Java反射机制调用private类型的构造方法

package singleton;

public class SingletonTest {

    // 私有构造方法
    private SingletonTest(){
        
        System.out.println("无参数---构造----");  
    }
    // 私有构造方法
    private SingletonTest(String a){
        
        System.out.println("有参数---构造----参数值：" + a);  
    }
    //定义私有类型的变量
    private static volatile  SingletonTest instance;
    
    //定义一个静态共有方法
    public static SingletonTest getInstance(){
        
        if(instance == null){
            synchronized(SingletonTest.class){
                if(instance == null){
                    return new SingletonTest();
                }
            }
        }
        return instance;
    }
}

package reflect;

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

import singleton.SingletonTest;

public class ReflectDemo {

    public static void main(String[] args) throws Exception{
        Class clazz = SingletonTest.class;

        /*以下调用无参的、私有构造函数*/   
        Constructor c0=  clazz.getDeclaredConstructor();   
        c0.setAccessible(true); 
        SingletonTest po=(SingletonTest)c0.newInstance();   
        System.out.println("无参构造函数\t"+po); 

        /*以下调用带参的、私有构造函数*/   
        Constructor c1=clazz.getDeclaredConstructor(new Class[]{String.class});   
        c1.setAccessible(true);   
        SingletonTest p1=(SingletonTest)c1.newInstance(new Object[]{"我是参数值"});   
        System.out.println("有参的构造函数\t"+p1);  

    }

}