Java 自动装箱和拆箱

Primitive type  Wrapper class
boolean         Boolean
byte            Byte
char            Character
float           Float
int         Integer
long            Long
short           Short
double          Double

class AutoboxingExample1
{
   public static void myMethod(Integer num){
    System.out.println(num);
   }
   public static void main(String[] args) {
       /* passed int (primitive type), it would be 
        * converted to Integer object at Runtime
        */
    myMethod(2);
   }
}

2

Integer inum = 3; //Assigning int to Integer: Autoboxing
Long lnum = 32L; //Assigning long to Long: Autoboxing

ArrayList<Integer> arrayList = new ArrayList<Integer>();
arrayList.add(11); //Autoboxing - int primitive to Integer
arrayList.add(22); //Autoboxing

class UnboxingExample1
{
   public static void myMethod(int num){
    System.out.println(num);
   }
   public static void main(String[] args) {

        Integer inum = new Integer(100);

        /* passed Integer wrapper class object, it 
         * would be converted to int primitive type 
         * at Runtime
         */
        myMethod(inum);
    }
}

100

Integer inum = new Integer(5);
int num = inum; //unboxing object to primitive conversion

ArrayList arrayList = new ArrayList()
int num = arrayList.get(0); // unboxing because get method returns an Integer object

Integer number = 100;

Integer number = Integer.valueOf(100);

Integer num2 = new Integer(50);
int inum = num2;

Integer num2 = new Integer(50);
int inum = num2.intValue();