DefaultMapAdapter.java

package tc.oc.commons.core.util;

import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

/**
 * Adapt a Map to return a default value for missing keys.
 * The default value can be constant or generated dynamically
 * by a DefaultProvider. Only the get() method uses default
 * values. All other methods behave normally for missing keys.
 */

public class DefaultMapAdapter<K, V> implements Map<K, V> {

    private final Map<K, V> map;
    private final DefaultProvider<? super K, ? extends V> defaultProvider;
    private final boolean putDefault;

    public DefaultMapAdapter(Map<K, V> map, DefaultProvider<? super K, ? extends V> defaultProvider, boolean putDefault) {
        this.defaultProvider = defaultProvider;
        this.map = map;
        this.putDefault = putDefault;
    }

    public DefaultMapAdapter(Map<K, V> map, final V defaultValue, boolean putDefault) {
        this(map, new DefaultProvider<K, V>() {
            @Override
            public V get(Object key) {
                return defaultValue;
            }
        }, putDefault);
    }

    public DefaultMapAdapter(final V defaultValue, boolean putDefault) {
        this(new HashMap<K, V>(), defaultValue, putDefault);
    }

    public DefaultMapAdapter(DefaultProvider<? super K, ? extends V> defaultProvider, boolean putDefault) {
        this(new HashMap<K, V>(), defaultProvider, putDefault);
    }

    public DefaultMapAdapter(Map<K, V> map, final V defaultValue) {
        this(map, defaultValue, false);
    }

    public DefaultMapAdapter(Map<K, V> map, DefaultProvider<? super K, ? extends V> defaultProvider) {
        this(map, defaultProvider, false);
    }

    public DefaultMapAdapter(final V defaultValue) {
        this(defaultValue, false);
    }

    public DefaultMapAdapter(DefaultProvider<? super K, ? extends V> defaultProvider) {
        this(defaultProvider, false);
    }

    @Override
    public V get(Object key) {
        V value = this.map.get(key);
        if(value == null) {
            value = this.defaultProvider.get((K) key);
            if(this.putDefault) this.map.put((K) key, value);
        }
        return value;
    }

    public V getOrDefault(K key) {
        V value = this.map.get(key);
        if(value == null) {
            value = this.defaultProvider.get(key);
        }
        return value;
    }

    public V getOrCreate(K key) {
        V value = this.map.get(key);
        if(value == null) {
            value = this.defaultProvider.get(key);
            this.map.put(key, value);
        }
        return value;
    }

    public V getOrNull(K key) {
        return this.map.get(key);
    }

    @Override
    public void clear() {
        map.clear();
    }

    @Override
    public boolean containsKey(Object key) {
        return map.containsKey(key);
    }

    @Override
    public boolean containsValue(Object value) {
        return map.containsValue(value);
    }

    @Override
    public Set<Entry<K,V>> entrySet() {
        return map.entrySet();
    }

    @Override
    public boolean equals(Object o) {
        return map.equals(o);
    }

    @Override
    public int hashCode() {
        return map.hashCode();
    }

    @Override
    public boolean isEmpty() {
        return map.isEmpty();
    }

    @Override
    public Set<K> keySet() {
        return map.keySet();
    }

    /**
     * If the given key was not previously in the map, the default value is returned, rather than null.
     * This is so that put(x, ...) always returns the same thing as get(x) for any given state.
     *
     * {@link #putNoDefault} can be used if you want null returned for new keys, instead of the default.
     */
    public V put(K key, V value) {
        V previous = map.put(key, value);
        return previous != null ? previous : this.defaultProvider.get(key);
    }

    public V putNoDefault(K key, V value) {
        return map.put(key, value);
    }

    public void putAll(Map<? extends K, ? extends V> m) {
        map.putAll(m);
    }

    @Override
    public V remove(Object key) {
        return map.remove(key);
    }

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

    @Override
    public Collection<V> values() {
        return map.values();
    }
}