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：

1. Boolean 对应基本类型 boolean

2. Character 对应基本类型 char

3. Integer 对应基本类型 int

4. Float 对应基本类型 float

5. Double 对应基本类型 double

6. Byte 对应基本类型 byte

7. Short 对应基本类型 short

8. Long 对应基本类型 long

 

包装类 自动拆箱 自动装箱

java">	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		ArrayList<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

java">First element as an Integer: 10
First element as an int: 10
10
20
30

包装类缓存

java">	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Integer a=100;
		Integer b=100;
	
		System.out.println("a == b is "+ (a == b));//true 在缓存范围内 -128 -127
		System.out.println("a.equals(b) is "+ a.equals(b));//
		
		Integer c=200;
		Integer d=200;
		System.out.println("c == d is "+ (c == d));//false
		System.out.println("c.euals(d) is "+ c.equals(d));//
	}

返回

java">a == b is true
a.equals(b) is true
c == d is false
c.euals(d) is true