How to modify enum passed into Java method

Question

public class Test {
    private Result result;

    public Test(Result res){
        this.result = res;
    }

    public void alter(){
        this.result = Result.FAIL;
    }
}

public enum Result{ PASS, FAIL, MORE};
public Result myResult = Result.PASS;

Test test = new Test(myResult);
test.alter();

In the above example, how would I modify the variable myResult inside the alter method? Since Java is pass by value, the example simply assigns its value to this.result.

It was here: http://stackoverflow.com/questions/3997518/passing-enums-by-ref-in-java — lukastymo, Feb 17 '11 at 15:13

Stephen C · Accepted Answer · 2011-02-17T15:17:13.703

4

Basically, you can't, because Java is pass-by-value.

The closest you can get to pass-by-reference behavior in Java is to create a "holder" class with a getter and setter; e.g.

public class ResultHolder {
    private Result value;
    public ResultHolder(Result initial) { value = initial; }
    public void setValue(Result newValue) { value = newValue; }
    public Result getValue() { return value; }
}

Then, you could write alter() as:

public void alter(ResultHolder holder, Result newValue) {
    holder.setValue(newValue);
}

Note that this is not real pass-by-reference.

edited Feb 17 '11 at 15:17

answered Feb 17 '11 at 15:11

Stephen C

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Thanks, I considered putting it inside an object but wondered if there was some other way to fudge it. – Gorgon Feb 17 '11 at 15:25

score 3 · Answer 2 · answered Feb 17 '11 at 15:13

3

You can't modify the actual enum values. They're essentially classes that are named constants. If you want altered behavior inside an enum instance then you don't want an enum ( if you can alter the object then other consumers of the object can't treat it as a constant).

answered Feb 17 '11 at 15:13

Steve B.

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+1 This is the real answer. If you are trying to change an enum argument, then you don't want an enum to begin with. – Andres F. Jan 17 '12 at 01:33

score 0 · Answer 3 · answered Feb 17 '11 at 15:10

0

Simply put, you can't do it in Java.

answered Feb 17 '11 at 15:10

mdrg

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score 0 · Answer 4 · answered Feb 17 '11 at 15:12

0

Since myResult is the class field you can change it when you wish by assigning other value: myResult = Result.MORE;. it does not matter where do you write this code.

answered Feb 17 '11 at 15:12

AlexR

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score 0 · Answer 5 · answered Feb 17 '11 at 15:24

public class Test {
    private Result result;

    public Test(Result res){
        this.result = res;
    }

    public Result alter(){          // signature changed
        this.result = Result.FAIL;
        return this.result;         // new
    }
}

_

public enum Result{ PASS, FAIL, MORE};
public Result myResult = Result.PASS;

Test test = new Test(myResult);
myResult = test.alter();            // change the value

How to modify enum passed into Java method

5 Answers5