Java学习随笔1：Java是值传递还是引用传递？

Java always passes arguments by value NOT by reference.

Let me explain this through an example:

public class Main{
public static void main(String[] args){
Foo f = new Foo("f");
changeReference(f); // It won't change the reference!
modifyReference(f); // It will modify the object that the reference variable "f" refers to!
}
public static void changeReference(Foo a){
Foo b = new Foo("b");
a = b;
}
public static void modifyReference(Foo c){
c.setAttribute("c");
}
}

I will explain this in steps:

Declaring a reference named

f

of type

Foo

and assign it to a new object of type

Foo

with an attribute

"f"

.

Foo f = new Foo("f");

From the method side, a reference of type

Foo

with a name

a

is declared and it's initially assigned to

null

.

public static void changeReference(Foo a)

As you call the method

changeReference

, the reference

a

will be assigned to the object which is passed as an argument.

changeReference(f);

Declaring a reference named

b

of type

Foo

and assign it to a new object of type

Foo

with an attribute

"b"

.

Foo b = new Foo("b");

a = b

is re-assigning the reference

a

NOT

f

to the object whose its attribute is

"b"

.



As you call

modifyReference(Foo c)

method, a reference

c

is created and assigned to the object with attribute

"f"

.

c.setAttribute("c");

will change the attribute of the object that reference

c

points to it, and it's same object that reference

f

points to it.



I hope you understand now how passing objects as arguments works in Java :)