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Java - 執行緒連線

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建立 Thread 物件後，可以透過呼叫 start() 方法來啟動它，該方法會執行對 run() 方法的呼叫。在多個執行緒執行的情況下，我們可以阻塞當前執行緒，直到另一個執行緒終止。

Java 中的執行緒連線

Java 中的執行緒連線是指等待（或阻塞）一個執行緒，直到另一個執行緒完成其執行。 Thread 類的 join() 方法用於此目的。

語法

以下是 join() 方法的簡單語法：

void join();

過載的 Thread.join() 方法

以下是三個過載的 join() 方法：

join() - 當前執行緒在第二個執行緒上呼叫此方法，導致當前執行緒阻塞，直到第二個執行緒終止。
join(long millisec) - 當前執行緒在第二個執行緒上呼叫此方法，導致當前執行緒阻塞，直到第二個執行緒終止或指定的毫秒數過去。
join(long millisec, int nanos) - 當前執行緒在第二個執行緒上呼叫此方法，導致當前執行緒阻塞，直到第二個執行緒終止或指定的毫秒數 + 納秒數過去。

Java 中執行緒連線的示例

在此示例中，我們透過實現 Runnable 介面建立一個 RunnableDemo 類。RunnableDemo 類具有 run() 方法的實現。在主類 TestThread 中，我們建立了 RunnableDemo 物件，並使用這些物件建立了兩個 Thread 物件。當在每個執行緒物件上呼叫 Thread.start() 方法時，執行緒開始處理並執行程式。使用 join() 方法，我們阻塞當前執行緒，以確保一旦一個執行緒完成，只有下一個執行緒才會啟動。

package com.tutorialspoint;

class RunnableDemo implements Runnable {
   RunnableDemo( ) {
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: New");
   }

   public void run() {
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: Running");
      for(int i = 4; i > 0; i--) {
         System.out.println("Thread: " + Thread.currentThread().getName() + ", " + i);         
      }
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: Dead");
   }
}

public class TestThread {
   public static void main(String args[]) throws InterruptedException {
      Thread t1 = new Thread( new RunnableDemo(), "Thread-1");
      Thread t2 = new Thread( new RunnableDemo(), "Thread-2");
      Thread t3 = new Thread( new RunnableDemo(), "Thread-3");
      // start t1 thread and join main thread
      t1.start();
      t1.join();	  
      // t2 will start when t1 is dead
      t2.start();        
      t2.join();
      // t3 will start when t2 is dead
      t3.start();
   }
}

輸出

Thread: Thread-1, State: New
Thread: Thread-2, State: New
Thread: Thread-1, State: Running
Thread: Thread-1, 4
Thread: Thread-1, 3
Thread: Thread-1, 2
Thread: Thread-1, 1
Thread: Thread-1, State: Dead
Thread: Thread-2, State: Running
Thread: Thread-2, 4
Thread: Thread-2, 3
Thread: Thread-2, 2
Thread: Thread-2, 1
Thread: Thread-2, State: Dead

Java 中執行緒連線的更多示例

示例 1

在此示例中，我們透過實現 Runnable 介面建立一個 RunnableDemo 類。RunnableDemo 類具有 run() 方法的實現。在主類 TestThread 中，我們建立了 RunnableDemo 物件，並使用這些物件建立了兩個 Thread 物件。當在每個執行緒物件上呼叫 Thread.start() 方法時，執行緒開始處理並執行程式。使用 join(long millisec) 方法，我們將當前執行緒阻塞 200 毫秒，以確保一旦一個執行緒完成或延遲 200 毫秒後，只有下一個執行緒才會啟動。

package com.tutorialspoint;

class RunnableDemo implements Runnable {
   RunnableDemo( ) {
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: New");
   }

   public void run() {
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: Running");
      for(int i = 4; i > 0; i--) {
         try {
            Thread.sleep(50);
         } catch (InterruptedException e) {
            // TODO Auto-generated catch block
         e.printStackTrace();
         }
         System.out.println("Thread: " + Thread.currentThread().getName() + ", " + i);         
      }
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: Dead");
   }
}

