4线程，2个对i加，2个对i减

package test1;


/**
 * 设计4个线程，其中2个线程，每次对i加1，另外两个线程，每次对i减一
 * 
 * @author Administrator
 *
 */
public class Thread2 {
  public static void main(String[] args) {
    ShareData d = new ShareData();
    for (int i = 0; i < 2; i++) {
      new Thread(new Runnable1(d)).start();
      new Thread(new Runnable2(d)).start();
    }
  }
}

/**
 * 加
 * @author Administrator
 *
 */
class Runnable1 implements Runnable {
  private ShareData d;
  public Runnable1 (ShareData d) {
    this.d = d;
  }
  
  @Override
  public void run() {
    d.increment();
  }
}

/**
 * 减
 * @author Administrator
 *
 */
class Runnable2 implements Runnable {
  private ShareData d;
  public Runnable2 (ShareData d) {
    this.d = d;
  }
  
  @Override
  public void run() {
    d.decrement();
  }
}


class ShareData {

  private int i = 0;
  
  public synchronized void increment () {
    i++;
    System.out.println("加后i为：" + i);
  }
  
  public synchronized void decrement () {
    i--;
    System.out.println("减后i为：" + i);
  }
}