Mutable boolean field in Java

Question

I need a mutable boolean field in Java (I will return this field via get* method later and it should be possible to modify this field).

Boolean doesn't work because there are no set* methods in the Boolean class (I would say that Boolean is immutable, you can only change the reference, but you can't change the object itself).

I guess I can use Boolean array of size 1. But probably there are more elegant solutions?

Why doesn't Java have such a simple thing?

Answer 1

Why not use the boolean primitive ?

e.g.

private boolean myFlag = false;

public void setMyFlag(boolean flag) {
   myFlag = flag;
}

Note your getter method can return a Boolean if required, due to the magic of autoboxing. This allows easy interchangeability between using primitives and their object equivalents (e.g. boolean vs. Boolean, or int vs. Integer).

So to address your edited responses re. the methods you have available,

public Object getAttribute(String attributeName)

can be implemented by returning an autoboxed boolean,.

Answer 2

Why don't you use the type boolean then? More info

Answer 3

What about just using the boolean primitive?

private boolean value;

public void setValue(boolean value) {
    this.value = value;
}

public boolean getValue() {
    return value;
}

Answer 4

Maybe write yourself a wrapper class

class BooleanHolder {
    public boolean value;
}

Or make a generic holder class (which means you will have to use class Boolean instead of primitive boolean):

class Holder<T> {
    public T value;
}

You then return the wrapper class instead of the value itself, which allows the value inside the wrapper to be modified.

Answer 5

Immutable classes are easier to work with. They'll never change and there will be no problems with concurrent code. (Basicly, there are fewer possiblities to break them.)

If you would like to return a reference to your Boolean value, you can use java.util.concurrent.atomic.AtomicBoolean if you're working with multible threads or plain old org.apache.commons.lang.mutable.MutableBoolean.

Answer 6

If I understand you correctly, you want to do something like this:

private boolean[] myBool = new boolean[1];
{ myBool[0] = false; }

  public Object getAttribute(String attributeName) {
    if (attributeName.equals("myBoolean")
      return myBool;
  }

and then elsewhere:

 boolean[] bool = (boolean[]) getAttribute("myBoolean");
 bool[0] = true;

This seems too tricky to me: I would be confused by this code. Booleans should be immutable and objects should not the updating the internal state of other objects directly.

If you absolutely must have this behavior, keep no local references: every time you need the value use the getAttribute method, then if the value has changed you will always be using the current value. Use some kind of a setter method to set the value, like Tom recommended.

Answer 7

Apache Commons Lang has a MutableBoolean class.

Answer 8

Are you really saying that you want callers to be able to modify the object's boolean value by manipulating what gets returned? So that the object and caller would share a reference to it?

Just so I understand, given:

class OddClass {
   private Boolean strangeFlag;
   public Object getAttrbiute(String attributeName) { 
      if (attributeName.equals("strangeflag")) return (Object)strangeFlag; 
      ...
   }
}

And then caller does:

   Boolean manipulableFlag = (Boolean) myOddClass.getAttrbiute ("strangeflag");

And then later, if caller changes the value of manipulableFlag, you want that change to happen in the OddClass instance, just as though caller had instead used a setAttrbiute method.

Is that what you're asking?

In that case, you'd need a holder class, as suggested by Adam.

Answer 9

If you are using Java 5 or higher then use AtomicBoolean