类加载和反射

转载

mb5fed701509fd9 2021-07-23 21:24:00

文章标签 java 构造方法 d3 ide 成员变量 文章分类 代码人生

类加载

package com.ding;

import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

/**
 * @Description TODO
 * @Author 丁帅帅
 * @Date 21/07/23 10:39
 * @Version 1.0
 */
public class ClassLoaderDemo {

    public static void main(String[] args) throws IOException {

        //获取系统类加载器
        ClassLoader systemClassLoader = ClassLoader.getSystemClassLoader();

        /**
         * 利用加载器去加载一个指定文件
         * 参数:文件路径
         * 返回值:字节流
         */
        InputStream is = systemClassLoader.getResourceAsStream("prop.properties");

        Properties prop = new Properties();
        prop.load(is);

        System.out.println(prop);
        is.close();
    }
}

name=zhangsan
age=13
sex=nan

反射

1.结构图

reflect1

className=com.ding.reflect1.Student
methodName=study

package com.ding.reflect1;

import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Properties;

/**
 * @Description TODO
 * @Author 丁帅帅
 * @Date 21/07/23 11:07
 * @Version 1.0
 */
public class ReflectDemo1 {

    public static void main(String[] args) throws IOException, ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {

        InputStream is = ClassLoader.getSystemClassLoader().getResourceAsStream("prop.properties");

        //创建Properties集合
        Properties properties = new Properties();
        //将文件中的数据读取到集合当中
        properties.load(is);

        is.close();


        //利用反射创建对象并调用方法

        //获取字节码文件对象
        Class<?> clazz = Class.forName(properties.getProperty("className"));
        //获取构造器对象
        Constructor constructor = clazz.getConstructor();

        //利用构造器对象创建一个对象
        Object o = constructor.newInstance();

        //获取方法对象
        Method method = clazz.getMethod(properties.getProperty("methodName"));

        //运行方法
        method.invoke(o);
    }

}

package com.ding.reflect1;

/**
 * @Description TODO
 * @Author 丁帅帅
 * @Date 21/07/23 11:26
 * @Version 1.0
 */

public class Student {

    private String name;
    private int age;

    public Student() {
    }

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

    public void study(){
        System.out.println("学生在学习");
    }

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

package com.ding.reflect1;

/**
 * @Description TODO
 * @Author 丁帅帅
 * @Date 21/07/23 11:27
 * @Version 1.0
 */
public class Teacher {
    private String name;
    private int age;

    public Teacher() {
    }

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

    public void teach(){
        System.out.println("老师在上课");
    }

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

package com.ding.reflect1;

/**
 * @Description TODO
 * @Author 丁帅帅
 * @Date 21/07/23 11:27
 * @Version 1.0
 */


public class Worker {
    private String name;
    private int age;

    public Worker() {
    }

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

    public void work(){
        System.out.println("工人在工作");
    }

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

reflect2(获取class对象的三种方式)

package com.ding.reflect2;

/**
 * @Description TODO
 * @Author 丁帅帅
 * @Date 21/07/23 11:26
 * @Version 1.0
 */

public class Student {

    private String name;
    private int age;

    public Student() {
    }

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

    public void study(){
        System.out.println("学生在学习");
    }

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

package com.ding.reflect2;

/**
 * @Description 获取class对象的三种方式
 * @Author 丁帅帅
 * @Date 21/07/23 11:38
 * @Version 1.0
 */
public class ReflectDemo {

    public static void main(String[] args) throws Exception {
        //1.Class类中的静态方法forName("全类名)
        //全类名=包名+类名
        Class clazz = Class.forName("com.ding.reflect2.Student");

        System.out.println(clazz);


        //2.通过class属性来获取
        Class<Student> clazz2 = Student.class;
        System.out.println(clazz2);

        //3.通过对象的getClass方法来获取class对象
        //getClass方法是定义在Object类中
        Student student = new Student();

        Class clazz3 = student.getClass();
        System.out.println(clazz3);


        System.out.println(clazz == clazz2);
        System.out.println(clazz2 == clazz3);
    }
}

reflect3(获取1Constructor对象并创建对象)

package com.ding.reflect3;

/**
 * @Description TODO
 * @Author 丁帅帅
 * @Date 21/07/23 16:22
 * @Version 1.0
 */
public class Student {
    private String name;
    private int age;


    //私有的有参构造方法
    private Student(String name){
        System.out.println("name的值为:"+name);
        System.out.println("private ..Student..有参构造方法");
    }
    //公共的无参构造方法
    public Student() {
        System.out.println("public...Student...无参构造方法");
    }

    //公共的有参构造方法
    public Student(String name, int age) {
        System.out.println("name的值为:" + name + "age的值为:" + age);
        System.out.println("public...Student...有参构造方法");
    }

}

package com.ding.reflect3;

import java.lang.reflect.Constructor;

/**
 * @Description 获取Constructor对象
 * @Author 丁帅帅
 * @Date 21/07/23 16:26
 * @Version 1.0
 */
public class ReflectDemo1 {

    public static void main(String[] args) throws  Exception{
       // method1();
        //method2();
        //method3();
        //返回单个构造方法对象
        Class clazz = Class.forName("com.ding.reflect3.Student");
        Constructor constructor = clazz.getDeclaredConstructor(String.class);
        System.out.println(constructor);


    }

    private static void method3() throws ClassNotFoundException, NoSuchMethodException {
        // 返回单个公共构造方法对象
        Class clazz = Class.forName("com.ding.reflect3.Student");
        Constructor constructor1 = clazz.getConstructor();
        System.out.println(constructor1);

