Number for each enum item?

Question

Is it possible to define something like this in java?

C# code:

public enum Character
{
    A = 1,

    B = 2,

    C = 4,

    D = 8

}


...

Character ch = /* from user */

if(ch & Character.A)
{
    // some operation...
}

for example if ch set to Character.B then result of if will be false:

ch = 00000000 00000000 00000000 00000010
A  = 00000000 00000000 00000000 00000001
------------------------------------------
&    00000000 00000000 00000000 00000000

I want to implement something like that! Is it ever possible in Java?

Answer 1

Well, you can nearly do that:

public enum CharEnum // Let's avoid java.lang.* clashes
{
    A(1), B(2), C(4), D(8);

    private final int mask;

    private CharEnum(int mask)
    {
        this.mask = mask;
    }

    public int getMask()
    {
        return mask;
    }
}

Then:

CharEnum ch = /* from user */

if ((ch.getMask() & CharEnum.A.getMask()) > 0)
{
    // some operation...
}

This can be useful in some situations, but as Michael said you should definitely look at EnumSet for general "set of values" options.

If you do decide to go for an enum with values, you can put extra logic within the enum itself:

public enum CharEnum
{
    // Other code as before

    public boolean overlapsWith(CharEnum ch)
    {
        return (ch.mask & mask) > 0;
    }
}

Answer 2

(Of course, choosing Character as the name of your enum is very confusing as it creates a conflict with java.lang.Character which is automatically imported into every compilation unit)

You can use the ordinal() method to get the integer associated with an enum constant. Anyway, I got a feeling that what you are trying to achieve may be realized by enum-defined methods. I mean, Java's enum are more powerful than C/C++'s because you can associate behavior with them.

  public enum Chr {
    A {
       @Override public void doSomething(int c) {
         // some operation ...
       }
    },
    B,
    C,
    D;

    public void doSomething(int c) { 
      // some default behavior
    }
  }

Following your comment:

You can define a field which will hold this value, and have the constructor initialize it, as follows:

  public enum Chr {
    A(1),
    B(2),
    C(4),
    D(8)
    ;

    public Chr(int n) { value = n; }        
    public final int value;
  }



  Character ch = ... // from user
  if(ch & Chr.A.value) {
     ...
  }