Java学习随笔1:Java是值传递还是引用传递?

java

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:

  1. 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");

  2. 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)

  3. As you call the method changeReference, the reference a will be assigned to the object which is passed as an argument.

    changeReference(f);

  4. 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");

  5. a = b is re-assigning the reference a NOT f to the object whose its attribute is "b".


  6. As you call modifyReference(Foo c) method, a reference c is created and assigned to the object with attribute "f".

  7. 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 :)

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