Whether Java is a value pass or a reference pass

First write a simple employee to test the use.

class Employee {    private  String name;      Public Employee (String name) {        this. Name = name;    }       Public String GetName () {        return  name;    }      Public void setName (String name) {        this. Name = name;    }} 

Then write a function, pass in a Emplyee object, modify the name, if the function completes the original employee's name value changes, according to our understanding, will be considered as a reference pass.

 Public Static void Main (string[] args) {        new Employee ("Alice");         New Employee ("Bob");        ChangeName (a);        System.out.println (A.getname ());        System.out.println (B.getname ());    }      Public Static void changename (Employee x) {        x.setname ("Fly");    }

Execution Result:

Fly
Bob

But there is also a test case that swaps two of objects. If a reference is passed, the name of the two object is exchanged after the function execution finishes. Let's try it now.

 Public Static void Main (string[] args) {        new Employee ("Alice");         New Employee ("Bob");        Swap (A, b);        System.out.println (A.getname ());        System.out.println (B.getname ());    }      Public Static void Swap (employee x, employee y)    {        = x;         = y;         = t;    }

Execution Result:

Alice
Bob

But they have not changed anything. What's the situation?! Has it become a value transfer?

The final answer is indeed a value pass . The first example gives you the feeling that a reference is passed because the value of the incoming function is a copy of the object reference. (the phrase in C is a copy of a pointer, that is, a copy of the address.) ）

At this point, we'll write the last example, modifying the name value of x in the swap function.

 Public Static void Swap (employee x, employee y)    {        = x;         = y;         = T;        X.setname ("Joyce");    

Execution Result:

Alice
Joyce

See, the X-Exchange reference is B, so after modifying X, B changes. The second time because there is no modification, the function after the end of nothing, after all, just a copy of the reference ~

Java is a value pass, and a value is a copy of an object reference.

Whether Java is a value pass or a reference pass