java 引用传递,Java通过引用传递

What is the difference between this 2 codes:

Code A:

Foo myFoo;

myFoo = createfoo();

where

public Foo createFoo()

{

Foo foo = new Foo();

return foo;

}

Vs. Code B:

Foo myFoo;

createFoo(myFoo);

public void createFoo(Foo foo)

{

Foo f = new Foo();

foo = f;

}

Are there any differences between these 2 pieces of codes?

解决方案

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 :)