java - 如何在 Java 中对原语执行相当于引用传递的操作

Question

这段Java代码:

public class XYZ {   
    public static void main(){  
        int toyNumber = 5;   
        XYZ temp = new XYZ();  
        temp.play(toyNumber);  
        System.out.println("Toy number in main " + toyNumber);  
    }

    void play(int toyNumber){  
        System.out.println("Toy number in play " + toyNumber);   
        toyNumber++;  
        System.out.println("Toy number in play after increement " + toyNumber);   
    }   
}  

将输出:

 Toy number in play 5  Toy number in play after increement 6  Toy number in main 5  

In C++ I can pass the toyNumber variable as pass by reference to avoid shadowing i.e. creating a copy of the same variable as below:

void main(){  
    int toyNumber = 5;  
    play(toyNumber);  
    cout << "Toy number in main " << toyNumber << endl;  
}

void play(int &toyNumber){  
    cout << "Toy number in play " << toyNumber << endl;   
    toyNumber++;  
    cout << "Toy number in play after increement " << toyNumber << endl;   
} 

C++ 输出将是这样的:

Toy number in play 5  Toy number in play after increement 6  Toy number in main 6  

我的问题是 - 假设 Java is pass by value rather than pass by reference 获得与 C++ 代码相同的输出，Java 中的等效代码是什么？ ？

Answer 1

您有多种选择。最有意义的实际上取决于您想要做什么。

选择 1:将 toyNumber 设为类中的公共(public)成员变量

class MyToy {
  public int toyNumber;
}

然后将对 MyToy 的引用传递给您的方法。

void play(MyToy toy){  
    System.out.println("Toy number in play " + toy.toyNumber);   
    toy.toyNumber++;  
    System.out.println("Toy number in play after increement " + toy.toyNumber);   
}

选择 2:返回值而不是通过引用传递

int play(int toyNumber){  
    System.out.println("Toy number in play " + toyNumber);   
    toyNumber++;  
    System.out.println("Toy number in play after increement " + toyNumber);   
    return toyNumber
}

此选择需要对 main 中的调用站点进行一些小更改，以便其显示为 toyNumber = temp.play(toyNumber);。

选择 3:将其设为类或静态变量

如果这两个函数是同一类或类实例上的方法，您可以将 toyNumber 转换为类成员变量。

选择 4:创建一个 int 类型的单元素数组并传递该数组

这被认为是一种黑客行为，但有时用于从内联类调用返回值。

void play(int [] toyNumber){  
    System.out.println("Toy number in play " + toyNumber[0]);   
    toyNumber[0]++;  
    System.out.println("Toy number in play after increement " + toyNumber[0]);   
}