1 package mystudy; 2  3 public class ManyThreads { 4  5     private int j; 6  7     public static void main(String[] args) { 8         // TODO Auto-generated method stub 9         ManyThreads many = new ManyThreads();10         Inc inc = many.new Inc();11         Dec dec = many.new Dec();12         for (int i = 0; i < 2; i++) {13             Thread t = new Thread(inc);14             t.start();15             t = new Thread(dec);16             t.start();17         }18     }19 20     private synchronized void inc() {21         j++;22         System.out.println(Thread.currentThread().getName() + "inc" + j);23     }24 25     private synchronized void dec() {26         j--;27         System.out.println(Thread.currentThread().getName() + "dec" + j);28     }29 30     class Inc implements Runnable {31 32         @Override33         public void run() {34             // TODO Auto-generated method stub35             for (int i = 0; i < 20; i++) {36                 inc();37             }38         }39 40     }41 42     class Dec implements Runnable {43 44         @Override45         public void run() {46             // TODO Auto-generated method stub47             for (int i = 0; i < 20; i++) {48                 dec();49             }50         }51 52     }53 }