反射、注解、线程

反射

反射的定义：

JAVA反射机制是在运行状态中，对于任意一个类，都能够知道这个类的所有属性和方法；对于任意一个对象，都能够调用它的任意一个方法和属性；这种动态获取的信息以及动态调用对象的方法的功能称为java语言的反射机制。
JAVA反射（放射）机制：“程序运行时，允许改变程序结构或变量类型，这种语言称为动态语言”。从这个观点看，Perl，Python，Ruby是动态语言，C++，Java，C#不是动态语言。但是JAVA有着一个非常突出的动态相关机制：Reflection，用在Java身上指的是我们可以在运行时加载、探知、使用编译期间完全未知的classes。换句话说，Java程序可以加载一个运行时才得知名称的class，获悉其完整构造（但不包括methods定义），并生成其对象实体、或对其fields设值、或唤起其methods。

反射实例

.java文件的抽象
Field类中属性的抽象(访问修饰符、属性类型、属性名称)
method类中方法的抽象
Constructor类中构造器的抽象

//Student类中去掉setAge()方法public class Student {public String name;public int age;public String getName() {    return name;}public void setName(String name) {    this.name = name;}public int getAge() {    return age;}public Student(String name,int age){    this.age=age;    this.name=name;}public Student() {}}//******更改年龄***********public static void main(String[] args) {//      Class<Student> stu=Student.class;        System.out.println("***********************************");//      Student zhangsan=new Student();//      Class<Student> stu= (Class<Student>) zhangsan.getClass();        System.out.println("************************************");//      Student zhangsan=new Student();//      try {//          Class<Student> clazz=(Class<Student>) Class.forName("com.lingzhuo.test.Student");//      } catch (ClassNotFoundException e) {//          // TODO Auto-generated catch block//          e.printStackTrace();//      }        System.out.println("*************************************");        Student zhangsan=new Student();        //反射     Class<Student> clazz=Student.class;     //得到student.Java的Class的抽象     try {        Field field=clazz.getDeclaredField("age");//得到某一个(age的)属性        field.setAccessible(true);//去掉访问修饰符        field.set(zhangsan, 31);//更改它的值        field.setAccessible(false);//在将访问修饰符改成false    } catch (NoSuchFieldException | SecurityException e) {        // TODO Auto-generated catch block        e.printStackTrace();    } catch (IllegalArgumentException e) {        // TODO Auto-generated catch block        e.printStackTrace();    } catch (IllegalAccessException e) {        // TODO Auto-generated catch block        e.printStackTrace();    }    System.out.println(zhangsan.getAge());    }}

注解

Annotation

注解范例（1）

//**************先生成一个注解****************@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.FIELD)public @interface StudentAnnotation {    // 运行范围 一个类似注释不会编译 一个是会进行代码检查 一种是 运行时的注解    // 注解类型 给class注解一个给field注解 一个给method注解    // 一个给Constructor注解    // 可以传入值    String name();//*****************在创建一个类************public class Student {    // 给name加一个注解    @StudentAnnotation(name = "张三")    private String name;    private int age;    public Student() {        Class<Student> clazz = Student.class;        try {            Field fieldName = clazz.getDeclaredField("name");// 找到name属性            StudentAnnotation anno = fieldName.getAnnotation(StudentAnnotation.class);            String name = anno.name();//           fieldName.setAccessible(true);             fieldName.set(this, name);//           fieldName.setAccessible(false);        } catch (NoSuchFieldException | SecurityException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (IllegalArgumentException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (IllegalAccessException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public int getAge() {        return age;    }    public Student(String name, int age) {        this.age = age;        this.name = name;    }}//***********测试****************public class Test {    public static void main(String[] args) {        Student stu = new Student();        System.out.println(stu.getName());    }}

注解范例（2）

"生成一个TeacherAnnotation"@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.FIELD)public @interface TeacherAnnotation { int age() default 19; String name();}"一个Teacher类"public class Teacher {private String name;private int age;public String getName() {    return name;}public void setName(String name) {    this.name = name;}public int getAge() {    return age;}public void setAge(int age) {    this.age = age;}}"一个Clazz类"public class Clazz {    @TeacherAnnotation(age = 20, name = "张三")    private Teacher javaTeacher;    @TeacherAnnotation(age = 21, name = "李四")    private Teacher englishTeacher;    @TeacherAnnotation(age = 22, name = "王五")    private Teacher mathTeacher;    private int age;    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    public Clazz() {        Class<Clazz> clazz = Clazz.class;        Field[] fields = clazz.getDeclaredFields();        for (Field field : fields) {            TeacherAnnotation ta = field.getAnnotation(TeacherAnnotation.class);            if (ta == null) {                continue;            } else {                int age = ta.age();                String name = ta.name();                Teacher teacher = new Teacher();                teacher.setName(name);                teacher.setAge(age);//              field.setAccessible(true);                try {                    field.set(this, teacher);                } catch (IllegalArgumentException e) {                    // TODO Auto-generated catch block                    e.printStackTrace();                } catch (IllegalAccessException e) {                    // TODO Auto-generated catch block                    e.printStackTrace();                }//              field.setAccessible(false);            }        }    }    public Teacher getJavaTeacher() {        return javaTeacher;    }    public void setJavaTeacher(Teacher javaTeacher) {        this.javaTeacher = javaTeacher;    }    public Teacher getEnglishTeacher() {        return englishTeacher;    }    public void setEnglishTeacher(Teacher englishTeacher) {        this.englishTeacher = englishTeacher;    }    public Teacher getMathTeacher() {        return mathTeacher;    }    public void setMathTeacher(Teacher mathTeacher) {        this.mathTeacher = mathTeacher;    }}"测试类"public static void main(String[] args) {        Clazz clazz=new Clazz();        System.out.println( clazz.getEnglishTeacher().getName());        System.out.println(clazz.getMathTeacher().getAge());    }

