Java如何實現(xiàn)多線程及線程安全

/**
 * 
 * @version: 1.1.0
 * @Description: 多線程
 * @author: wsq
 * @date: 2020年6月8日下午2:25:33
 */
public class MyThread extends Thread{
@Override
public void run() {
  System.out.println("This is the first thread!");
}
public static void main(String[] args) {
  MyThread mt = new MyThread();
  mt.start();
}
}

public class MultithreadingTest {
public static void main(String[] args) {
  new Thread(() -> System.out.println("This is the first thread!")).start();
}
}

public class MyThreadImpl implements Runnable{
private int count = 5;
  @Override
  public void run() {
    // TODO Auto-generated method stub
    count--;
    System.out.println("Thread"+Thread.currentThread().getName()+"count:"+count);
  }
}

/**
 * 
 * @version: 1.1.0
 * @Description: 測試類
 * @author: wsq
 * @date: 2020年6月8日下午9:27:02
 */
public class Test {
  public static void main(String[] args) {
    MyThreadImpl myThreadImpl = new MyThreadImpl();
    Thread A = new Thread(myThreadImpl,"A");
    Thread B = new Thread(myThreadImpl,"B");
    Thread C = new Thread(myThreadImpl,"C");
    Thread D = new Thread(myThreadImpl,"D");
    Thread E = new Thread(myThreadImpl,"E");
    A.start();
    B.start();
    C.start();
    D.start();
    E.start();
  }
}

public class MyThreadImpl implements Runnable{
private int count = 5;
  @Override
　　// 使用同步解決線程安全問題
  synchronized public void run() {
    // TODO Auto-generated method stub
    count--;
    System.out.println("Thread"+Thread.currentThread().getName()+"count:"+count);
  }
}