SmallMap.java

/*******************************************************************************
 * Copyright (c) 2002 - 2006 IBM Corporation.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package com.ibm.wala.util.collections;

import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

import com.ibm.wala.util.debug.Assertions;
import com.ibm.wala.util.debug.UnimplementedError;

/**
 * A simple implementation of Map; intended for Maps with few elements. Optimized for space, not time -- use with care.
 */
public class SmallMap<K, V> implements Map<K, V> {

  private static final boolean DEBUG_USAGE = false;

  private static final int DEBUG_MAX_SIZE = 20;

  // this Map contains keysAndValues.length / 2 entries.
  // in the following array, entries 0 ... keysAndValues.length/2 - 1 are keys.
  // entries keysAndValues.length/2 .. keysAndValues.length are values.
  private Object[] keysAndValues;

  /*
   */
  @Override
  public int size() {
    if (keysAndValues == null) {
      return 0;
    } else {
      return keysAndValues.length / 2;
    }
  }

  /**
   * Use with care.
   * 
   * @return the ith key
   */
  @SuppressWarnings("unchecked")
  public K getKey(int i) throws IllegalStateException {
    if (keysAndValues == null) {
      throw new IllegalStateException("getKey on empty map");
    }
    try {
      return (K) keysAndValues[i];
    } catch (ArrayIndexOutOfBoundsException e) {
      throw new IllegalArgumentException("invalid i: " + i);
    }
  }

  /**
   * Use with care.
   * 
   * @return the ith key
   */
  public Object getValue(int i) throws IllegalStateException {
    if (keysAndValues == null) {
      throw new IllegalStateException("getValue on empty map");
    }
    try {
      return keysAndValues[size() + i];
    } catch (ArrayIndexOutOfBoundsException e) {
      throw new IllegalArgumentException("illegal i: " + i);
    }
  }

  /*
   * @see java.util.Map#isEmpty()
   */
  @Override
  public boolean isEmpty() {
    return (keysAndValues == null);
  }

  /*
   * @see java.util.Map#containsKey(java.lang.Object)
   */
  @Override
  public boolean containsKey(Object key) {
    for (int i = 0; i < size(); i++) {
      if (keysAndValues[i].equals(key)) {
        return true;
      }
    }
    return false;
  }

  /*
   * @see java.util.Map#containsValue(java.lang.Object)
   */
  @Override
  public boolean containsValue(Object value) {
    if (keysAndValues == null) {
      return false;
    }
    for (int i = size(); i < keysAndValues.length; i++) {
      Object v = keysAndValues[i];
      if (v == null) {
        if (value == null) {
          return true;
        }
      } else {
        if (v.equals(value)) {
          return true;
        }
      }
    }
    return false;
  }

  /*
   * @see java.util.Map#get(java.lang.Object)
   */
  @Override
  @SuppressWarnings("unchecked")
  public V get(Object key) {

    if (key != null)
      for (int i = 0; i < size(); i++) {
        if (keysAndValues[i] != null && keysAndValues[i].equals(key)) {
          return (V) keysAndValues[size() + i];
        }
      }

    return null;
  }

  private void growByOne() {
    Object[] old = keysAndValues;
    int length = (old == null) ? 0 : old.length;
    keysAndValues = new Object[length + 2];
    for (int i = 0; i < length / 2; i++) {
      keysAndValues[i] = old[i];
    }
    for (int i = 0; i < length / 2; i++) {
      keysAndValues[i + 1 + length / 2] = old[length / 2 + i];
    }

  }

  /*
   * @see java.util.Map#put(java.lang.Object, java.lang.Object)
   */
  @Override
  @SuppressWarnings({ "unchecked", "unused" })
  public V put(Object key, Object value) {
    if (key == null) {
      throw new IllegalArgumentException("null key");
    }
    for (int i = 0; i < size(); i++) {
      if (keysAndValues[i] != null && keysAndValues[i].equals(key)) {
        V result = (V) keysAndValues[size() + i];
        keysAndValues[size() + i] = value;
        return result;
      }
    }
    if (DEBUG_USAGE && size() >= DEBUG_MAX_SIZE) {
      Assertions.UNREACHABLE("too many elements in a SmallMap");
    }
    growByOne();
    keysAndValues[size() - 1] = key;
    keysAndValues[keysAndValues.length - 1] = value;
    return null;
  }

  /*
   * @see java.util.Map#remove(java.lang.Object)
   */
  @Override
  public V remove(Object key) throws UnsupportedOperationException {
    throw new UnsupportedOperationException();
  }

  /*
   * @see java.util.Map#putAll(java.util.Map)
   */
  @Override
  public void putAll(Map<? extends K, ? extends V> t) throws UnsupportedOperationException {
    throw new UnsupportedOperationException();
  }

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

  /*
   * @see java.util.Map#keySet()
   */
  @Override
  @SuppressWarnings("unchecked")
  public Set<K> keySet() {
    // TODO: use a better set implementation, SOON!!
    HashSet<K> result = HashSetFactory.make(size());
    for (int i = 0; i < size(); i++) {
      result.add((K) keysAndValues[i]);
    }
    return result;
  }

  /*
   * @see java.util.Map#values()
   */
  @Override
  @SuppressWarnings("unchecked")
  public Collection<V> values() {
    int s = size();
    if (s == 0) {
      return Collections.emptySet();
    }
    HashSet<V> result = HashSetFactory.make(s);
    for (int i = s; i < keysAndValues.length; i++) {
      result.add((V) keysAndValues[i]);
    }
    return result;
  }

  /**
   * @throws UnimplementedError 
   */
  @Override
  public Set<Map.Entry<K, V>> entrySet() throws UnimplementedError {
    Assertions.UNREACHABLE("must implement entrySet");
    return null;
  }

}