Java Tutorial/Collections/LinkedHashMap

A Least Recently Used Cache

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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.util.LinkedHashMap;
import java.util.Map;
/**
 * A Least Recently Used Cache
 *
 * @version $Revision: 747062 $
 */
public class LRUCache<K, V> extends LinkedHashMap<K, V> {
    private static final long serialVersionUID = -342098639681884413L;
    private int maxCacheSize = 10000;
    public LRUCache(int maximumCacheSize) {
        this(maximumCacheSize, maximumCacheSize, 0.75f, true);
    }
    /**
     * Constructs an empty <tt>LRUCache</tt> instance with the
     * specified initial capacity, maximumCacheSize,load factor and ordering mode.
     *
     * @param initialCapacity  the initial capacity.
     * @param maximumCacheSize the max capacity.
     * @param loadFactor       the load factor.
     * @param accessOrder      the ordering mode - <tt>true</tt> for
     *                         access-order, <tt>false</tt> for insertion-order.
     * @throws IllegalArgumentException if the initial capacity is negative
     *                                  or the load factor is non positive.
     */
    public LRUCache(int initialCapacity, int maximumCacheSize, float loadFactor, boolean accessOrder) {
        super(initialCapacity, loadFactor, accessOrder);
        this.maxCacheSize = maximumCacheSize;
    }
    /**
     * Returns the maxCacheSize.
     */
    public int getMaxCacheSize() {
        return maxCacheSize;
    }
    protected boolean removeEldestEntry(Map.Entry entry) {
        return size() > maxCacheSize;
    }
}

Check if a particular element exists in Java LinkedHashSet

import java.util.LinkedHashSet;
public class Main {
  public static void main(String[] args) {
    LinkedHashSet<Integer> lhashSet = new LinkedHashSet<Integer>();
    lhashSet.add(new Integer("1"));
    lhashSet.add(new Integer("2"));
    lhashSet.add(new Integer("3"));
    System.out.println(lhashSet.contains(new Integer("3")));
  }
}

Check if a particular key exists in Java LinkedHashMap example

import java.util.LinkedHashMap;
public class Main {
  public static void main(String[] args) {
    LinkedHashMap<String,String> lHashMap = new LinkedHashMap<String,String>();
    lHashMap.put("1", "One");
    lHashMap.put("2", "Two");
    lHashMap.put("3", "Three");
    boolean blnExists = lHashMap.containsKey("3");
    System.out.println(blnExists);
  }
}

Check if a particular value exists in Java LinkedHashMap example

import java.util.LinkedHashMap;
public class Main {
  public static void main(String[] args) {
    LinkedHashMap<String,String> lHashMap = new LinkedHashMap<String,String>();
    lHashMap.put("1", "One");
    lHashMap.put("2", "Two");
    lHashMap.put("3", "Three");
    boolean blnExists = lHashMap.containsValue("Two");
    System.out.println(blnExists);
  }
}

Copy all elements of Java LinkedHashSet to an Object Array

import java.util.LinkedHashSet;
public class Main {
  public static void main(String[] args) {
    LinkedHashSet<Integer> lhashSet = new LinkedHashSet<Integer>();
    lhashSet.add(new Integer("1"));
    lhashSet.add(new Integer("2"));
    lhashSet.add(new Integer("3"));
    Object[] objArray = lhashSet.toArray();
    for (Object inte: objArray){
      System.out.println(inte);
    }
  }
}

Get Set view of Keys from Java LinkedHashMap

import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Set;
public class Main {
  public static void main(String[] args) {
    LinkedHashMap<String,String> lHashMap = new LinkedHashMap<String,String>();
    lHashMap.put("1", "One");
    lHashMap.put("2", "Two");
    lHashMap.put("3", "Three");
    Set st = lHashMap.keySet();
    Iterator itr = st.iterator();
    while (itr.hasNext()){
      System.out.println(itr.next());
    }
    st.remove("2");
    boolean blnExists = lHashMap.containsKey("2");
    System.out.println(blnExists);
  }
}
/*
1
2
3
false
*/

Get Size of Java LinkedHashMap

import java.util.LinkedHashMap;
public class Main {
  public static void main(String[] args) {
    LinkedHashMap<String,String> lHashMap = new LinkedHashMap<String,String>();
    System.out.println(lHashMap.size());
    lHashMap.put("1", "One");
    lHashMap.put("2", "Two");
    lHashMap.put("3", "Three");
    System.out.println(lHashMap.size());
    Object obj = lHashMap.remove("2");
    System.out.println(lHashMap.size());
  }
}

Iterate through the values of Java LinkedHashMap

import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedHashMap;
public class Main {
  public static void main(String[] args) {
    LinkedHashMap<String,String> lHashMap = new LinkedHashMap<String,String>();
    lHashMap.put("1", "One");
    lHashMap.put("2", "Two");
    lHashMap.put("3", "Three");
    Collection c = lHashMap.values();
    Iterator itr = c.iterator();
    while (itr.hasNext()){
      System.out.println(itr.next());
    }
  }
}

Remove all values from Java LinkedHashMap

import java.util.LinkedHashMap;
public class Main {
  public static void main(String[] args) {
    LinkedHashMap<String,String> lHashMap = new LinkedHashMap<String,String>();
    lHashMap.put("1", "One");
    lHashMap.put("2", "Two");
    lHashMap.put("3", "Three");
    lHashMap.clear();
    System.out.println(lHashMap.size());
  }
}

Remove value from Java LinkedHashMap

import java.util.LinkedHashMap;
public class Main {
  public static void main(String[] args) {
    LinkedHashMap<String,String> lHashMap = new LinkedHashMap<String,String>();
    lHashMap.put("1", "One");
    lHashMap.put("2", "Two");
    lHashMap.put("3", "Three");
    Object obj = lHashMap.remove("2");
    System.out.println(obj + " was Removed");
  }
}

What you can do with a LinkedHashMap.

import java.util.LinkedHashMap;
public class MainClass {
  public static void main(String[] args) {
    LinkedHashMap linkedMap = new LinkedHashMap();
    for (int i = 0; i < 10; i++) {
      linkedMap.put(i, i);
    }
    System.out.println(linkedMap);
    // Least-recently used order:
    linkedMap = new LinkedHashMap(16, 0.75f, true);
    for (int i = 0; i < 10; i++) {
      linkedMap.put(i, i);
    }
    System.out.println(linkedMap);
    for (int i = 0; i < 7; i++)
      // Cause accesses:
      System.out.println(linkedMap.get(i));
    System.out.println(linkedMap);
  }
}

{0=0, 1=1, 2=2, 3=3, 4=4, 5=5, 6=6, 7=7, 8=8, 9=9}
{0=0, 1=1, 2=2, 3=3, 4=4, 5=5, 6=6, 7=7, 8=8, 9=9}
0
1
2
3
4
5
6
{7=7, 8=8, 9=9, 0=0, 1=1, 2=2, 3=3, 4=4, 5=5, 6=6}