比较Java中相互引用的对象

Question

int i = 0;
int j = i;
System.out.println("initial int: " + j); // 0

Integer ii = new Integer(0);
Integer jj = ii;
System.out.println("initial Integer: " + jj); // 0

String k = new String("s");
String l = k;
System.out.println("initial String: " + l); // "s"

Person person1 = new Person("Furlando"); // from constructor -> publ. instance var. 'name'
Person person2 = person1;
System.out.println("initial Person: " + person2.name); // "Furlando"

/*--------------------*/
System.out.println();
/*--------------------*/

i += 1;
System.out.print("added 1 to int: [" + i);
System.out.println("], and primitive which also \"refers\" to that (has a copy, actually), has a value of: [" + j + "]");

ii += 1;
System.out.print("added 1 to Integer object: [" + ii);
System.out.println("], and object which also refers to that, has a value of: [" + jj + "]");

k += "tring";
System.out.print("added \"s\" to String object: [" + k);
System.out.println("], and object which also refers to that, has a value of: [" + l + "]");

person1.name = "Kitty";
System.out.print("changed instance variable in Person object to: [" + person1.name);
System.out.println("], and object which also refers to that, has a value of: [" + person2.name + "]");

/* [COMPILER OUTPUT]
    initial int: 0
    initial Integer: 0
    initial String: s
    initial Person: Furlando

    A) added 1 to int: [1], and primitive which also "refers" to that (has a copy, actually), has a value of: [0]
    B) added 1 to Integer object: [1], and object which also refers to that, has a value of: [0]
    C) added "s" to String object: [string], and object which also refers to that, has a value of: [s]
    D) changed instance variable in Person object to: [Kitty], and object which also refers to that, has a value of: [Kitty]
*/

我理解A，我们在那里有一个原语；没有引用。by-复制。
我希望B和C的行为与D相同——根据它们被给予的引用而改变。

为什么这个对象引用另一个对象只对用户定义的对象“起作用”，而不是整数、字符串等。？

Answer 1

匿名用户

这与操作员的工作有关。

您真正在做的是在调用=时重新分配值

Integer i = 1;
Integer j = i;
i = i + 1;

因此，现在i指向另一个等于2的整数，j仍然指向原来的整数。

您的字符串示例也是如此。

在对象的情况下，不更改指针，而是更改对象的内部状态。因此，person1和person2都指向同一个人。

如果你做到了

Person person1 = new Person("Alice");
Person person2 = person1;
person1 = new Person("Bob");

那么很明显，person1现在是一个不同的人了。

Answer 2

这种行为与用户定义的对象与内部对象无关，但事实上，“Integer”和“String”（以及所有其他基本包装器）对象的处理非常特殊。整数只是一个围绕原始整数的“包装器”，因此它的行为不是真正的“引用类型”。所有这些包装器对象都实现为不可变的-对整数的相同引用永远不会有其他值。

另一方面，如果需要，这些包装器对象会自动转换为基本类型，因此它们的一般使用速度较慢。它们的好处是，它们可以为null，这有时很好。

Answer 3

在Java中，String和Integer对象是不可变的。当您这样做时：ii=1或创建新对象。变量jj和l指向旧对象。这就是为什么你会看到不同的价值观。