the old object.

package wrapper;

public class Immutability {
    public static void main(String[] args) {
        Integer num = new Integer("100");
        System.out.println("Number before increment: " + num);

        increment(num);

        System.out.println("Number after increment: " + num);
    }

    private static void increment(Integer num) {
        num += 1;
    }
}

Output of the above program –

Number before increment: 100
Number after increment: 100

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