linkedhashmap中關於LRU算法的實現

//LinkedHashMap的一個構造函數，當參數accessOrder為true時，即會按照訪問順序排序，最近訪問的放在最前，最早訪問的放在后面
public LinkedHashMap(int initialCapacity, float loadFactor, boolean accessOrder) {
        super(initialCapacity, loadFactor);
        this.accessOrder = accessOrder;
}

LRU是Least Recently Used 的縮寫，翻譯過來就是“最近最少使用”，LRU緩存就是使用這種原理實現，簡單的說就是緩存一定量的數據，當超過設定的閾值時就把一些過期的數據刪除掉，比如我們緩存10000條數據，當數據小於10000時可以隨意添加，當超過10000時就需要把新的數據添加進來，同時要把過期數據刪除，以確保我們最大緩存10000條，那怎么確定刪除哪條過期數據呢，采用LRU算法實現的話就是將最老的數據刪掉，Java版的LRU緩存實現就數linkedHashmap了

 

    LinkedHashMap<Integer, String> linkedHashMap = new LinkedHashMap<>(new CountingMapData(9));
        print(linkedHashMap);
        print("=====");
        linkedHashMap = new LinkedHashMap<>(16, 0.75f, true);
        linkedHashMap.putAll(new CountingMapData(9));
        print(linkedHashMap);
        
        System.out.println("=====");
        for (int i = 0; i < 6; i++) {
            linkedHashMap.get(i);
        }
        print("--"+linkedHashMap);
        linkedHashMap.get(0);
        print("--"+linkedHashMap);

 

public class CountingMapData
extends AbstractMap<Integer,String> {
  private int size;
  private static String[] chars =
    "A B C D E F G H I J K L M N O P Q R S T U V W X Y Z"
    .split(" ");
  public CountingMapData(int size) {
    if(size < 0) this.size = 0;
    this.size = size;
  }
  private static class Entry
  implements Map.Entry<Integer,String> {
    int index;
    Entry(int index) { this.index = index; }
    public boolean equals(Object o) {
      return Integer.valueOf(index).equals(o);
    }
    public Integer getKey() { return index; }
    public String getValue() {
      return
        chars[index % chars.length] +
        Integer.toString(index / chars.length);
    }
    public String setValue(String value) {
      throw new UnsupportedOperationException();
    }
    public int hashCode() {
      return Integer.valueOf(index).hashCode();
    }
  }
  public Set<Map.Entry<Integer,String>> entrySet() {
    // LinkedHashSet retains initialization order:
    Set<Map.Entry<Integer,String>> entries =
      new LinkedHashSet<Map.Entry<Integer,String>>();
    for(int i = 0; i < size; i++)
      entries.add(new Entry(i));
    return entries;
  }
  public static void main(String[] args) {
    System.out.println(new CountingMapData(60));
  }
}

 

 

輸出：

{0=A0, 1=B0, 2=C0, 3=D0, 4=E0, 5=F0, 6=G0, 7=H0, 8=I0}
=====
{0=A0, 1=B0, 2=C0, 3=D0, 4=E0, 5=F0, 6=G0, 7=H0, 8=I0}
=====
--{6=G0, 7=H0, 8=I0, 0=A0, 1=B0, 2=C0, 3=D0, 4=E0, 5=F0}
--{6=G0, 7=H0, 8=I0, 1=B0, 2=C0, 3=D0, 4=E0, 5=F0, 0=A0}