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:
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".
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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