线程

线程实现的两种方式：

一种是继承Thread类，一种是实现Runnable接口，Runnable的优点是能实现数据共享。

注意：

必须重写run方法，必须调用start方法才是启动线程

线程的休眠 ( sleep) 休眠多少秒后唤醒
线程的优先级1-10
线程锁：

同一时间只能有一个线程访问该同步代码块

卖票(线程锁)

public class MyRunnable implements Runnable {    private int cards = 1000;    private String lock = "abc";    @Override    public void run() {        while (cards > 0) {            synchronized (lock) {                if (cards > 0) {                    System.out.println("我是线程" + Thread.currentThread().getName()+"我卖的票号"+cards);                    cards--;                }            }        }    }}"***************测试类****************"MyRunnable run=new MyRunnable();    Thread t1=new Thread(run);    Thread t2=new Thread(run);    Thread t3=new Thread(run);    t1.start();    t2.start();    t3.start();

同步方法

线程间通讯 wait释放此线程 notify唤醒等待的线程
线程生命周期
线程创建 线程的新生（调用start的方法）
休眠sleep 阻塞wait 唤醒notify
线程死亡

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卖票(同步方法)

//*****************建立一个WanDa类***************public class WanDa {    private int tickets = 1000;    public synchronized void sell() {        if (tickets > 0) {            System.out.println(Thread.currentThread().getName() + "我卖的票号" + tickets);            tickets--;        }    }    public void sellAll(){        while(tickets>0){            sell();        }    }}//*************建立一个MyRunnable类***************public class MyRunnable implements Runnable{    private WanDa wd;    public MyRunnable(WanDa wd){        this.wd=wd;    }    @Override    public void run() {    wd.sellAll();    }}//***************测试类*****************public static void main(String[] args) {    WanDa wd=new WanDa();    MyRunnable run=new MyRunnable(wd);    Thread t1=new Thread(run);    Thread t2=new Thread(run);    Thread t3=new Thread(run);    t1.start();    t2.start();    t3.start();}

生产者与消费者

仓库 消费者 生产者 消费者查看仓库，如果有产品会消费产品，如果没有产品通知生产者生产者生产产品。生产者查看仓库，有就通知消费者消费产品，无则生产。

//****************消费者**************public class Consumer extends Thread {    private Product pro;    public Consumer(Product pro){        this.pro=pro;    }@Overridepublic void run() {    while(true){    synchronized (pro) {        if(pro.getNum()>0){            System.out.println("消费产品");            pro.setNum(0);            work(1000);            pro.notify();        }else{            System.out.println("等待生产者生产");            try {                pro.wait();            } catch (InterruptedException e) {                // TODO Auto-generated catch block                e.printStackTrace();            }            work(1000);        }    }    }    }    public void work(long time){        try {            sleep(time);        } catch (InterruptedException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }}}//********************生产者**********************public class Producer extends Thread{private Product pro;public Producer(Product pro){    this.pro=pro;}@Override    public void run() {    while(true){        synchronized (pro) {            if(pro.getNum()>0){                System.out.println("等待消费者消费");                work(1000);                try {                    pro.wait();                } catch (InterruptedException e) {                    // TODO Auto-generated catch block                    e.printStackTrace();                }            }else{                System.out.println("生产者生产");                work(1000);                pro.setNum(1);                pro.notify();            }        }    }    }public void work(long time){    try {        sleep(time);    } catch (InterruptedException e) {        // TODO Auto-generated catch block        e.printStackTrace();    }}}//******************仓库(产品)**********************public class Product {private int num=1;public int getNum() {    return num;}public void setNum(int num) {    this.num = num;}}//***********************测试类*************ublic static void main(String[] args) {    Product pro=new Product();    Producer producer=new Producer(pro);    Consumer consumer=new Consumer(pro);    producer.start();    consumer.start();}