多執行緒之間的通訊，其實就是多個執行緒同時操作（讀+寫）同一個資源。

安全問題：
當執行緒在讀取資源的過程中，寫執行緒操作了資源，
導致讀執行緒讀取的資料，一部分是寫之前的資料，一部分是寫之後的資料。

解決安全問題：
讀執行緒和寫執行緒使用同一把物件鎖就好了。

code of demo：

package cn.qbz.thread;

/**
 * 執行緒間通訊
 */
public class ConnectThreadTest {

    public static void main(String[] args) {
        Student student = new Student
 
();
        ProduceTest produceTest = new ProduceTest(student);
        ConsumerTest consumerTest = new ConsumerTest(student);

        produceTest.start();
        consumerTest.start();

    }
}

class ProduceTest extends Thread {
    private Student student;

    public ProduceTest(Student student)
 
 {
        this.student = student;
    }

    @Override
    public void run() {
        int num = 1;
        while (true) {
            synchronized (student) {
                //如果可以生產，生產者生產
                if (student.getCanProduce()) {
                    if (num == 1) {
                        student.
 
setAge(6);
                        student.setName("小王");
                        num = 0;
                    } else {
                        student.setName("老王");
                        student.setAge(99);
                        num = 1;
                    }

                    //重置生產者不可以生產
                    student.setCanProduce(false);
                }

                student.notifyAll();
                try {
                    student.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

class ConsumerTest extends Thread {
    private Student student;

    public ConsumerTest(Student student) {
        this.student = student;
    }

    @Override
    public void run() {
        while (true) {
            synchronized (student) {
                //如果不可以生產，進行消費
                if (!student.getCanProduce()) {
                    //重置生產者可以生產
                    student.setCanProduce(true);
                    System.out.println(student.toString());
                }

                student.notifyAll();
                try {
                    student.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

class Student {
    private String name;
    private Integer age;
    private Boolean canProduce = false;

    public Boolean getCanProduce() {
        return canProduce;
    }

    public void setCanProduce(Boolean canProduce) {
        this.canProduce = canProduce;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}