public class TestThread {
   public static void main(String args[]) throws InterruptedException {
      Thread t1 = new Thread( new RunnableDemo(), "Thread-1");
      Thread t2 = new Thread( new RunnableDemo(), "Thread-2");
      Thread t3 = new Thread( new RunnableDemo(), "Thread-3");
      // start t1 thread and join main thread
      t1.start();
      t1.join(200);	  
      // t2 will start when t1 is dead or 200 ms is elapsed
      t2.start();        
      t2.join(200);
      // t3 will start when t2 is dead or 200 ms is elapsed
      t3.start();
   }
}

輸出

Thread: main, State: New
Thread: main, State: New
Thread: main, State: New
Thread: Thread-1, State: Running
Thread: Thread-1, 4
Thread: Thread-1, 3
Thread: Thread-1, 2
Thread: Thread-2, State: Running
Thread: Thread-1, 1
Thread: Thread-1, State: Dead
Thread: Thread-2, 4
Thread: Thread-2, 3
Thread: Thread-2, 2
Thread: Thread-3, State: Running
Thread: Thread-2, 1
Thread: Thread-2, State: Dead
Thread: Thread-3, 4
Thread: Thread-3, 3
Thread: Thread-3, 2
Thread: Thread-3, 1
Thread: Thread-3, State: Dead

示例 2

在此示例中，我們透過實現 Runnable 介面建立一個 RunnableDemo 類。RunnableDemo 類具有 run() 方法的實現。在主類 TestThread 中，我們建立了 RunnableDemo 物件，並使用這些物件建立了兩個 Thread 物件。當在每個執行緒物件上呼叫 Thread.start() 方法時，執行緒開始處理並執行程式。使用 join(long millisec, long nanoseconds) 方法，我們將當前執行緒阻塞 200 毫秒和 100000 納秒，以確保一旦一個執行緒完成或延遲 201 毫秒後，只有下一個執行緒才會啟動。

package com.tutorialspoint;

class RunnableDemo implements Runnable {
   RunnableDemo( ) {
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: New");
   }

   public void run() {
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: Running");
      for(int i = 4; i > 0; i--) {
         try {
            Thread.sleep(49);
         } catch (InterruptedException e) {
            // TODO Auto-generated catch block
         e.printStackTrace();
         }
         System.out.println("Thread: " + Thread.currentThread().getName() + ", " + i);         
      }
      System.out.println("Thread: " + Thread.currentThread().getName() + ", " + "State: Dead");
   }
}

public class TestThread {
   public static void main(String args[]) throws InterruptedException {
      Thread t1 = new Thread( new RunnableDemo(), "Thread-1");
      Thread t2 = new Thread( new RunnableDemo(), "Thread-2");
      Thread t3 = new Thread( new RunnableDemo(), "Thread-3");
      
      // start t1 thread and join main thread
      t1.start();
      t1.join(200,100000);	  
      
      // t2 will start when t1 is dead or 201 ms is elapsed
      t2.start();        
      t2.join(200,100000);
      
      // t3 will start when t2 is dead or 201 ms is elapsed
      t3.start();
   }
}

輸出

Thread: main, State: New
Thread: main, State: New
Thread: main, State: New
Thread: Thread-1, State: Running
Thread: Thread-1, 4
Thread: Thread-1, 3
Thread: Thread-1, 2
Thread: Thread-1, 1
Thread: Thread-1, State: Dead
Thread: Thread-2, State: Running
Thread: Thread-2, 4
Thread: Thread-2, 3
Thread: Thread-2, 2
Thread: Thread-2, 1
Thread: Thread-2, State: Dead
Thread: Thread-3, State: Running
Thread: Thread-3, 4
Thread: Thread-3, 3
Thread: Thread-3, 2
Thread: Thread-3, 1
Thread: Thread-3, State: Dead

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