class Person{
    private String name ;
    private String sex ;
    public  Person(){
        System.out.println("c");
    }
    public  Person(String c1){
         this.name =c1;
        System.out.println("c1"+c1);
    }
    public  Person(String c1,String c2){
        this.name =c1;
        this
 
.sex =c2;
        System.out.println("c1"+c1 +"c2"+c2);
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }


}    
 

 public  static  void  main(String [] args){
        try {
            Class<?> clazz = Class.forName("com.leeeason.miaosha.Person") ; // 取得Class對象
            Constructor<?>[] constructors = clazz.getConstructors();
            System.out.print(constructors.length);
            Object o 
 
= constructors[0].newInstance();
        } catch (Exception e) {
            e.printStackTrace();
        }

    }

報錯java.lang.IllegalArgumentException: wrong number of arguments

因為構造函數取值的時候是從下往上 從0開始

  public  static  void  main(String [] args){
        try {
            Class<?> clazz = Class.forName("com.leeeason.miaosha.Person") ; // 取得Class對象
            Constructor<?>[] constructors = clazz.getConstructors();
            //System.out.print(constructors.length);
            //修改後
            Object o = constructors[2].newInstance();
        } catch (Exception e) {
            e.printStackTrace();
        }

    }

返回成功

反射報錯java.lang.IllegalArgumentException: wrong number of arguments