三大线程不安全案例

三大不安全案例

• 买票问题

  //买票
  public class Demo01 {
      public static void main(String[] args) {
          BuyTickets buyTickets = new BuyTickets();
          new Thread(buyTickets,"person1").start();
          new Thread(buyTickets,"person2").start();
          new Thread(buyTickets,"person3").start();
      }
  }
  class BuyTickets implements Runnable{
      private int ticketNum = 20;
      boolean flag = true;
      @Override
      public void run() {
          while (flag){
              try {
                  buy();
              } catch (Exception e) {
                  e.printStackTrace();
              }
          }
      }
  
      private void buy() throws Exception {
          //判断是否有票
          if (ticketNum < 1){
              flag = false;
              return;
          }
          //模拟延时
          Thread.sleep(100);
          //买票
          System.out.println(Thread.currentThread().getName()+"第"+ticketNum--+"张票");
      }
  }
  //person2第10张票
  person3第9张票
  person1第8张票
  person2第7张票
  person1第6张票
  person3第6张票
  person1第4张票
  person3第3张票
  person2第5张票
  person3第2张票
  person1第1张票
  person2第0张票
  person3第-1张票
  

• 不安全取款

  //不安全取款
  public class Demo02 {
      public static void main(String[] args) {
          //账户
          Account account = new Account(100,"A");
          Bank person1 = new Bank(account, 20, "Person1");
          Bank person2 = new Bank(account, 90, "person2");
          person1.start();
          person2.start();
      }
  }
  //账户
  class Account{
      int money;
      String name;
  
      public Account(int money, String name) {
          this.money = money;
          this.name = name;
      }
  }
  //银行
  class Bank extends Thread{
      Account account;
      int outMoney;
      int nowMoney;
      public Bank(Account account,int outMoney,String name){
          super(name);
          this.outMoney = outMoney;
          this.account = account;
      }
  
      @Override
      public void run() {
          //判断是否还有钱
          if(account.money-outMoney<0){
              System.out.println(Thread.currentThread().getName()+"钱不够了");
              return;
          }
          //sleep可以放大问题的发生性
          try {
              Thread.sleep(1000);
          } catch (InterruptedException e) {
              e.printStackTrace();
          }
  
          //卡内余额
          account.money = account.money - outMoney;
          //手里的钱
          nowMoney = nowMoney +outMoney;
          System.out.println(account.name+"余额为："+account.money);
          //Thread.currentThread().getName() =  this.getName()
          System.out.println(this.getName()+"手里的钱"+nowMoney);
      }
  //A余额为：-10
  Person1手里的钱20
  A余额为：-10
  person2手里的钱90    
  

• 线程不安全集合

  //线程不安全集合
  public class Demo03 {
      public static void main(String[] args) throws InterruptedException {
          final ArrayList<String> arrayList = new ArrayList<String>();
          for (int i = 0; i < 10000; i++) {
              new Thread(()->{
                  arrayList.add(Thread.currentThread().getName());
              }).start();
          }
          Thread.sleep(3000);
          System.out.println(arrayList.size());
      }
  }
  
  //9984