目录[ Hide ]
  1. 类的加载概述和加载时机
  2. 类加载器的概述和分类
  3. 反射概述
  4. Class.forName()读取配置文件举例
  5. 通过反射获取带参构造方法并使用
  6. 通过反射获取成员变量并使用
  7. 通过反射获取方法并使用
  8. 通过反射越过泛型检查
  9. 通过反射写一个通用的设置某个对象的某个属性为指定的值
  10. 动态代理的概述和实现
  11. Template模板设计模式概述和使用
  12. 自己实现枚举类
  13. 通过enum实现枚举类
  14. 枚举类的常见方法

类的加载概述和加载时机

类加载器的概述和分类

反射概述

Class.forName()读取配置文件举例

package com.heima.reflect;

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

/**
 * Code by pureqh on 2021-03-25
 */
public class Demo2_Reflect {
    public static void main(String[] args) throws Exception {
        /*//未用反射 只在说多态
        Juicer j = new Juicer();    //购买榨汁机
        j.run(new Apple());     //向榨汁机中放入苹果
        j.run(new Orange());    //Fruit f = new Orange();*/
        //用反射和配置文件
        BufferedReader br = new BufferedReader(new FileReader("config.properties"));
        Class clazz = Class.forName(br.readLine());
        Fruit f = (Fruit) clazz.newInstance();  //父类引用指向子类对象
        Juicer j = new Juicer();
        j.run(f);

    }
}
interface  Fruit{
    public void squeeze();
}
class Apple implements Fruit{
    public void squeeze(){
        System.out.println("榨出一杯苹果汁");
    }
}
class Orange implements Fruit{
    public void squeeze(){
        System.out.println("榨出一杯橘子汁");
    }

}
class Juicer{
    /*public void run(Apple a){
        a.squeeze();
    }
    public void run(Orange o){
        o.squeeze();
    }*/
    public void run(Fruit f){
        f.squeeze();
    }
}

config.properties

com.heima.reflect.Apple

通过反射获取带参构造方法并使用

package com.heima.reflect;

import com.heima.bean.Person;

import java.lang.reflect.Constructor;

/**
 * Code by pureqh on 2021-03-26
 */
public class Demo3_Constructor {
    public static void main(String[] args) throws Exception {
        Class clazz = Class.forName("com.heima.bean.Person");
        /*Person p = (Person) clazz.newInstance();  //通过无参构造创建对象
        System.out.println(p);*/
        Constructor c = clazz.getConstructor(String.class,int.class);   //获取有参构造
        Person p = (Person) c.newInstance("张三",23);     //通过有参构造创建对象
        System.out.println(p);

    }
}

通过反射获取成员变量并使用

package com.heima.reflect;

import com.heima.bean.Person;

import java.io.File;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;

/**
 * Code by pureqh on 2021-03-26
 */
public class Demo4_Field {
    public static void main(String[] args) throws Exception {
        Class clazz = Class.forName("com.heima.bean.Person");
        Constructor c = clazz.getConstructor(String.class,int.class);
        Person p = (Person) c.newInstance("张三",23);

        /*Field f = clazz.getField("name");
        f.set(p,"李四");*/
        Field f = clazz.getDeclaredField("name");   //通过暴力反射获取字段
        f.setAccessible(true);
        f.set(p,"李四");
        System.out.println(p);
    }
}

通过反射获取方法并使用

package com.heima.reflect;

import com.heima.bean.Person;

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;

/**
 * Code by pureqh on 2021-03-26
 */
public class Demo5_method {
    public static void main(String[] args) throws Exception {
        Class clazz = Class.forName("com.heima.bean.Person");
        Constructor c = clazz.getConstructor(String.class,int.class);
        Person p = (Person) c.newInstance("张三",23);

        Method m = clazz.getMethod("eat");  //获取eat方法
        m.invoke(p);

        Method m2 = clazz.getMethod("eat",int.class);
        m2.invoke(p, 10);

    }
}

通过反射越过泛型检查

package com.heima.test;
import java.lang.reflect.Method;
import java.util.ArrayList;
/**
 * Code by pureqh on 2021-03-26
 * 泛型只在编译器有效，在运行期会被擦除掉
 */
public class Test1 {
    public static void main(String[] args) throws Exception {
        ArrayList<Integer> list = new ArrayList<>();
        list.add(111);
        Class clazz = Class.forName("java.util.ArrayList"); //获取字节码对象
        Method m = clazz.getMethod("add",Object.class);     //获取add方法
        m.invoke(list,"abc");
        System.out.println(list);
    }
}

