JAVA基础一大堆0804反射+注解

反射

例1

public class Person {    public  void sleep(){        System.out.println("人睡觉");    }}public class Student extends Person{    @Override    public void sleep() {    System.out.println("学生睡觉");    }}public class Teacher extends Person{    @Override    public void sleep() {        System.out.println("老师睡觉");    }}public class Worker extends Person{    @Override    public void sleep() {        System.out.println("工人睡觉");    }}import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.IOException;import java.util.Properties;public class Factory {    public static Person creatPerson(){        Person person=null;                     //定义要返回的变量        Properties p=new Properties();          //创建一个带有指定默认值的空属性列表        try {            p.load(new FileInputStream("config.properties"));//从输入流中读取属性列表（键和元素对).            String clazzName=p.getProperty("vocation");//用指定的键在此属性列表中搜索属性            Class clazz=Class.forName(clazzName);//返回与带有给定字符串名的类或接口相关联的 Class 对象            person=(Person) clazz.newInstance();//newInstance创建此 Class 对象所表示的类的一个新实例        } catch (FileNotFoundException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        } catch (ClassNotFoundException e) {            e.printStackTrace();        } catch (InstantiationException e) {            e.printStackTrace();        } catch (IllegalAccessException e) {            e.printStackTrace();        }        return person;    }}public class FactoryTest {    public static void main(String[] args) {        Person person=Factory.creatPerson();        person.sleep();    }}

config.properties文件：vocation=com.lingzhuo.reflect.Teacher

config.properties文件：vocation=com.lingzhuo.reflect.Worker

例2

public class Student {    private int age;    public String name;    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public int getAge() {        return age;    }}import java.lang.reflect.Field;public class RelfectTest {    public static void main(String[] args) {        Class<Student> clazz=Student.class;//就是由已有的类产生他的抽象类，Class<Student>即Student的抽象类//      Field[] fields=clazz.getFields();//以数组形式返回所有公共属性，注意是公共属性（public）        Field[] fields=clazz.getDeclaredFields();//以数组形式返回所有的属性        for (Field field : fields) {            System.out.println(field.getName());//返回的属性名称            System.out.println(field.getType().getName());//返回属性的类型名称            System.out.println(field.getModifiers());//返回属性修饰符的整数表示形势        }        Student zhangsan=new Student();        try {            Field age = clazz.getDeclaredField("age");//得到指定名称的属性age            age.setAccessible(true);                //取消java访问修饰符检查            age.set(zhangsan, 18);                  //将对象zhangsan的age属性值更改为18            age.setAccessible(false);               //恢复检查            System.out.println(zhangsan.getAge());  //输出age值        } catch (NoSuchFieldException e) {            e.printStackTrace();        } catch (SecurityException e) {            e.printStackTrace();        } catch (IllegalArgumentException e) {            e.printStackTrace();        } catch (IllegalAccessException e) {            e.printStackTrace();        }           }}

注解

例1

import java.lang.reflect.Field;public class Student {    @StudentAnnotation(18)    private int age;    public Student(){        //反射        Class clazz=Student.class;//得到student类的Class的对象        try {            Field field=clazz.getDeclaredField("age");//得到age属性            StudentAnnotation sa=field.getAnnotation(StudentAnnotation.class);            //得到age属性的StudentAnnotation注解，如果没有返回null            if(sa!=null){                int i=sa.value();//获得属性的默认值                field.setAccessible(true);//设置为不检查属性的访问修饰符                field.set(this, i);//this指的是Student的对象                //将Student的对象的age属性修改为i                field.setAccessible(false);//设置属性的访问修饰符检查            }        } catch (NoSuchFieldException e) {            e.printStackTrace();        } catch (SecurityException e) {            e.printStackTrace();        } catch (IllegalArgumentException e) {            e.printStackTrace();        } catch (IllegalAccessException e) {            e.printStackTrace();        }    }    public String clazz;    public String name;    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public int getAge() {        return age;    }}import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;@Retention(RetentionPolicy.RUNTIME)//此范围内的注解可以执行@Target(ElementType.FIELD)//表示此注解只能用到属性上public @interface StudentAnnotation {    int value();//表明此注解可以注解一个int值}public class Test {    public static void main(String[] args) {        Student zhangsan=new Student();        System.out.println(zhangsan.getAge());    }}

例2

import java.lang.reflect.Field;public class Clazz {    @TeacherAnnotation(age=20,name="张三")    private Teacher javaTeacher;    @TeacherAnnotation(age=22,name="李四")    private Teacher englishTeacher;    @TeacherAnnotation(name="王五")    private Teacher mathTeacher;    private int clazzNum;    private String name;    public Clazz(){        Class clazz=Clazz.class;        Field[] fields=clazz.getDeclaredFields();        //得到clazz所有的属性        for(Field field:fields){            TeacherAnnotation ta=field.getAnnotation(TeacherAnnotation.class);            //得到TeacherAnnotation注解，如果没有返回null            if(ta==null){                continue;//如果为null跳出            }else{                int age=ta.age();//得到该注解的age值，如果没有使用默认值                String name=ta.name();//得到该注解的name值                Teacher teacher=new Teacher();                teacher.setAge(age);                teacher.setName(name);//根据注解的值创建新的对象                field.setAccessible(true);//设置为不检查属性的访问修饰符                try {                    field.set(this,teacher);//将这个teacher对象赋值给此班级对象的该属性                } catch (IllegalArgumentException e) {                    e.printStackTrace();                } catch (IllegalAccessException e) {                    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;    }    public int getClazzNum() {        return clazzNum;    }    public void setClazzNum(int clazzNum) {        this.clazzNum = clazzNum;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }}public class Teacher {    private int age;    private String name;    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }}import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.FIELD)public @interface TeacherAnnotation {    int age() default 19;//如果age在注解中没有声明则使用默认default值    String name();}public class Test {    public static void main(String[] args) {        Clazz clazz=new Clazz();        System.out.println(clazz.getEnglishTeacher().getName()+clazz.getEnglishTeacher().getAge());        System.out.println(clazz.getMathTeacher().getName()+clazz.getMathTeacher().getAge());    }}