java包装类 及其缓存
Java 包装类（Wrapper Class）是将基本数据类型转换为对象的方式，每个基本数据类型在 java.lang 包中都有一个相应的包装类：
-
Boolean对应基本类型boolean -
Character对应基本类型char -
Integer对应基本类型int -
Float对应基本类型float -
Double对应基本类型double -
Byte对应基本类型byte -
Short对应基本类型short -
Long对应基本类型long
包装类 自动拆箱 自动装箱
public static void main(String[] args) {// TODO Auto-generated method stubArrayList<Integer> list = new ArrayList<Integer>();list.add(Integer.valueOf(10));list.add(20);//自动装箱list.add(30);Integer firstElement= list.get(0);int firstPrimitive=list.get(0);//自动拆箱System.out.println("First element as an Integer: " + firstElement);System.out.println("First element as an int: "+ firstPrimitive);for (Integer integer : list) {System.out.println(integer);}}返回
First element as an Integer: 10
First element as an int: 10
10
20
30包装类缓存
public static void main(String[] args) {// TODO Auto-generated method stubInteger a=100;Integer b=100;System.out.println("a == b is "+ (a == b));//true 在缓存范围内 -128 -127System.out.println("a.equals(b) is "+ a.equals(b));//Integer c=200;Integer d=200;System.out.println("c == d is "+ (c == d));//falseSystem.out.println("c.euals(d) is "+ c.equals(d));//}返回
a == b is true
a.equals(b) is true
c == d is false
c.euals(d) is true