19_Wrapper_Class.md

Wrapper Class

Boxing and Unboxing, AutoBoxing

Intro

In Java, there are primitive data types and Wrapper classes

• Primitive data types: int, long, float, double, boolean, etc.
• Wrapper classes: Integer, Long, Float, Double, Boolean, etc.

Boxing & Unboxing

• Boxing

  • Converting a Primitive data type to a Wrapper class

    int n = 100;
    Integer num = new Integer(n);

• Unboxing

  • Converting a Wrapper class to a Primitive data type

    Integer num = new Integer(100);
    int n = num.intValue();

Auto Boxing

• Since JDK 1.5, the Java compiler automatically performs conversion when boxing and unboxing are needed -> Auto Boxing & Auto Unboxing

  • This feature is only available when there is a corresponding Primitive data type for each Wrapper class

    // Auto Boxing
    int n = 100;
    Integer num = n;
    
    // Auto Unboxing
    Integer num = new Integer(100);
    int n = num;

• Caution: Performance

  • Although Auto Boxing and Auto Unboxing are provided for convenience, since additional computation work is needed internally, it is better to implement same-type operations so that Auto Boxing & Auto Unboxing does not occur