Exchanger 應用

import java.util.concurrent.Exchanger;

/**
 * 案例：服務員向原有空杯中不斷倒水，消費者不斷從原有裝滿水的杯中喝水。 
 * 當服務員倒滿水和消費者喝完水時，兩個杯子進行交換。一直這樣周而復始。
 * 
 * @author Administrator
 * 
 */
public class TestExchanger {

	static Exchanger<Cup> exchanger = new Exchanger<Cup>();
	static Cup emptyCup = new Cup(0);
	static Cup fullCup = new Cup(100);

	public static void main(String[] args) {
		new Thread(new Waiter(3)).start();
		new Thread(new Customer(6)).start();
	}

	/**
	 * 服務員
	 * 
	 * @author Administrator
	 * 
	 */
	static class Waiter implements Runnable {

		int addSpeed = 1;

		public Waiter(int addSpeed) {
			this.addSpeed = addSpeed;
		}

		@Override
		public void run() {
			while (emptyCup != null) {
				// 若是發現杯子中的水沒有滿，則往杯中加水。
				try {
					if (emptyCup.isFull()) {// 當emptyCup爲裝滿水時而且fullCup爲被喝完水時，進行交換。
						// 當Waiter把杯子水裝滿後，與Customer交換杯子。
						// exchange(emptyCup)中參數的emptyCup是waiter裝滿水後的，把裝滿水後的emptyCup參數傳遞給Cutomer線程。
						// 而且返回Cutomer線程中fullCup給Waiter的emptyCup，這樣就達到了交換效果。
						emptyCup = exchanger.exchange(emptyCup);
						System.out.println("Waiter: " + emptyCup.capacity);
					} else {
						emptyCup.addWaterToCup(3);
						System.out.println("Waiter add " + addSpeed
								+ " and current capacity is "
								+ emptyCup.capacity);
						Thread.sleep((long) (Math
								.max(500, Math.random() * 2000)));
					}
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
		}
	}

	/**
	 * 消費者
	 * 
	 * @author Administrator
	 * 
	 */
	static class Customer implements Runnable {

		int drinkSpeed = 1;

		public Customer(int drinkSpeed) {
			this.drinkSpeed = drinkSpeed;
		}

		@Override
		public void run() {
			while (fullCup != null) {
				// 若是發現杯子中的水沒有滿，則往杯中加水。
				try {
					if (fullCup.isEmpty()) {
						// 水滿後則交換子中的水
						fullCup = exchanger.exchange(fullCup);
						System.out.println("Customer: " + fullCup.capacity);
					} else {
						fullCup.drinkFormCup(drinkSpeed);
						System.out.println("Customer drinked " + drinkSpeed
								+ " and current capacity is "
								+ fullCup.capacity);
						Thread.sleep((long) (Math
								.max(500, Math.random() * 2000)));
					}

				} catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
		}

	}

	static class Cup {

		private int capacity = 0;

		public Cup(int capacity) {
			this.capacity = capacity;
		}

		public void addWaterToCup(int i) {
			capacity += i;
			capacity = capacity > 100 ? 100 : capacity;
		}

		public void drinkFormCup(int i) {
			capacity -= i;
			capacity = capacity < 0 ? 0 : capacity;
		}

		public boolean isFull() {
			return capacity == 100 ? true : false;
		}

		public boolean isEmpty() {
			return capacity == 0 ? true : false;
		}
	}

}