package com.zgh.gof23.singleton;
/**
 * 餓漢式
 * @author yuelin
 *
 */
public class SingleDemo {
 private static SingleDemo instance = new SingleDemo();
 //私有化構(gòu)造器
 private SingleDemo() {
 //防止其他通過(guò)反射調(diào)用構(gòu)造方法，破解單例
 if (instance != null) {
  throw new RuntimeException();
 }
 }

 //對(duì)外提供統(tǒng)一的訪問(wèn)點(diǎn)
 public static SingleDemo getInstance() {
 return instance;
 }
}

package com.zgh.gof23.singleton;

/**
 * 懶漢式實(shí)現(xiàn)單例
 * 
 * @author zhuguohui
 *
 */
public class SingleDemo2 {
 // 此處并不初始化實(shí)例
 private static SingleDemo2 instance;

 private SingleDemo2() {
 if (instance != null) {
  throw new RuntimeException();
 }
 }

 /**
 * 當(dāng)調(diào)用此方法的時(shí)候才初始化實(shí)例， 為了實(shí)現(xiàn)線程安全，需要使用同步方法
 * 
 * @return
 */
 public static synchronized SingleDemo2 getInstance() {
 if (instance == null) {
  instance = new SingleDemo2();
 }
 return instance;
 }
}

package com.zgh.gof23.singleton;

/**
 * 雙重檢查
 * 
 * @author zhuguohui
 *
 */
public class SingleDemo3 {
 private static SingleDemo3 instance;

 private SingleDemo3() {
 if (instance != null) {
  throw new RuntimeException();
 }
 }

 public static SingleDemo3 getInstance() {
 //第一重檢查，提高效率
 if (instance == null) {
  synchronized (SingleDemo3.class) {
  //第二重檢查保證線程安全
  if (instance == null) {
   instance = new SingleDemo3();
  }
  }
 }
 return instance;
 }
}

/**
 * 靜態(tài)內(nèi)部類(lèi)實(shí)現(xiàn)單例
 * 
 * @author zhuguohui
 *
 */
public class SingleDemo4 {
 private static SingleDemo4 instance;

 private static class SingleDemo4Holder {
 private static final SingleDemo4 instance = new SingleDemo4();
 }

 private SingleDemo4() {
 if (instance != null) {
  throw new RuntimeException();
 }
 }

 /**
 * 調(diào)用這個(gè)方法的時(shí)候，JVM才加載靜態(tài)內(nèi)部類(lèi)，才初始化靜態(tài)內(nèi)部類(lèi)的類(lèi)變量。由于由JVM初始化，保證了線程安全性，
 * 同時(shí)又實(shí)現(xiàn)了懶加載
 * @return
 */
 public static SingleDemo4 getInstance() {
 return SingleDemo4Holder.instance;
 }
}

/**
 * 枚舉實(shí)現(xiàn)單例
 * 枚舉由JVM實(shí)現(xiàn)其的單例性
 * @author zhuguohui
 *
 */
public enum SingleDemo5 {
 INSTANCE;
}

public class APP {
 public static void main(String[] args) {

 int threadCount = 100;
 long start = System.currentTimeMillis();
 final CountLock lock = new CountLock(threadCount);
 for (int i = 0; i < threadCount; i++) {
  new Thread(new Runnable() {

  @Override
  public void run() {
   for (int j = 0; j < 10000000; j++) {
   //通過(guò)更換此處，來(lái)測(cè)試不同單例實(shí)現(xiàn)方式在多線程環(huán)境下的性能
   SingleDemo5 demo = SingleDemo5.INSTANCE;
   }
   lock.finish();
  }
  }).start();

 }
 //等待所有線程執(zhí)行完
 lock.waitForWrok();
 long end = System.currentTimeMillis();
 System.out.println("總共耗時(shí)" + (end - start));
 }
}

package com.zgh.gof23.singleton;

public class CountLock {
 //線程的總數(shù)量
 private int count;

 public CountLock(int count) {
 this.count = count;
 }

 /**
 * 當(dāng)一個(gè)線程完成任務(wù)以后，調(diào)用一次這個(gè)方法
 */
 public synchronized void finish() {
 count--;
 if (count == 0) {
  notifyAll();
 }
 }

 /**
 * 需要等待其他線程執(zhí)行完的線程，調(diào)用此方法。
 */
 public synchronized void waitForWrok() {
 while (count > 0) {
  try {
  wait();
  } catch (InterruptedException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
  }
 }
 }
}