Source Code Cross Referenced for LookupTable.java in  » Web-Server » Jigsaw » org » w3c » util » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Web Server » Jigsaw » org.w3c.util 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        // LookupTable.java
002:        // $Id: LookupTable.java,v 1.3 2000/08/16 21:37:58 ylafon Exp $
003:        // (c) COPYRIGHT MIT, INRIA and Keio, 1999.
004:        // Please first read the full copyright statement in file COPYRIGHT.html
005:        package org.w3c.util;
006:
007:        import java.io.Serializable;
008:
009:        import java.util.Enumeration;
010:
011:        /**
012:         * A kind of hashtable (maps keys to values), useful for a limited number
013:         * of elements.
014:         * @version $Revision: 1.3 $
015:         * @author  Benoît Mahé (bmahe@w3.org)
016:         */
017:        public class LookupTable implements  Cloneable, Serializable {
018:
019:            /**
020:             * The default capacity.
021:             */
022:            public static final int DEFAULT_CAPACITY = 10;
023:
024:            private Object elements[] = null;
025:
026:            private Object keys[] = null;
027:
028:            private int count = 0;
029:
030:            private int capacity = 0;
031:
032:            /**
033:             * Returns the number of keys in this lookuptable.
034:             *
035:             * @return  the number of keys in this lookuptable.
036:             */
037:            public int size() {
038:                return count;
039:            }
040:
041:            /**
042:             * Tests if this lookuptable maps no keys to values.
043:             * @return  <code>true</code> if this lookuptable maps no keys to values;
044:             *          <code>false</code> otherwise.
045:             */
046:            public boolean isEmpty() {
047:                return count == 0;
048:            }
049:
050:            /**
051:             * Returns an enumeration of the keys in this lookuptable.
052:             *
053:             * @return  an enumeration of the keys in this lookuptable.
054:             * @see     java.util.Enumeration
055:             * @see     #elements()
056:             */
057:            public synchronized Enumeration keys() {
058:                return new ArrayEnumeration(keys, count);
059:            }
060:
061:            /**
062:             * Returns an enumeration of the values in this lookuptable.
063:             * Use the Enumeration methods on the returned object to fetch the elements
064:             * sequentially.
065:             *
066:             * @return  an enumeration of the values in this lookuptable.
067:             * @see     java.util.Enumeration
068:             * @see     #keys()
069:             */
070:            public synchronized Enumeration elements() {
071:                return new ArrayEnumeration(elements, count);
072:            }
073:
074:            /**
075:             * Tests if some key maps into the specified value in this lookuptable.
076:             * @param      value   a value to search for.
077:             * @return     <code>true</code> if and only if some key maps to the
078:             *             <code>value</code> argument in this lookuptable as 
079:             *             determined by the <tt>equals</tt> method;
080:             *             <code>false</code> otherwise.
081:             * @exception  NullPointerException  if the value is <code>null</code>.
082:             * @see        #containsKey(Object)
083:             */
084:            public synchronized boolean contains(Object value) {
085:                return (contains(elements, count, value) != -1);
086:            }
087:
088:            /**
089:             * Tests if the specified object is a key in this lookuptable.
090:             * @param   key   possible key.
091:             * @return  <code>true</code> if and only if the specified object 
092:             *          is a key in this lookuptable, as determined by the 
093:             *          <tt>equals</tt> method; <code>false</code> otherwise.
094:             * @see     #contains(Object)
095:             */
096:            public synchronized boolean containsKey(Object key) {
097:                return (contains(keys, count, key) != -1);
098:            }
099:
100:            private int contains(Object array[], int size, Object value) {
101:                if (value == null) {
102:                    throw new NullPointerException();
103:                }
104:                for (int i = 0; i < size; i++) {
105:                    if (array[i].equals(value))
106:                        return i;
107:                }
108:                return -1;
109:            }
110:
111:            /**
112:             * Returns the value to which the specified key is mapped in this 
113:             * lookuptable.
114:             * @param   key   a key in the lookuptable.
115:             * @return  the value to which the key is mapped in this lookuptable;
116:             *          <code>null</code> if the key is not mapped to any value in
117:             *          this lookuptable.
118:             * @see     #put(Object, Object)
119:             */
120:            public synchronized Object get(Object key) {
121:                int idx = contains(keys, count, key);
122:                if (idx != -1)
123:                    return elements[idx];
124:                return null;
125:            }
126:
127:            /**
128:             * Maps the specified <code>key</code> to the specified 
129:             * <code>value</code> in this lookuptable. Neither the key nor the 
130:             * value can be <code>null</code>. <p>
131:             *
132:             * The value can be retrieved by calling the <code>get</code> method 
133:             * with a key that is equal to the original key. 
134:             *
135:             * @param      key     the lookuptable key.
136:             * @param      value   the value.
