How to do the equivalent of pass by reference for primitives in Java

Question

This Java code: ``` 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); } } ``` will output this: ``` 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; } ``` and the C++ output will be this: ``` Toy number in play 5 Toy number in play after increement 6 Toy number in main 6 ``` My…

Accepted Answer

You have several choices. The one that makes the most sense really depends on what you're trying to do.

Choice 1: make toyNumber a public member variable in a class

```
class MyToy {
  public int toyNumber;
}
```

then pass a reference to a MyToy to your method.

```
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);   
}
```

Choice 2: return the value instead of pass by reference

```
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
}
```

This choice would require a small change to the callsite in main so that it reads, `toyNumber = temp.play(toyNumber);`.

Choice 3: make it a class or static variable

If the two functions are methods on the same class or class instance, you could convert toyNumber into a class member variable.

Choice 4: Create a single element array of type int and pass that

This is considered a hack, but is sometimes employed to return values from inline class invocations.

```
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]);   
}
```

How to do the equivalent of pass by reference for primitives in Java

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