通过反射写一个通用的设置某个对象的某个属性为指定的值

package com.heima.test;

import java.lang.reflect.Field;

/**
 * Code by pureqh on 2021-03-26
 */
public class Tool {
    //此方法可以将obj对象中名未propertyName属性的值设置为value
    public void setProperty(Object obj, String property, Object value) throws Exception {
        Class clazz = obj.getClass();   //获取字节码对象
        Field f = clazz.getDeclaredField(property); //暴力反射获取字段
        f.setAccessible(true);
        f.set(obj,value);
    }
}
package com.heima.test;

/**
 * Code by pureqh on 2021-03-26
 */
public class Test3 {
    public static void main(String[] args) throws Exception {
        Student s = new Student("张三",23);
        System.out.println(s);

        Tool t = new Tool();
        t.setProperty(s,"name","李四");
        System.out.println(s);
    }
}
class Student{
    private String name;
    private int age;

    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public Student() {
    }

    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;
    }

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

练习

package com.heima.test;

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;

/**
 * Code by pureqh on 2021-03-26
 */
public class Test2 {
    public static void main(String[] args) throws Exception {
        //创建输入流关联配置文件
        BufferedReader br = new BufferedReader(new FileReader("xxx.properties"));
        Class clazz = Class.forName(br.readLine());     //读取配置文件中的类名，获取字节码对象
        DemoClass dc = (DemoClass) clazz.newInstance();     //通过字节码对象创建对象
        dc.run();


    }
}

xxx.properties

com.heima.test.DemoClass

动态代理的概述和实现

package com.heima.DynamicProxy;

/**
 * Code by pureqh on 2021-03-28
 */
public interface Student {
    public void login();
    public void submit();
}
package com.heima.DynamicProxy;

/**
 * Code by pureqh on 2021-03-28
 */
public class StudentImp implements Student{
    @Override
    public void login() {
        System.out.println("登陆");
    }

    @Override
    public void submit() {
        System.out.println("提交");
    }
}
package com.heima.DynamicProxy;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.net.StandardSocketOptions;

/**
 * Code by pureqh on 2021-03-28
 */
public class MyInvocationHandler implements InvocationHandler {
    private Object target;
    public MyInvocationHandler(Object target){
        this.target = target;
    }
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("权限校验");
        method.invoke(target,args);        //执行被代理target对象的方法
        System.out.println("日志记录");
        return null;
    }
}
package com.heima.DynamicProxy;

import sun.applet.Main;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Proxy;

/**
 * Code by pureqh on 2021-03-28
 */
public class Test {
    public static void main(String[] args) {
        /*UserImp ui = new UserImp();
        ui.add();
        ui.delete();*/
        /**/
        System.out.println("--------------------");
        /*MyInvocationHandler m = new MyInvocationHandler(ui);
        User u = (User) Proxy.newProxyInstance(ui.getClass().getClassLoader(),ui.getClass().getInterfaces(),m);
        u.add();
        u.delete();*/
        StudentImp si = new StudentImp();
        si.login();
        si.submit();
        System.out.println("--------------------");
        MyInvocationHandler m = new MyInvocationHandler(si);
        Student s = (Student) Proxy.newProxyInstance(si.getClass().getClassLoader(),si.getClass().getInterfaces(),m);
        s.login();
        s.submit();
    }
}

Template模板设计模式概述和使用

package com.heima.Template;
/**
 * Code by pureqh on 2021-03-28
 */
public class Demo1_Template {
    public static void main(String[] args) {
        /*long start = System.currentTimeMillis();
        for (int i = 0;i<100;i++){
            System.out.println("*");
        }
        long end = System.currentTimeMillis();
        System.out.println(end - start);*/
        Demo d = new Demo();
        System.out.println(d.getTime());
    }
}
 abstract class GetTime{
    public final long getTime(){
        long start = System.currentTimeMillis();
        code();
        long end = System.currentTimeMillis();
        return end - start;
    }
    public abstract void code();
}
class Demo extends GetTime{
    @Override
    public void code() {
        int i = 0;
        while (i< 10000){
            System.out.println("x");
            i++;
        }
    }
}

