Dúvidas com Threads

public class Teste {

	static class Task1 implements Runnable {

		private int id;

		public Task1(int id) {
			this.id = id;
		}

		public void run() {
			// executa 3 threads, cada uma executa a Task2.
			Thread th1 = new Thread(new Task2(id, 1));
			Thread th2 = new Thread(new Task2(id, 2));
			Thread th3 = new Thread(new Task2(id, 3));
			th1.start();
			th2.start();
			th3.start();
		}

	}

	static class Task2 implements Runnable {

		private int id1;

		private int id2;

		public Task2(int id1, int id2) {
			this.id1 = id1;
			this.id2 = id2;
		}

		public void run() {
			// faz algo
			try {
				Thread.sleep(Double.valueOf(Math.random() * 300).longValue());
			} catch (InterruptedException e) {
			}
			System.out.println("thread principal: " + id1 + " filha: " + id2);
		}

	}

	public static void main(String[] args) {
		// executa 3 threads, cada uma executa a Task1 que por sua vez executa
		// mais 3
		Thread tp1 = new Thread(new Task1(1));
		Thread tp2 = new Thread(new Task1(2));
		Thread tp3 = new Thread(new Task1(3));

		tp1.start();
		tp2.start();
		tp3.start();
	}

}