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();

哪里

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

对比.代码 B:

Foo myFoo;
createFoo(myFoo);

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

这两段代码有什么区别吗?

Are there any differences between these 2 pieces of codes?

推荐答案

Java 总是按值而不是按引用传递参数.

Java always passes arguments by value NOT by reference.

让我通过一个示例来解释:

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");
     }
}

我将分步解释:

1. 声明一个名为 f 的类型为 Foo 的引用，并将其分配给一个类型为 Foo 的新对象，并带有一个属性 "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");

在方法方面，声明了一个名为 a 的 Foo 类型的引用，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)

当您调用方法 changeReference 时，引用 a 将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);

声明一个名为 b 的类型为 Foo 的引用，并将它分配给一个类型为 Foo 的新对象，并带有一个属性 "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 正在将引用 a 而不是 f 重新分配给其属性为 的对象"b".

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，会创建一个引用 c 并将其分配给具有属性 "f" 的对象代码>.

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

c.setAttribute("c"); 将改变引用 c 指向它的对象的属性，并且引用 c 的对象是同一个对象code>f 指向它.

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.

我希望你现在明白在 Java 中如何将对象作为参数传递 :)

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

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