137:             * @return     the previous value of the specified key in this lookuptable,
138:             *             or <code>null</code> if it did not have one.
139:             * @exception  NullPointerException  if the key or value is
140:             *               <code>null</code>.
141:             * @see     Object#equals(Object)
142:             * @see     #get(Object)
143:             */
144:            public synchronized Object put(Object key, Object value) {
145:                if (value == null) {
146:                    throw new NullPointerException();
147:                }
148:                int idx = contains(keys, count, key);
149:                if (idx == -1) {
150:                    if (count >= capacity) {
151:                        grow();
152:                    }
153:                    keys[count] = key;
154:                    elements[count] = value;
155:                    count++;
156:                    return null;
157:                } else {
158:                    Object previousValue = elements[idx];
159:                    elements[idx] = value;
160:                    return previousValue;
161:                }
162:            }
163:
164:            /**
165:             * Increases the capacity. This method is called automatically when the 
166:             * number of keys in the lookuptable exceeds this lookuptable's capacity.
167:             */
168:            protected void grow() {
169:                int newCapacity = capacity * 2 + 1;
170:                Object newElements[] = new Object[newCapacity];
171:                Object newKeys[] = new Object[newCapacity];
172:                System.arraycopy(elements, 0, newElements, 0, count);
173:                System.arraycopy(keys, 0, newKeys, 0, count);
174:                this .keys = newKeys;
175:                this .elements = newElements;
176:                this .capacity = newCapacity;
177:            }
178:
179:            /**
180:             * Removes the key (and its corresponding value) from this 
181:             * lookuptable. This method does nothing if the key is not in the 
182:             * lookuptable.
183:             *
184:             * @param   key   the key that needs to be removed.
185:             * @return  the value to which the key had been mapped in this lookuptable,
186:             *          or <code>null</code> if the key did not have a mapping.
187:             */
188:            public synchronized Object remove(Object key) {
189:                int idx = contains(keys, count, key);
190:                if (idx != -1) {
191:                    //remove this one by moving the last one here.
192:                    Object oldvalue = elements[idx];
193:                    count--;
194:                    keys[idx] = keys[count];
195:                    elements[idx] = elements[count];
196:                    keys[count] = null;
197:                    elements[count] = null;
198:                    return oldvalue;
199:                }
200:                return null;
201:            }
202:
203:            /**
204:             * Clears this lookuptable so that it contains no keys. 
205:             */
206:            public synchronized void clear() {
207:                this .count = 0;
208:                this .keys = new Object[capacity];
209:                this .elements = new Object[capacity];
210:            }
211:
212:            /**
213:             * Creates a shallow copy of this lookuptable. All the structure of the 
214:             * lookuptable itself is copied, but the keys and values are not cloned. 
215:             * This is a relatively expensive operation.
216:             *
217:             * @return  a clone of the lookuptable.
218:             */
219:            public synchronized Object clone() {
220:                try {
221:                    LookupTable l = (LookupTable) super .clone();
222:                    l.keys = new Object[capacity];
223:                    System.arraycopy(keys, 0, l.keys, 0, count);
224:                    l.elements = new Object[capacity];
225:                    System.arraycopy(elements, 0, l.elements, 0, count);
226:                    l.capacity = capacity;
227:                    l.count = count;
228:                    return l;
229:                } catch (CloneNotSupportedException e) {
230:                    // this shouldn't happen, since we are Cloneable
231:                    throw new InternalError();
232:                }
233:            }
234:
235:            /**
236:             * Returns a string representation of this <tt>Lookuptable</tt> object 
237:             * in the form of a set of entries, enclosed in braces and separated 
238:             * by the ASCII characters "<tt>,&nbsp;</tt>" (comma and space). Each 
239:             * entry is rendered as the key, an equals sign <tt>=</tt>, and the 
240:             * associated element, where the <tt>toString</tt> method is used to 
241:             * convert the key and element to strings. <p>Overrides to 
242:             * <tt>toString</tt> method of <tt>Object</tt>.
243:             *
244:             * @return  a string representation of this lookuptable.
245:             */
246:            public synchronized String toString() {
247:                StringBuffer buffer = new StringBuffer();
248:                for (int i = 0; i < count; i++) {
249:                    buffer.append("[" + keys[i] + "," + elements[i] + "]");
250:                }
251:                return buffer.toString();
252:            }
253:
254:            /**
255:             * Constructor.
256:             * @param capacity the initial capacity
257:             */
258:            public LookupTable(int capacity) {
259:                this .count = 0;
260:                this .capacity = capacity;
261:                this .elements = new Object[capacity];
262:                this .keys = new Object[capacity];
263:            }
264:
265:            /**
266:             * Constructor, build a LookupTable with a initial capacity set to
267:             * DEFAULT_CAPACITY.
268:             */
269:            public LookupTable() {
270:                this(DEFAULT_CAPACITY);
271:            }
272:
273:        }
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