如何在 Java 中使用引用? [英] How to use references in Java?

问题描述

我想在 Java 中使用引用，但我不知道如何使用！例如在 C++ 中我们这样写:

I want to use reference in Java but I don't know how! for example in C++ we write:

void sum(int& x)
{
    ...
}

但在 Java &标志是编译器错误！请帮助我理解 Java 中的引用.

but in Java & sign is a compiler error! please help me to understand references in Java.

推荐答案

对象默认通过引用传递 对象通过引用访问，但是没有办法创建对原始值(byte、short、int、long)的引用.您必须创建一个对象来包装整数或使用单个元素数组.

Objects are passed by reference by default Objects are accessed by reference, but there is no way to create a reference to a primitive value (byte, short,int, long). You either have to create an object to wrap the integer or use a single element array.

public void sum(int[] i){
   i[0] = ...;
}

或

public void sum(MyInt i){
   i.value = ...;
}
public class MyInt{
   public int value; 
}

对于您的示例，以下内容可以工作

for your example something like the following could work

public int sum(int v){
   return ...;
}

或

public int sum(){
   return ...;
}

更新:

对象引用的附加/更好的描述:

Additional/Better description of object references:

Java 对象总是通过引用访问.与原始类型一样，此引用按值传递(例如复制).由于程序员在 java 中可以访问的所有内容(引用、原语)都是通过复制传递的，并且无法创建对原语类型的引用，因此对方法参数(引用、原语)的任何修改只会影响方法.对象可以在一个方法中修改，因为引用的两个副本(本地和其他)仍然指向同一个对象实例.

Java Objects are always accessed by a reference. Like the primitive types this reference is passed by value (e.g. copied). Since everything a programmer can access in java is passed by copying it (references, primitives) and there is no way to create a reference to a primitive type, any modification to a method parameter (references, primitives) only affects the local copy within the method. Objects can be modified within a method since both copies of the reference (local and other) still point to the same object instance.

示例:

在方法内修改一个原语，这只影响i的内部副本，而不影响传递的值.

Modify a primitive within method, this only affects the internal copy of i and not the passed value.

void primitive(int i){
  i = 0;
}

修改方法内的引用，这只影响引用的内部副本，而不影响传递的值.

Modify a reference within method, this only affects the internal copy of ref and not the passed value.

 void reference(Object ref){
    ref = new Object();//points to new Object() only within this method
 }

修改一个对象，全局可见

Modify an object, visible globally

void object(List l){
   l.add(new Object());//modifies the object instead of the reference
}

上面的数组和MyInt都是基于一个对象的修改.

Both the array and MyInt above are based on the modification of an object.

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