多线程

有2中方法可以来创建线程：

• 继承Thread类
• 用一个类实现Runnable接口
  具体如下:

package com.qingke.thread;

public class LeannThread {
    public static void main(String[] args) {
        Thread code = new Code();
        code.setName("编写");
        Print print = new Print();
        Thread pr = new Thread(print, "打印机");
        code.start();
        pr.start();
    }

}

class Code extends Thread {
    public void run() {
        for (int i = 1; i <= 100; i++) {
            System.out.println(this.getName() + ":" + "小明在写第" + i + "行代码");

            try {
                Thread.sleep(10);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        System.out.println("代码写完！");

    }
}

class Print implements Runnable {

    @Override
    public void run() {
        for (int i = 1; i <= 15; i++) {
            System.out.println(Thread.currentThread().getName() + ":" + "小明在打印第" + i + "页材料");

            try {
                Thread.sleep(10);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        System.out.println("打印完！");
    }

}

在对于像银行账户的需要同步的问题上，现在有一个例子：
一对夫妻在银行有一个共同的账户，则需要用到同步使得账户中的余额保持同步。
如下：

package com.qingke.thread;

public class BankThread {
    public static void main(String[] args) {
        BankAccount count = new BankAccount();
        Thread husband = new BankedThread(count);
        Thread wife = new BankedThread(count);
        husband.start();
        wife.start();
    }

}

class BankAccount {
    private double balance = 1000;

    public /*synchronized*/boolean deposit(double newAdd) {
        if (balance <= 0) {
            return false;
        } else {
            synchronized (this) {
                System.out.println("当前余额为" + balance);

                balance += newAdd;

                System.out.println("当前余额为" + balance);
            }
            return true;
        }
    }
}

class BankedThread extends Thread {
    private BankAccount bankAccount;

    public BankedThread(BankAccount count) {
        bankAccount = count;
    }

    public void run() {
        bankAccount.deposit(200);
    }
}

在上述代码中synchronized 可以直接放在方法声明上，也可以写在方法块内synchronized（obj）{} * ** obj*表示需要同步的对象。

---

模拟一种场景，假设有一个生产商Producer和一个消费者Consumer，另外有一个容器Box，Box中只能放一样东西。若Box为空，则要等Producer生产出来再放到Box中，在通知Consumer。若Box中不空，则需要等Consumer拿完，在通知Producer。
代码如下：

package com.qingke.thread;

public class LearnThreadCommunication {
    public static void main(String[] args) {
        Box box = new Box();
        Thread producer = new Producer(box);
        Thread consumer = new Consumer(box);
        producer.start();
        consumer.start();

    }
}

class Box {
    public int boxValue = 0;
}

class Producer extends Thread {
    private Box box;

    public Producer(Box box) {
        this.box = box;
    }

    public void run() {
        for (int i = 1; i < 6; i++) {

            synchronized (box) {
                while (box.boxValue != 0) {
                    try {
                        System.out.println("Producer: Box是满的，等待");
                        box.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                box.boxValue = i;
                System.out.println("Producer: Box中放入了" + i + ",并通知其他等待者");
                box.notify();
            }
        }
    }
}

class Consumer extends Thread {
    private Box box;

    public Consumer(Box box) {
        this.box = box;
    }

    public void run() {
        for (int i = 1; i < 6; i++) {

            synchronized (box) {
                while (box.boxValue == 0) {
                    try {
                        System.out.println("Consumer: Box是空的，等待");
                        box.wait();
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
                box.boxValue = 0;
                System.out.println("Consumer: Box中取出了" + i + ",并通知供应者");
                box.notify();
            }
        }
    }
}

用到Object的 wait()和notify()方法