Java多线程下解决数据安全问题

飞奔的炮台

这篇文章主要介绍了Java多线程下解决数据安全问题，本文使用代码进行讲解，可供大家学习参考
目录

• 同步代码块
  
• 同步方法
  
• lock锁
  

同步代码块
基本语句

synchronized (任意对象) {
操作共享代码
}

代码示例

public class SellTicket implements Runnable {
  private int tickets = 100;
  private Object object = new Object();
  @Override
  public void run() {
    while (true) {
      synchronized (object) {
        if (tickets > 0) {
          try {
            Thread.sleep(100);
          } catch (InterruptedException e) {
            e.printStackTrace();
          }
          System.out.println(Thread.currentThread().getName() + "正在出售第" + tickets + "张票");
          tickets--;
        }
      }
    }
  }
  public static void main(String[] args) {
    SellTicket sellTicket = new SellTicket();
    Thread thread1 = new Thread(sellTicket, "窗口1");
    Thread thread2 = new Thread(sellTicket, "窗口2");
    Thread thread3 = new Thread(sellTicket, "窗口3");
    thread1.start();
    thread2.start();
    thread3.start();
  }
}

优缺点：

• 解决了多线程的数据安全问题
  
• 多线程时，每个线程都会判断同步上的锁，耗费资源，降低了程序的运行效率
  

同步方法
同步方法：将synchronized关键字加到方法上

• 格式: 修饰符 synchronized 返回值类型 方法名(){ }
  
• 同步方法的锁对象是this
  

同步静态方法，就是把synchronized关键字加到静态方法上

• 格式: 修饰符 static synchronized 返回值类型 方法名(){ }
  
• 同步静态方法的锁对象是 类名.class
  

代码示例

public class SellTicket implements Runnable {
 
//  private int tickets = 100;
  private static int tickets = 100;
  private Object object = new Object();
  private int x = 0;
  @Override
  public void run() {
    while (true) {
      if (x % 2 == 0) {
//        synchronized (object) {
//        synchronized (this) {
        synchronized (SellTicket.class) {
          if (tickets > 0) {
            try {
              Thread.sleep(100);
            } catch (InterruptedException e) {
 
              e.printStackTrace();
 
            }            System.out.println(Thread.currentThread().getName() + "正在出售第" + tickets + "张票");
            tickets--;
          }
        }
      } else {
//        synchronized (object) {
//          if (tickets > 0) {
//            try {
//              Thread.sleep(100);
//            } catch (InterruptedException e) {
//              e.printStackTrace();
//            }
//            System.out.println(Thread.currentThread().getName() + "正在出售第" + tickets + "张票");
//            tickets--;
//          }
//        }
        sellTicket();
      }
      x++;
    }
  }
//  private void sellTicket(){
//    synchronized (object) {
//      if (tickets > 0) {
//        try {
//          Thread.sleep(100);
//        } catch (InterruptedException e) {
//          e.printStackTrace();
//        }
//        System.out.println(Thread.currentThread().getName() + "正在出售第" + tickets + "张票");
//        tickets--;
//      }
//    }
//  }
//  private synchronized void sellTicket(){
//      if (tickets > 0) {
//        try {
//          Thread.sleep(100);
//        } catch (InterruptedException e) {
//          e.printStackTrace();
//        }
//        System.out.println(Thread.currentThread().getName() + "正在出售第" + tickets + "张票");
//        tickets--;
//      }
  private static synchronized void sellTicket(){
    if (tickets > 0) {
      try {
        Thread.sleep(100);
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
      System.out.println(Thread.currentThread().getName() + "正在出售第" + tickets + "张票");
      tickets--;
    }
  }
  public static void main(String[] args) {
    SellTicket sellTicket = new SellTicket();
    Thread thread1 = new Thread(sellTicket, "窗口1");
    Thread thread2 = new Thread(sellTicket, "窗口2");
    Thread thread3 = new Thread(sellTicket, "窗口3");
    thread1.start();
    thread2.start();
    thread3.start();
  }
}

lock锁
lock实现提供比使用synchronized方法和语句可获得更广泛的操作

• void lock()获得锁
  
• void unlock()释放
  

lock是接口不能直接实例化，采用实现类实例化ReentrantLock

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public class SellTicket implements Runnable {
  private int tickets = 100;
  private Object object = new Object();
  private Lock lock = new ReentrantLock();
  @Override
  public void run() {
    while (true) {
       try {
        lock.lock();
        if (tickets > 0) {
          try {
            Thread.sleep(100);
 
          } catch (InterruptedException e) {
            e.printStackTrace();
          }
          System.out.println(Thread.currentThread().getName() + "正在出售第" + tickets + "张票");
          tickets--;
        }
      } finally {
        lock.unlock();
      }
    }
  }
  public static void main(String[] args) {
    SellTicket sellTicket = new SellTicket();
    Thread thread1 = new Thread(sellTicket, "窗口1");
    Thread thread2 = new Thread(sellTicket, "窗口2");
    Thread thread3 = new Thread(sellTicket, "窗口3");
    thread1.start();
    thread2.start();
    thread3.start();
  }<br type="_moz">

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原文链接：https://www.cnblogs.com/testero/p/15135598.html