import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; /*  * Lock lock = new ReentrantLock();  * lock.lock();  lock.unLock();  * 類似于 synchronized，但不能與synchronized 混用  */ public class LockTest {   public static void main(String[] args) {     final Outer outer = new LockTest().new Outer();     new Thread(new Runnable() {        @Override       public void run() {         // TODO Auto-generated method stub         while (true) {           outer.out1("zhangxiaoxiao");           outer.out2("lihuoming");         }       }      }).start();     new Thread(new Runnable() {        @Override       public void run() {         // TODO Auto-generated method stub         while (true) {           outer.out1("zhangxiaoxiao");           outer.out2("lihuoming");         }       }      }).start();    }   class Outer {     Lock lock = new ReentrantLock();     void out1(String name) {       lock.lock();       int len = name.length();       for (int i = 0; i < len; i++) {         System.out.print(name.charAt(i));       }       System.out.println();       lock.unlock();     }     void out2(String name) {       lock.lock();       int len = name.length();       for (int i = 0; i < len; i++) {         System.out.print(name.charAt(i));       }       System.out.println();       lock.unlock();     }   } } 

import java.util.HashMap; import java.util.Map; import java.util.concurrent.locks.ReadWriteLock; import java.util.concurrent.locks.ReentrantReadWriteLock; /*  * 問題：設計一個 緩存機制 的 偽代碼  *  從集合中讀取數據，讀取不到，就寫入，再考慮多線程并發的情況   */ public class ReadWriteLockTest2 {   private Map<String, Object> data = new HashMap<String, Object>();   private ReadWriteLock lock = new ReentrantReadWriteLock();    //讀寫鎖   public Object getInstance1(String key, Object obj) {     lock.readLock().lock();     Object value = null;     try {       value = data.get(key);       if (value == null) {//一條線程進入這里，         lock.readLock().unlock();//讀鎖解了，其他線程就可能也到這了         lock.writeLock().lock();//只能有一條線程到這，寫鎖開啟，要寫入數據了         if (data.get(key) == null) {           value = obj;               /*先判斷數據，如果不存在，才寫入，，因為 界時當寫鎖解除后，其他               線程，再想寫入時， 判斷到數據存在 ，就跳過了。就不會發生同時寫入的情況             */              data.put(key, value);          }         lock.writeLock().unlock();//寫完了，解鎖         lock.readLock().lock();       }     } finally {       lock.readLock().unlock();     }       return value;   }