自己实现枚举类

package com.heima.enumeration;

/**
 * Code by pureqh on 2021-03-28
 */

public class Week {
    public static final Week MON = new Week();
    public static final Week TUE = new Week();
    public static final Week WED = new Week();
    private Week(){}    //私有构造，不让其他类创建本类对象

}
package com.heima.enumeration;

/**
 * Code by pureqh on 2021-03-28
 */
public class Week2 {
    public static final Week2 MON = new Week2("星期一");
    public static final Week2 TUE = new Week2("星期二");
    public static final Week2 WED = new Week2("星期三");
    private String name;
    private Week2(String name){
        this.name = name;
    }

    public String getName() {
        return name;
    }


}
package com.heima.enumeration;

/**
 * Code by pureqh on 2021-03-28
 */
public abstract class Week3 {
    public static final Week3 MON = new Week3("星期一"){
        public void show(){
            System.out.println("星期一");
        }
    };
    public static final Week3 TUE = new Week3("星期二"){
        public void show(){
            System.out.println("星期二");
        }
    };
    public static final Week3 WED = new Week3("星期三"){
        public void show(){
            System.out.println("星期三");
        }
    };
    private String name;
    private Week3(String name){
        this.name = name;
    }

    public String getName() {
        return name;
    }
    public abstract void show();
}
package com.heima.enumeration;

/**
 * Code by pureqh on 2021-03-28
 */
public class Demo1_Enum {
    public static void main(String[] args) {
        //demo1();
        //demo2();
        Week3 mon = Week3.MON;
        mon.show();

    }

    private static void demo2() {
        Week2 mon = Week2.MON;
        System.out.println(mon.getName());
    }

    private static void demo1() {
        Week mon = Week.MON;
        Week tue = Week.TUE;
        Week wed = Week.WED;
    }
}

通过enum实现枚举类

package com.heima.enumeration2;

/**
 * Code by pureqh on 2021-03-28
 */
public class Demo1_Enum {
    public static void main(String[] args) {
        //demo1();
        //demo2();
        Week3 mon = Week3.MON;
        mon.show();
    }

    private static void demo2() {
        Week2 mon = Week2.MON;
        System.out.println(mon.getName());
    }

    private static void demo1() {
        Week mon = Week.MON;
        System.out.println(mon);
    }
}
package com.heima.enumeration2;

/**
 * Code by pureqh on 2021-03-28
 */
public enum  Week {
    MON,TUE,WED;
}
package com.heima.enumeration2;

/**
 * Code by pureqh on 2021-03-28
 */
public enum  Week2 {
    MON("星期一"),TUE("星期二"),WED("星期三");
    private String name;
    private Week2(String name){
        this.name = name;
    }

    public String getName() {
        return name;
    }
}
package com.heima.enumeration2;

/**
 * Code by pureqh on 2021-03-30
 */
public enum   Week3 {
    MON("星期一") {
        public void show(){
            System.out.println("星期一");
        }
    },TUE("星期二"){
        public void show(){
            System.out.println("星期二");
        }
    },WED("星期三"){
        public void show(){
            System.out.println("星期三");
        }
    };
    private String name;
    private Week3(String name){
        this.name = name;
    }

    public String getName() {
        return name;
    }
    public abstract void show();
}

枚举类的常见方法

package com.heima.enumeration2;

import org.omg.Messaging.SyncScopeHelper;

/**
 * Code by pureqh on 2021-03-30
 */
public class Demo2_Enum {
    public static void main(String[] args) {
        //demo();
/*        Week2 mon = Week2.valueOf(Week2.class,"MON");   //通过字节码对象获取枚举项
        System.out.println(mon);*/
        Week2[] arr = Week2.values();
        for (Week2 week2 :arr
             ) {
            System.out.println(week2);

        }
    }

    private static void demo() {
        Week2 mon = Week2.MON;
        Week2 tue = Week2.TUE;
        Week2 wed = Week2.WED;


        System.out.println(mon.ordinal());  //枚举项都是有编号的
        System.out.println(tue.ordinal());

        System.out.println(mon.compareTo(wed));
        System.out.println(mon.compareTo(tue));

        System.out.println(mon.name());     //获取实例名称
        System.out.println(mon.toString());     //调用重写后的tostring方法
    }


}

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