MicroMap.java Source code

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Here is the source code for MicroMap.java

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/*
 * 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.
 */

import java.io.Serializable;
import java.util.AbstractList;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;

/**
 * An implementation of the java.util.Map interface which can only hold a single object. This is
 * particularly useful to control memory usage in Wicket because many containers hold only a single
 * component.
 * 
 * @author Jonathan Locke
 * @param <K>
 *            Key type
 * @param <V>
 *            Value type
 */
public final class MicroMap<K, V> implements Map<K, V>, Serializable {
    private static final long serialVersionUID = 1L;

    /** The maximum number of entries this map supports. */
    public static final int MAX_ENTRIES = 1;

    /** The one and only key in this tiny map */
    private K key;

    /** The value for the only key in this tiny map */
    private V value;

    /**
     * Constructor
     */
    public MicroMap() {
    }

    /**
     * Constructs map with a single key and value pair.
     * 
     * @param key
     *            The key
     * @param value
     *            The value
     */
    public MicroMap(final K key, final V value) {
        put(key, value);
    }

    /**
     * @return True if this MicroMap is full
     */
    public boolean isFull() {
        return size() == MAX_ENTRIES;
    }

    /**
     * @see java.util.Map#size()
     */
    public int size() {
        return (key != null) ? 1 : 0;
    }

    /**
     * @see java.util.Map#isEmpty()
     */
    public boolean isEmpty() {
        return size() == 0;
    }

    /**
     * @see java.util.Map#containsKey(java.lang.Object)
     */
    public boolean containsKey(final Object key) {
        return key.equals(this.key);
    }

    /**
     * @see java.util.Map#containsValue(java.lang.Object)
     */
    public boolean containsValue(final Object value) {
        return value.equals(this.value);
    }

    /**
     * @see java.util.Map#get(java.lang.Object)
     */
    public V get(final Object key) {
        if (key.equals(this.key)) {
            return value;
        }

        return null;
    }

    /**
     * @see java.util.Map#put(java.lang.Object, java.lang.Object)
     */
    public V put(final K key, final V value) {
        // Replace?
        if (key.equals(this.key)) {
            final V oldValue = this.value;

            this.value = value;

            return oldValue;
        } else {
            // Is there room for a new entry?
            if (size() < MAX_ENTRIES) {
                // Store
                this.key = key;
                this.value = value;

                return null;
            } else {
                throw new IllegalStateException("Map full");
            }
        }
    }

    /**
     * @see java.util.Map#remove(java.lang.Object)
     */
    public V remove(final Object key) {
        if (key.equals(this.key)) {
            final V oldValue = value;

            this.key = null;
            value = null;

            return oldValue;
        }

        return null;
    }

    /**
     * @see java.util.Map#putAll(java.util.Map)
     */
    public void putAll(final Map<? extends K, ? extends V> map) {
        if (map.size() <= MAX_ENTRIES) {
            final Entry<? extends K, ? extends V> e = map.entrySet().iterator().next();

            put(e.getKey(), e.getValue());
        } else {
            throw new IllegalStateException("Map full.  Cannot add " + map.size() + " entries");
        }
    }

    /**
     * @see java.util.Map#clear()
     */
    public void clear() {
        key = null;
        value = null;
    }

    /**
     * @see java.util.Map#keySet()
     */
    public Set<K> keySet() {
        return new AbstractSet<K>() {
            @Override
            public Iterator<K> iterator() {
                return new Iterator<K>() {
                    public boolean hasNext() {
                        return index < MicroMap.this.size();
                    }

                    public K next() {
                        if (!hasNext()) {
                            throw new NoSuchElementException();
                        }
                        index++;

                        return key;
                    }

                    public void remove() {
                        MicroMap.this.clear();
                    }

                    int index;
                };
            }

            @Override
            public int size() {
                return MicroMap.this.size();
            }
        };
    }

    /**
     * @see java.util.Map#values()
     */
    public Collection<V> values() {
        return new AbstractList<V>() {
            @Override
            public V get(final int index) {
                if (index > size() - 1) {
                    throw new IndexOutOfBoundsException();
                }
                return value;
            }

            @Override
            public int size() {
                return MicroMap.this.size();
            }
        };
    }

    /**
     * @see java.util.Map#entrySet()
     */
    public Set<Entry<K, V>> entrySet() {
        return new AbstractSet<Entry<K, V>>() {
            @Override
            public Iterator<Entry<K, V>> iterator() {
                return new Iterator<Entry<K, V>>() {
                    public boolean hasNext() {
                        return index < MicroMap.this.size();
                    }

                    public Entry<K, V> next() {
                        if (!hasNext()) {
                            throw new NoSuchElementException();
                        }
                        index++;

                        return new Map.Entry<K, V>() {
                            public K getKey() {
                                return key;
                            }

                            public V getValue() {
                                return value;
                            }

                            public V setValue(final V value) {
                                final V oldValue = MicroMap.this.value;

                                MicroMap.this.value = value;

                                return oldValue;
                            }
                        };
                    }

                    public void remove() {
                        clear();
                    }

                    int index = 0;
                };
            }

            @Override
            public int size() {
                return MicroMap.this.size();
            }
        };
    }
}