java的多线程与并发

cloud

java创建线程

  • extend Thread
  • implements Runnable

java多线程计算器

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
class Caculator implements Runnable{
    public void run(){
          for(int i = 0; i < 100; i ++){
              System.out.println(“%s, value=%d”, Thread.currentThread().getName(), i);
        }
     }
}

class Application{
    public static void main(){
        for(int i = 0; i < 10; i ++){
                Caculator c = new Caculator();
                Thread t =  new Thread(c);
                t.start();
         }
    }
}

计数器

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
public class Counter implements Runnable{
    private int count = 0;
    public void run(){
        for (int i = 0; i < 10000; i ++){
            count ++;
        }
    }

     public static int getCountValue(){
        return count;
    }
}

public class Application{
    public static void main(){
        Counter c = new Counter();
         Thread t = new Thread();
        t.start();
        System.out.println(Count.getCountValue());
    }
}

使用join方法

  • 子线程调用join方法，让main线程等待
    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    13
    14
    15
    16
    public class MySubThread extends Thread{
        public void run(){
            int sleepTime = 2000;
            Thread.sleep(sleepTime);
            System.out.println(“MySubThread run finished!”);
        }
    }

    public class Application{
        public static void main(){
            MySubThread t = new MySubThread();
            t.start();
            // t.join();
            System.out.println(“Main Thread finished!”);
        }
    }

线程上锁

  • synchronized
  • lock与ReentrantedLock

synchronized版本的计数器

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
public class Counter implements Runnable{
    int count = 0;
    
    public static int getCount(){
        return count;
    }
    
    @Override
    public void run(){
        for(int i = 0; i < 10000; i ++){
            synchronized(this){
                count ++;
            }
        } 
    }
}

public class Application{
    public static void main(){
        Counter c = new Counter();
        Thread t1 = new Thread();
        Thread t2 = new Thread();
        t1.start();
        t1.join();
        t2.start();
        t2.join();
        System.out.println(“count is: ” + Count.getCount());
    }
}

synchronized版本的计数器之二， 使用synchronized给实例方法加锁

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
public class Counter implements Runnable{
    int count = 0;
    
    public static int getCount(){
        return count;
    }
    
    @Override
    public synchronized void run(){
        for(int i = 0; i < 10000; i ++){
                count ++;
        } 
    }
}

public class Application{
    public static void main(){
        Counter c = new Counter();
        Thread t1 = new Thread();
        Thread t2 = new Thread();
        t1.start();
        t1.join();
        t2.start();
        t2.join();
        System.out.println(“count is: ” + Count.getCount());
    }
}

synchronized版本的计数器之三，使用synchronized修饰静态方法

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
public class Counter implements Runnable{
    int count = 0;
    
    public static int getCount(){
        return count;
    }
    
    @Override
    public void run(){
        for(int i = 0; i < 10000; i ++){
                increase();
            }
        } 
    }

    public static synchronize increase(){
        count ++;
    }
}

public class Application{
    public static void main(){
        Counter c = new Counter();
        Thread t1 = new Thread();
        Thread t2 = new Thread();
        t1.start();
        t1.join();
        t2.start();
        t2.join();
        System.out.println(“count is: ” + Count.getCount());
    }
}

笔记

  • reentrant单词也作re-entrant，entrant为进入者、新会员的意思