org.apache.cocoon.util.EnumerationFactory Maven / Gradle / Ivy
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* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
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* See the License for the specific language governing permissions and
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//----------------------------------------------------------------------
// This software is provided as is in the hope that it might be found
// useful.
// You may use and modify it freely provided you keep this copyright
// notice unchanged and mark modifications appropriately.
//
// Bug reports and proposals for improvements are welcome. Please send
// them to the eMail address below.
//
// Christoph Karl Walter Grein
// Hauptstr. 42
// D-86926 Greifenberg
// Germany
//
// eMail: [email protected]
//
// Copyright (c) 1998 Christoph Karl Walter Grein
//----------------------------------------------------------------------
//====================================================================
// Author Christoph Grein
// Version 1.1
// Date 7 February 1998
//====================================================================
// A factory for the creation of enumeration types (missing in Java).
// The same operations are provided as for Ada, only representation
// specification is missing (which does not seem to make much sense
// in Java).
//
// The idea behind this implementation model is the following:
//
// Each enumeration object [or literal as called in Ada] is internally
// represented by its position number [like in Ada] starting with 0
// for the first one. For external representation, an image string
// may also be defined.
// All operations on enumerations (order relations between objects,
// iterators [in the Ada sense for getting the successor and predeces-
// sor of an object]) are implemented on the internal position number.
//
// Implementing the Ada 'Pos attribute as a function getPos () is
// straight forward as is the implementation of 'Image as a function
// toString () [*], whereas their reverse operations 'Val and 'Value
// present a bit of a problem.
// In order to be able to access all objects created for the given
// class, we define a vector and let the constructors add each object
// upon creation to this vector. Thus each object's position number
// is also its vector index. So getVal [Ada's 'Val] simply returns
// the object stored at the given place; getObject [Ada's 'Value]
// loops thru the vector until it finds the object with the given
// string.
//
// [*] The name toString has deliberately been chosen because of
// Java's convention of calling an operation with this name whenever
// an object's name appears in string context.
//
// There is one last point to take care of. An enumeration class has
// only a fixed number of objects, so we must inhibit the creation of
// new objects (with the "new" operator) outside of the enumeration
// class. However, in order to make this EnumerationFactory class
// work, the constructors need to be public. Therefore we set up the
// requirement that upon derivation from class EnumerationFactory all
// objects be created in the derivation class (using all capital
// letters according to Java's convention) and the constructors be
// made private.
//
// For this class at work, see the example classes EnumerationExample
// and Test_EnumerationExample, which present a few objects and opera-
// tions on them.
//
// Comments and improvements are welcome, see e-mail address above.
//====================================================================
// History:
// Author Version Date Reason for Change
// C.G. 1.0 03.02.1998
// C.G. 1.1 07.02.1998 getObject returns null if nothing found
//====================================================================
package org.apache.cocoon.util;
import java.util.Vector;
/**
* A factory for the creation of enumeration types (missing in Java).
* The same operations are provided as for Ada, only representation
* specification is missing (which does not seem to make much sense
* in Java).
* Enumeration classes are to be derived from this class thereby
* making the constructors private to inhibit creation outside of
* the derived class.
*
* @version $Id: EnumerationFactory.java 490773 2006-12-28 19:27:50Z danielf $
*/
public class EnumerationFactory {
private static Vector allObjects = // must be here JDK 1.1.3
new Vector (0, 1); // empty, increment by 1
private int pos;
private String image;
/**
* Constructors with and without a string representation (image).
* Make constructors private upon derivation.
* Be careful: No check is made that the image string is unique!
* @param image
*/
public EnumerationFactory(String image) {
this.pos = allObjects.size();
this.image = image;
allObjects.addElement(this);
}
public EnumerationFactory() {
this ("");
}
//--------------------------------------------------------------------------
// Order relations:
/**
* Order relations Object.op (OtherObject) representing the relation
* Object op OtherObject.
* @param e the right operand
*/
public boolean lt(EnumerationFactory e) { // "<"
return this.getPos() < e.getPos();
}
public boolean le(EnumerationFactory e) { // "<="
return this.getPos() <= e.getPos();
}
public boolean gt(EnumerationFactory e) { // ">"
return this.getPos() > e.getPos();
}
public boolean ge(EnumerationFactory e) { // ">="
return this.getPos() >= e.getPos ();
}
// "==" and "equals" are inherited.
//--------------------------------------------------------------------------
// Numeric representation:
public int getPos() { // Ada'Pos
return pos;
}
/**
* Access to the numeric representation.
* @param value the numeric value
*/
public static EnumerationFactory getVal(int value) { // Ada'Val
return (EnumerationFactory)allObjects.elementAt(value);
}
//--------------------------------------------------------------------------
// Iterator:
public static EnumerationFactory getFirst() { // Ada'First
return getVal(0);
}
public static EnumerationFactory getLast() { // Ada'Last
return getVal(allObjects.size() - 1);
}
public EnumerationFactory getNext () { // Ada'Succ
return getVal(this.getPos() + 1);
}
public EnumerationFactory getPrev () { // Ada'Pred
return getVal(this.getPos() - 1);
}
//--------------------------------------------------------------------------
// String representation:
public String toString() { // Ada'Image
return image;
}
public static EnumerationFactory getObject(String image) { // Ada'Value
EnumerationFactory found;
// Linear search seems good enough because there presumably
// will not be too many literals.
for (int i = 0 ; i < allObjects.size() ; i++) {
found = (EnumerationFactory) allObjects.elementAt(i);
if (found.toString().equals(image)) {
return found;
}
}
return null;
}
}