https://blog.csdn.net/jiahao1186/article/details/81699582

In reflection, to obtain a Class or call a method of a Class, first obtain the Class object of the Class.

1. Get Class object

In the Java API, there are three methods to obtain Class objects:

First, use the Class.forName static method.

Premise: the full pathname of the class has been specified.

Second, use the. class method.

Note: only applicable to classes that have been explicitly operated before Compilation

Third, use the getClass() method of the class object.

Suitable when there are object examples

Code example:

package com.reflection;
 
/**
 * Created by Liuxd on 2018-08-15.
 */
public class User {
    private String name;
    private Integer age;
 
    public User() {
    }
 
    public User(String name, Integer age) {
        this.name = name;
        this.age = age;
    }
 
    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 "User{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

package com.reflection;
 
/**
 * Created by Liuxd on 2018-08-15.
 */
public class TestReflection {
 
    public static void main(String[] args) {
//      First, Class.forName
        Class clazz1 = null;
        try {
            clazz1 = Class.forName("com.reflection.User");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
 
//      Second, get the object through the object instance method
        Class clazz2 = User.class;
 
//      Third, through the getClass method of the Object class
        User user = new User();
        Class clazz3 = user.getClass();
 
        System.out.println(clazz1);
        System.out.println(clazz2);
        System.out.println(clazz3);
    }
}

2. Get object instance

There are two methods:

2.1. Obtain the corresponding instance directly with bytecode file

// Call the parameterless constructor. If not, an exception will be reported.

Object o = clazz.newInstance();　　

2.2 for a class with a constructor with parameters, first obtain its construction object, and then obtain an instance through the construction method class:

/ /Get object of constructor class
Constroctor constroctor = clazz.getConstructor(String.class,Integer.class); /
// Initializing an object using the newInstance method of the constructor object
Object obj = constroctor.newInstance("Long Ge", 29); 

Code example:

package com.reflection;
 
import java.lang.reflect.Constructor;
 
/**
 * Created by Liuxd on 2018-08-15.
 */
public class TestReflection {
 
    public static void main(String[] args) {
//      First, Class.forName
        Class clazz1 = null;
        try {
            clazz1 = Class.forName("com.reflection.User");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
 
//      Second, get the object through the object instance method
        Class clazz2 = User.class;
 
//      Third, through the getClass method of the Object class
        User user = new User();
        Class clazz3 = user.getClass();
 
        System.out.println(clazz1);
        System.out.println(clazz2);
        System.out.println(clazz3);
 
        User user1 = null;
        try {
             user1 =(User) clazz1.newInstance();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
        user1.setName("Terminator");
        user1.setAge(1500);
        System.out.println("user1:"+user1.toString());
 
 
        User user2 = null;
        try {
            // Get constructor
            Constructor constroctor = clazz2.getConstructor(String.class,Integer.class);
            // Initializing an object through the newInstance method of the constructor object
            user2 = (User) constroctor.newInstance("Long Ge",29);
        } catch (Exception e) {
            e.printStackTrace();
        }
        System.out.println("user2:"+user2.toString());

    }
}