Java如何使用方法更改引用？

Question

我试图更改对象的引用，并编写了以下代码

public class Test {
    public static void main(String[] args) {
        Foo foo1 = new Foo();
        Foo foo2 = new Foo();
        System.out.println("the reference of foo1 is " + foo1);
        System.out.println("the reference of foo2 is " + foo2);
        System.out.println();
        change(foo1, foo2);
        System.out.println("the reference of foo1 is " + foo1);
        System.out.println("the reference of foo2 is " + foo2);
    }

    public static void change(Foo foo1, Foo foo2) {
        System.out.println("the reference of foo1 is " + foo1);
        System.out.println("the reference of foo2 is " + foo2);
        System.out.println();
        foo1 = foo2;
        System.out.println("the reference of foo1 is " + foo1);
        System.out.println("the reference of foo2 is " + foo2);
        System.out.println();
    }
}

class Foo {
    public Foo() {
        // do nothing
    }
}

我得到了以下输出

the reference of foo1 is Foo@15db9742
the reference of foo2 is Foo@6d06d69c

the reference of foo1 is Foo@15db9742
the reference of foo2 is Foo@6d06d69c

the reference of foo1 is Foo@6d06d69c
the reference of foo2 is Foo@6d06d69c

the reference of foo1 is Foo@15db9742
the reference of foo2 is Foo@6d06d69c

change方法在change方法中将foo1的引用从Foo@15db9742更改为Foo@6d06d69c，但在main方法中foo1的引用没有更改。为什么?

Answer 1

在Java中，方法的所有参数都是按值传递的。注意，作为对象引用的非原语类型的变量也按值传递：在这种情况下，引用按值传递

因此，在您的情况下，您在函数中所做的修改不会改变主函数中使用的对象