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Commons Collections example source code file (EntrySetMapIterator.java)

This example Commons Collections source code file (EntrySetMapIterator.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Commons Collections tags/keywords

entrysetmapiterator, illegalstateexception, illegalstateexception, iterator, iterator, map, mapiterator, mapiterator, object, object, resettableiterator, string, util

The Commons Collections EntrySetMapIterator.java source code

/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  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,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package org.apache.commons.collections.iterators;

import java.util.Iterator;
import java.util.Map;

import org.apache.commons.collections.MapIterator;
import org.apache.commons.collections.ResettableIterator;

/**
 * Implements a <code>MapIterator using a Map entrySet.
 * Reverse iteration is not supported.
 * <pre>
 * MapIterator it = map.mapIterator();
 * while (it.hasNext()) {
 *   Object key = it.next();
 *   Object value = it.getValue();
 *   it.setValue(newValue);
 * }
 * </pre>
 *  
 * @since Commons Collections 3.0
 * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
 *
 * @author Stephen Colebourne
 */
public class EntrySetMapIterator implements MapIterator, ResettableIterator {
    
    private final Map map;
    private Iterator iterator;
    private Map.Entry last;
    private boolean canRemove = false;
    
    /**
     * Constructor.
     * 
     * @param map  the map to iterate over
     */
    public EntrySetMapIterator(Map map) {
        super();
        this.map = map;
        this.iterator = map.entrySet().iterator();
    }

    //-----------------------------------------------------------------------    
    /**
     * Checks to see if there are more entries still to be iterated.
     *
     * @return <code>true if the iterator has more elements
     */
    public boolean hasNext() {
        return iterator.hasNext();
    }

    /**
     * Gets the next <em>key from the Map.
     *
     * @return the next key in the iteration
     * @throws java.util.NoSuchElementException if the iteration is finished
     */
    public Object next() {
        last = (Map.Entry) iterator.next();
        canRemove = true;
        return last.getKey();
    }

    //-----------------------------------------------------------------------
    /**
     * Removes the last returned key from the underlying <code>Map.
     * <p>
     * This method can be called once per call to <code>next().
     *
     * @throws UnsupportedOperationException if remove is not supported by the map
     * @throws IllegalStateException if <code>next() has not yet been called
     * @throws IllegalStateException if <code>remove() has already been called
     *  since the last call to <code>next()
     */
    public void remove() {
        if (canRemove == false) {
            throw new IllegalStateException("Iterator remove() can only be called once after next()");
        }
        iterator.remove();
        last = null;
        canRemove = false;
    }
    
    //-----------------------------------------------------------------------
    /**
     * Gets the current key, which is the key returned by the last call
     * to <code>next().
     *
     * @return the current key
     * @throws IllegalStateException if <code>next() has not yet been called
     */
    public Object getKey() {
        if (last == null) {
            throw new IllegalStateException("Iterator getKey() can only be called after next() and before remove()");
        }
        return last.getKey();
    }

    /**
     * Gets the current value, which is the value associated with the last key
     * returned by <code>next().
     *
     * @return the current value
     * @throws IllegalStateException if <code>next() has not yet been called
     */
    public Object getValue() {
        if (last == null) {
            throw new IllegalStateException("Iterator getValue() can only be called after next() and before remove()");
        }
        return last.getValue();
    }

    /**
     * Sets the value associated with the current key.
     *
     * @param value  the new value
     * @return the previous value
     * @throws UnsupportedOperationException if setValue is not supported by the map
     * @throws IllegalStateException if <code>next() has not yet been called
     * @throws IllegalStateException if <code>remove() has been called since the
     *  last call to <code>next()
     */
    public Object setValue(Object value) {
        if (last == null) {
            throw new IllegalStateException("Iterator setValue() can only be called after next() and before remove()");
        }
        return last.setValue(value);
    }

    //-----------------------------------------------------------------------
    /**
     * Resets the state of the iterator.
     */
    public void reset() {
        iterator = map.entrySet().iterator();
        last = null;
        canRemove = false;
    }
    
    /**
     * Gets the iterator as a String.
     * 
     * @return a string version of the iterator
     */    
    public String toString() {
        if (last != null) {
            return "MapIterator[" + getKey() + "=" + getValue() + "]";
        } else {
            return "MapIterator[]";
        }
    }
    
}

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