How to modify enum passed into Java method

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 t开发者_运维问答his.result.

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.

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).

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

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.

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