Java中存在装箱与拆箱机制

• 装箱(Boxing)

  Integer I = 10;
  

• 拆箱(Unboxing)

  int i = I;
  

• 实际译为

  Integer I = Integer.valueOf(10);
  int i = I.intValue();
  

如果比较两个整数的包装类则发现

Integer i = new Integer(10);
Integer j = new Integer(10);
System.out.println(i == j); //false,因为对象是两个

Integer m = 10;
Integer n = 10;
System.out.println(m == n); //true,因为对象有缓存

Integer p = 200;
Integer q = 200;
System.out.println(p == q); //false,因为对象是两个

• 编译器会缓存[-128, 127]并且进行过装箱的整数，并进行拆箱

String对象的特殊性

• 判断相等，一定不要用==，要用equals
• 但是字符串常量(String literal)及字符串常量会进行内部化(interned)，相同的字符串常量是==的
  ``` String hello = “Hello”, lo = “lo”; System.out.println(hello == “Hello”); //true System.out.println(Other.hello == hello); //true

System.out.println(hello == (“Hel” + “lo”)); //true System.out.println(hello == (“Hel” + lo)); //false

System.out.println(hello == new String(“Hello”)); //false System.out.println(hello == (“Hel” + lo).intern()); //true ```