Java使用反射操作类构造器

使用反射操作分别利用public无参构造器、public有参构造器、private有参构造器创建对象实例。

其中，private有参构造器创建实例需要使用暴破操作

package test;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;


public class Test {
    public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException, NoSuchMethodException, InvocationTargetException {
        //1.先获取Person类的Class对象
        Class personClass = Class.forName("test.Person");
        //方法1：通过public的无参构造器创建实例
        Object person1 = personClass.newInstance();
        System.out.println(person1);

        //方法2：通过public的有参构造器创建实例
        Constructor constructor = personClass.getConstructor(String.class);
        
        Object person2 = constructor.newInstance("john");
        System.out.println(person2);

        //方法3：通过非public的有参构造器创建实例
        Constructor declaredConstructor = personClass.getDeclaredConstructor(String.class, int.class);//得到private的构造器对象
        declaredConstructor.setAccessible(true);//暴破，使用反射可以访问private构造器/方法/属性
        Object person3 = declaredConstructor.newInstance("mike", 30);
        System.out.println(person3);

    }
}

class Person {
    private String name;
    private int age;

    public Person() {
    }

    public Person(String name) {
        this.name = name;
    }

    private Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

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