多线程加锁练习

矫情吗；* 2022-10-18 15:57 198阅读 0赞

## 练习一 ##

未加锁的多线程：

package SYN;
    
    //不安全的取钱
    public class UnsafeBank { 
        public static void main(String[] args) { 
           Account account = new Account(100, "结婚基金");
    
            Drawing you = new Drawing(account, 50, "你");
            Drawing girlFriend = new Drawing(account, 100, "girlFriens");
    
            you.start();;
            girlFriend.start();
    
    
        }
    }
    
    //账户
    class Account{ 
        int money;
        String name;
    
        public Account(int money, String name){ 
            this.money = money;
            this.name = name;
        }
    }
    
    //银行：模拟取钱
    class  Drawing extends Thread{ 
    
        Account account;//账户
        //取了多少钱
         int drawingMoney;
         //现在手里还有多少钱
         int nowMoney;
    
         public Drawing(Account account, int drawingMoney, String name){ 
             super(name);
             this.account = account;
             this.drawingMoney = drawingMoney;
    
         }
    
         //取钱
        //synchronized 默认锁的是 this
        @Override
        public void run(){ 
    
    
                 if(account.money - drawingMoney < 0){ 
                     System.out.println(Thread.currentThread().getName() + "余额不够");
                     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 = 余额 - 取出的钱
                 account.money = account.money - drawingMoney;
    
                 //你手里的钱
                 nowMoney = nowMoney + drawingMoney;
    
                 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);
    
         }
    
    
    }

结果：我取到钱，girlfriend也取到钱，卡内余额为负数！

加过锁后：

//不安全的取钱 
    public class UnsafeBank {                                                           
        public static void main(String[] args) {                                        
           Account account = new Account(100, "结婚基金");                                 
                                                                                       
            Drawing you = new Drawing(account, 50, "你");                               
            Drawing girlFriend = new Drawing(account, 100, "girlFriens");              
                                                                                       
            you.start();;                                                              
            girlFriend.start();                                                        
                                                                                       
                                                                                       
        }                                                                              
    }                                                                                  
                                                                                       
    //账户 
    class Account{                                                                      
        int money;                                                                     
        String name;                                                                   
                                                                                       
        public Account(int money, String name){                                         
            this.money = money;                                                        
            this.name = name;                                                          
        }                                                                              
    }                                                                                  
                                                                                       
    //银行：模拟取钱 
    class  Drawing extends Thread{                                                      
                                                                                       
        Account account;//账户 
        //取了多少钱 
         int drawingMoney;                                                             
         //现在手里还有多少钱 
         int nowMoney;                                                                 
                                                                                       
         public Drawing(Account account, int drawingMoney, String name){                
             super(name);                                                              
             this.account = account;                                                   
             this.drawingMoney = drawingMoney;                                         
                                                                                       
         }                                                                             
                                                                                       
         //取钱 
        //synchronized 默认锁的是 this 
        @Override                                                                      
        public void run(){                                                              
             
             //加入锁 
             synchronized (account) {                                                   
                 if(account.money - drawingMoney < 0){                                  
                     System.out.println(Thread.currentThread().getName() + "余额不够");    
                     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 = 余额 - 取出的钱 
                 account.money = account.money - drawingMoney;                         
                                                                                       
                 //你手里的钱 
                 nowMoney = nowMoney + drawingMoney;                                   
                                                                                       
                 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);               
                                                                                       
             }                                                                         
        }                                                                              
                                                                                       
    }

结果正常

## 练习二、 ##

import java.util.ArrayList;
    import java.util.List;
    
    public class UnfaseList { 
    
        public static void main(String[] args) { 
    
            List<String> list = new ArrayList<>();
            for(int i = 0; i < 10000; i++){ 
                new Thread(()->{ 
                   list.add(Thread.currentThread().getName());
                }).start();
            }
            try { 
                Thread.sleep(1000);
            }  catch (InterruptedException e){ 
                e.printStackTrace();
            }
    
            System.out.println(list.size());
        }
    }

加锁后：

import java.util.ArrayList;
    import java.util.List;
    
    public class UnfaseList { 
    
        public static void main(String[] args) { 
    
            List<String> list = new ArrayList<>();
            for(int i = 0; i < 10000; i++){ 
                new Thread(()->{ 
                    synchronized (list){ 
                        list.add(Thread.currentThread().getName());
                    }
                }).start();
            }
            try { 
                Thread.sleep(1000);
            }  catch (InterruptedException e){ 
                e.printStackTrace();
            }
    
            System.out.println(list.size());
        }
    }

结果正常。