Re: Using an enum in a constructor

 Daniel Pitts <>
Thu, 20 Sep 2007 21:59:56 -0000
On Sep 20, 2:34 pm, Wojtek <> wrote:

Daniel Pitts wrote :

On Sep 20, 1:33 pm, Wojtek <> wrote:

Given the following:
public class Foo
  private static final int DEFAULT_LENGTH = 30;
  private Type ivType;
  private int ivLength;

  public enum Type

  public Foo(Type type)

  public Foo(Type.VARIABLE varType, int length)

  private Foo(Type type, int length)
    ivType = type;
    ivLength = length;


The compiler complains that Type.VARIABLE cannot be used. Obviously
what I want is that if the Type is VARIABLE, then I want the length in
the constructor, otherwise I will use the default length.

And yes I know I can have a constructor that only takes (int length)
and then assume that the Type is VARIABLE. That is not the point here.

Wojtek :-)

Try using the Static Factory approach instead

public class Foo {
  enum Type {
    a, b, c

  private Foo(Type type, int length) {
      // ...

  public static Foo createVariable(int length) {
       return new Foo(Type.a, length);

  public static Foo createSomething(Type type) {
       return new Foo(type, DEFAULT_LENGTH;
  public sattic Foo createSomething(Type type, int length) {
       return new Foo(type, length);

This is the same as having a constructor which takes just (int length).
I still need to make an assumption that type is VARIABLE.

Wojtek :-)

Its not an assumption, its explicit by the name of the method

In general though, if you have a "Type" token, you might be going
about your solution the wrong way. Have you considered using a more
polymorphic approach?

abstract class Foo {

class VariableFoo extends Foo {

class OtherFoo extends Foo {


That way, the "Type" of foo, is actually the *type* of foo! (Go

Or, if the Type can change over time, use the State pattern (same
idea, just wrapper)

class Foo {
   FooType type;

   public Foo(FooType type) {}

abstract class FooType {

class FooVariable extends FooType {
   FooVariable(int length) {}

class FooOther extends FooType {

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