Java如何判断线程是否结束的三种方法

import java.util.concurrent.ExecutorService;  
import java.util.concurrent.Executors;  

public class Test {  
 
    public static void main(String args[]) throws InterruptedException {  
        ExecutorService exe = Executors.newFixedThreadPool(50);  
        for (int i = 1; i <= 5; i++) {  
            exe.execute(new SubThread(i));  
        }  
        exe.shutdown();  
        while (true) {  
            if (exe.isTerminated()) {  
                System.out.println("结束了！");  
                break;  
            }  
            Thread.sleep(200);  
        }  
    }  
}

public class CountDownLatchApproach {undefined
    public static void main(String[] args) throws IOException, InterruptedException {undefined
        final int nThreads = 10;
        final CountDownLatch endGate = new CountDownLatch(nThreads);
        final File stream = new File("c:\\temp\\stonefeng\\stream.txt");
        final OutputStream os = new FileOutputStream(stream);
        final OutputStreamWriter writer = new OutputStreamWriter(os);
        ExecutorService exec = Executors.newCachedThreadPool();
        for (int i = 0; i < nThreads; i++) {undefined
            final int num = i;
            Runnable task = new Runnable() {undefined
                @Override
                public void run() {undefined
                    try {undefined
                        writer.write(String.valueOf(num)+"\n");
                    } catch (IOException e) {undefined
                        e.printStackTrace();
                    } finally {undefined
                        endGate.countDown();
                    }
                }
            };
            exec.submit(task);
        }
        endGate.await();
        writer.write("---END---\n");
        writer.close();
    }
}