Android LRU算法中LinkedHashMap补充 <11>

上一篇提到LRUCache.java文件中涉及到下面的变量参数,说的不是太清楚,下面是单独的事例补充一下.

private int maxSize;

另外,如果让LinkedHashMap移除超出的部分,比如设置maxSize=10,结果向里面put了12对象,那么其中就要为了保证只有10个对象,就需要移除多余的两个,LinkedHashMap设计的是移除最先put进来的那那个对象,也就是第一和第二个put进来的那两个对象.

/**
     * Removes the entry for {@code key} if it exists.
     *
     * @return the previous value mapped by {@code key}.
     */
    public final V remove(K key) {
        if (key == null) {
            throw new NullPointerException("key == null");
        }

        V previous;
        synchronized (this) {
            previous = map.remove(key);
            if (previous != null) {
                size -= safeSizeOf(key, previous);
            }
        }

        if (previous != null) {
            entryRemoved(false, key, previous, null);
        }

        return previous;
    }

下面在上一篇的基础上再进一步的程序调整:

DurianUtil.java

package org.durian.durianlrubitmap.util;

import android.util.Log;

import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;

/**
 * Project name : DurianLRUBitmap
 * Created by zhibao.liu on 2016/1/13.
 * Time : 18:33
 * Email [email protected]
 * Action : durian
 */
public class DurianUtil {

    private final static String TAG="DurianUtil";

    private final static int LINKED_MAX=10;
    public static void DurianLinkedHashMap(){

        Map<Integer,String> map=new LinkedHashMap<Integer, String>();
        map.put(5,"hello,zhibao.liu");
        map.put(8,"hello,world !");
        map.put(3,"hello,java programe !");

        for (Iterator it=map.keySet().iterator();it.hasNext();){
            Object key=it.next();
            Log.i(TAG,"link key : "+key.toString());
        }

        Log.i(TAG,"++++++++++++++++++++++++++++++++++++++++++++");
        LinkedHashMap<Integer,String> linkmap=new LinkedHashMap<Integer, String>(LINKED_MAX,0.75f,false){
            @Override
            protected boolean removeEldestEntry(Entry<Integer, String> eldest) {
                return this.size()>LINKED_MAX;
//                return super.removeEldestEntry(eldest);
            }
        };

        for (int i=0;i<12;i++){
            linkmap.put(i,"i="+i);
        }
        for (Iterator it=linkmap.keySet().iterator();it.hasNext();){
            Object key=it.next();
            Log.i(TAG,"linkmap key : "+key.toString());
        }

        Log.i(TAG,"#########################################");

        DurianLinkedHashMap<Integer,String> durianLinkedHashMap=new DurianLinkedHashMap<Integer, String>();
        durianLinkedHashMap.setLINK_HASHMAP_MAX_SIZE(10);
        for (int i=0;i<12;i++){
            durianLinkedHashMap.put(i,"i = "+i);
        }

        for(Iterator it=durianLinkedHashMap.keySet().iterator();it.hasNext();){
            Object key=it.next();
            Log.i(TAG,"durianLinkedHashMap : "+key.toString());
        }

        Log.i(TAG,"durianLinkedHashMap MAX : "+durianLinkedHashMap.getLINK_HASHMAP_MAX_SIZE());

        Log.i(TAG,"******************************************");

        Map<Integer,String> hashmap=new HashMap<Integer, String>();
        hashmap.put(5,"hello,zhibao.liu");
        hashmap.put(8,"hello,world !");
        hashmap.put(3,"hello,java programe !");

        for (Iterator it=hashmap.keySet().iterator();it.hasNext();){
            Object key=it.next();

            Log.i(TAG,"hash key : "+key.toString());

        }

    }

}

主要查看上面代码的一段如下:

protected boolean removeEldestEntry(Entry<Integer, String> eldest) {
                return this.size()>LINKED_MAX;
//                return super.removeEldestEntry(eldest);
            }

这个返回值,如果返回的是false,LinkedHashMap将不会进行移除最先put进来的,当返回是true时,LinkedHashMap就会进行移除超出MAX size的部分,移除最先put进来的对象.

DurianLinkedHashMap.java

package org.durian.durianlrubitmap.util;

import java.util.LinkedHashMap;
import java.util.Map;

/**
 * Project name : DurianLRUBitmap
 * Created by zhibao.liu on 2016/1/14.
 * Time : 13:46
 * Email [email protected]
 * Action : durian
 */
public class DurianLinkedHashMap<V,T> extends LinkedHashMap {

    private int LINK_HASHMAP_MAX_SIZE=0;

    public void setLINK_HASHMAP_MAX_SIZE(int max){
        LINK_HASHMAP_MAX_SIZE=max>=0?max:0;
    }

    public int getLINK_HASHMAP_MAX_SIZE(){

        return LINK_HASHMAP_MAX_SIZE;

    };

    @Override
    protected boolean removeEldestEntry(Entry eldest) {
//        return super.removeEldestEntry(eldest);
        return this.size()>LINK_HASHMAP_MAX_SIZE;
    }
}

上面的这个条件可以自行设定,还可以增加其他判断条件来处理是否移除最先put进来的.

运行结果如下: