Find the inner class

[Nikolaos Plastiras]

When I compile this code it outputs PingPong.class , PingPong$MyThread.class and PingPong$1.class
The first and second I understand, but I don't understand why it outputs PingPong$1.class since there is no anonymous inner class. Or is there?..
This is the PingPong.java file:

public class PingPong {
	
	private class MyThread extends Thread {
		boolean isPing;		//variable to determine ping or pong
		Object lock;		//variable used only for synchronization
		
		private MyThread(Object lock, boolean isPing) {
			this.lock = lock;
			this.isPing = isPing;
		}
		
		public void pingPong() {
			synchronized(lock) {
				for(int i=0;i<10;i++) {		//play ten times
					if(isPing)
						System.out.println("Ping");
					else
						System.out.println("    Pong");
					lock.notifyAll();		//notify next player to play
					try {
						lock.wait();		//wait for your turn
					} catch(Exception e) {
						e.printStackTrace();
					}
				}
			lock.notifyAll();		//release last player
			}
		}
		
		public void run() {
			pingPong();
		}
	}
	
	public static void main(String[] args) {
		PingPong game = new PingPong();
		Object o = new Object();
		System.out.println("Ready... set... Go!\n");
		Thread Ping = game.new MyThread(o,true);		//ping player
		Thread Pong = game.new MyThread(o,false);		//pong player
		Ping.start();		//new thread starts
		Pong.start();		//new thread starts
		try {
			Ping.join();		//wait for players to end
			Pong.join();		//
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		System.out.println("\nDone!");
	}
}

[Henry Wong]

Nikolaos Plastiras wrote:When I compile this code it outputs PingPong.class , PingPong$MyThread.class and PingPong$1.class
The first and second I understand, but I don't understand why it outputs PingPong$1.class since there is no anonymous inner class. Or is there?..
This is the PingPong.java file:

public class PingPong {
	
	private class MyThread extends Thread {
		boolean isPing;		//variable to determine ping or pong
		Object lock;		//variable used only for synchronization
		
		private MyThread(Object lock, boolean isPing) {
			this.lock = lock;
			this.isPing = isPing;
		}
		
		public void pingPong() {
			synchronized(lock) {
				for(int i=0;i<10;i++) {		//play ten times
					if(isPing)
						System.out.println("Ping");
					else
						System.out.println("    Pong");
					lock.notifyAll();		//notify next player to play
					try {
						lock.wait();		//wait for your turn
					} catch(Exception e) {
						e.printStackTrace();
					}
				}
			lock.notifyAll();		//release last player
			}
		}
		
		public void run() {
			pingPong();
		}
	}
	
	public static void main(String[] args) {
		PingPong game = new PingPong();
		Object o = new Object();
		System.out.println("Ready... set... Go!\n");
		Thread Ping = game.new MyThread(o,true);		//ping player
		Thread Pong = game.new MyThread(o,false);		//pong player
		Ping.start();		//new thread starts
		Pong.start();		//new thread starts
		try {
			Ping.join();		//wait for players to end
			Pong.join();		//
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		System.out.println("\nDone!");
	}
}

Perhaps it is residue from an old incarnation of the class. Did you used to have an anonymous class? If you delete the class files, and recompile again, does it reappear?

Henry

[Dan Drillich]

Henry Wong wrote:

Perhaps it is residue from an old incarnation of the class. Did you used to have an anonymous class? If you delete the class files, and recompile again, does it reappear?

Henry

I also see these three classes and I just compiled it for the first time.

Regards,
Dan

[Paul Clapham]

I just compiled it and ran it (in Eclipse) and it completed successfully. And I don't see the PingPong$1.class in the compiled classes folder with the other two.

By the way Java 7 is my default runtime. Perhaps this is significant?

[Ramesh Pramuditha Rathnayake]

I saw that this class file is created when compiling line 39.

Thread Ping = game.new MyThread(o,true);

As line 39 and 40 are the same, we can think that one class file has replaced..

And when I delete that class file and run the program, no error was given.

I also want an explanation..

[Nikolaos Plastiras]

Paul Clapham wrote:I just compiled it and ran it (in Eclipse) and it completed successfully. And I don't see the PingPong$1.class in the compiled classes folder with the other two.

By the way Java 7 is my default runtime. Perhaps this is significant?

I did that too and got two files in bin folder. But did a classic (1.6) javac compilation and got three files!

[Henry Wong]

Nikolaos Plastiras wrote:

Paul Clapham wrote:I just compiled it and ran it (in Eclipse) and it completed successfully. And I don't see the PingPong$1.class in the compiled classes folder with the other two.

By the way Java 7 is my default runtime. Perhaps this is significant?

I did that too and got two files in bin folder. But did a classic (1.6) javac compilation and got three files!

It works for me too (correctly generated two class files). And yes, I compiled with Java 7.

Henry

[Dan Drillich]

Interesting thing - with jdk 1.7.0_04 I see the three classes -

C:\Program Files\Java\Dan>..\jdk1.7.0_04\bin\javac PingPong.java

....
04/12/2013  07:24 AM               175 PingPong$1.class
04/12/2013  07:24 AM             1,189 PingPong$MyThread.class
04/12/2013  07:24 AM               994 PingPong.class
             111 File(s)         66,460 bytes
               2 Dir(s)  460,211,052,544 bytes free

Regards,
Dan