java的多线程与并发

java创建线程

• extend Thread
• implements Runnable

java多线程计算器

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

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

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

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

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

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