        Constructor constructor2 = clazz.getConstructor(String.class, int.class);
        System.out.println(constructor2);
    }

    private static void method2() throws ClassNotFoundException {
        //返回所有构造方法对象的数组
        Class clazz = Class.forName("com.ding.reflect3.Student");
        Constructor[] constructors = clazz.getDeclaredConstructors();
        for (Constructor constructor : constructors) {
            System.out.println(constructor);
        }
    }

    private static void method1() throws ClassNotFoundException {
        //  返回所有公共构造方法对象的数组
        Class clazz = Class.forName("com.ding.reflect3.Student");
        Constructor[] constructors = clazz.getConstructors();
        for (Constructor constructor : constructors) {
            System.out.println(constructor);
        }
    }
}

package com.ding.reflect3;

import java.lang.reflect.Constructor;

/**
 * @Description 获取1Constructor对象并创建对象
 * @Author 丁帅帅
 * @Date 21/07/23 16:45
 * @Version 1.0
 */
public class ReflectDemo2 {

    public static void main(String[] args) throws Exception {
       // method1();
        //method2();
        //method3();

    }

    private static void method3() throws ClassNotFoundException, NoSuchMethodException, InstantiationException, IllegalAccessException, java.lang.reflect.InvocationTargetException {
        //获取一个私有的构造方法并创建对象
        Class<?> clazz = Class.forName("com.ding.reflect3.Student");
        Constructor<?> constructor = clazz.getDeclaredConstructor(String.class);

        //被private修饰的成员,不能直接使用
        //如果用反射强行获取并使用,需要临时取消访问检查
        constructor.setAccessible(true);

        Student stu = (Student) constructor.newInstance("lisi");

        System.out.println(stu);
    }

    private static void method2() throws ClassNotFoundException, NoSuchMethodException, InstantiationException, IllegalAccessException, java.lang.reflect.InvocationTargetException {
        Class<?> clazz = Class.forName("com.ding.reflect3.Student");

        Constructor<?> constructor = clazz.getConstructor();

        Student stu = (Student) constructor.newInstance();

        System.out.println(stu);
    }


    private static void method1() throws ClassNotFoundException, NoSuchMethodException, InstantiationException, IllegalAccessException, java.lang.reflect.InvocationTargetException {
        //1.获取class对象
        Class<?> clazz = Class.forName("com.ding.reflect3.Student");

        //2.获取构造方法对象
        Constructor<?> constructor = clazz.getConstructor(String.class, int.class);

        //3.利用newInstance创建Student对象
        Student student = (Student) constructor.newInstance("zhangsan", 23);

        System.out.println(student);
    }
}

reflect4(获取Field对象)

package com.ding.reflect4;

/**
 * @Description TODO
 * @Author 丁帅帅
 * @Date 21/07/23 16:43
 * @Version 1.0
 */
public class Student {

    public String name;

    public int age;

    public String gender;

    private int money = 300;


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

package com.ding.reflect4;

import java.lang.reflect.Field;

/**
 * @Description 获取Field对象
 * @Author 丁帅帅
 * @Date 21/07/23 17:01
 * @Version 1.0
 */
public class ReflectDemo1 {

    public static void main(String[] args) throws Exception {
       // method1();
        //method2();
        //method3();
        //返回单个成员变量对象
        Class<?> clazz = Class.forName("com.ding.reflect4.Student");
        Field money = clazz.getDeclaredField("money");

        System.out.println(money);
    }

    private static void method3() throws ClassNotFoundException, NoSuchFieldException {
        //返回单个公共成员变量对象
        Class<?> clazz = Class.forName("com.ding.reflect4.Student");
        Field name = clazz.getField("name");
        System.out.println(name.getName());
    }

    private static void method2() throws ClassNotFoundException {
        //返回所有成员变量对象的数组
        Class<?> clazz = Class.forName("com.ding.reflect4.Student");
        Field[] fields = clazz.getDeclaredFields();
        for (Field field : fields) {
            System.out.println(field);
        }
    }

    private static void method1() throws ClassNotFoundException {
        //Field[] getFields()：返回所有公共成员变量对象的数组
        Class<?> clazz = Class.forName("com.ding.reflect4.Student");

        Field[] field = clazz.getFields();

        for (Field field1 : field) {
            System.out.println(field1);
        }
    }


}

package com.ding.reflect4;

import java.lang.reflect.Field;

/**
 * @Description 利用Field对象,获取值或者修改值
 * @Author 丁帅帅
 * @Date 21/07/23 17:12
 * @Version 1.0
 */
public class ReflectDemo2 {

    public static void main(String[] args) throws  Exception{
       // method1();
        Class<?> clazz = Class.forName("com.ding.reflect4.Student");
        Field field = clazz.getDeclaredField("money");
        field.setAccessible(true);
        Student stu = (Student) clazz.newInstance();
        Object o = field.get(stu);
        field.set(stu,400);
        System.out.println(o);
        System.out.println(stu);

    }

    private static void method1() throws ClassNotFoundException, NoSuchFieldException, InstantiationException, IllegalAccessException {
        //给obj对象的成员变量赋值为value
        //1.获取class对象
        Class<?> clazz = Class.forName("com.ding.reflect4.Student");
        //2.获取name这个Field对象
        Field field = clazz.getField("name");

        //3.利用set方法进行赋值
        //3.1先创建一个Student对象
        Student stu = (Student) clazz.newInstance();
        //3.2对指定对象进行赋值
        field.set(stu,"ding");
        System.out.println(stu);
    }
}

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