Java通过引用传递 [英] Java pass by reference

问题描述

这两个代码有什么区别：

What is the difference between this 2 codes:

代码A：

Foo myFoo;
myFoo = createfoo();

其中

public Foo createFoo()
{
   Foo foo = new Foo();
   return foo;
}

Vs。代码B：

Foo myFoo;
createFoo(myFoo);

public void createFoo(Foo foo)
{
   Foo f = new Foo();
   foo = f;
}

这2个代码之间是否有任何差异？

Are there any differences between these 2 pieces of codes?

推荐答案

Java总是按值而不是通过引用传递参数。

Java always passes arguments by value NOT by reference.

让我通过示例解释一下：

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");
     }
}

我将分步说明：

1. 声明类型为 Foo的名为 f 的引用并将其分配给类型为 Foo 的新对象，其属性为f。

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");

从方法方面，类型为 Foo 的引用声明名称 a ，并且它最初被分配给 null 。

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)

当你调用方法 changeReference ，引用 a 将被分配给作为参数传递的对象。

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

changeReference(f);

声明类型为<$ c的名为 b 的引用$ c> Foo 并将其分配给类型为 Foo 的新对象，其属性为b。

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 正在重新分配参考 a NOT f 到属性为b的对象。

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

当您调用 modifyReference（Foo c）方法时，a引用 c 已创建并分配给属性为f的对象。

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

c.setAttribute（c）; 将更改引用 c 点的对象的属性对它来说，引用 f 指向它是同一个对象。

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.

我希望您现在了解如何将对象作为参数传递在Java中：）

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

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