【‘newInstance()‘ 已经过时了】-蒲公英云

【‘newInstance()‘ 已经过时了】

问题：‘newInstance()’ 已经过时了

User user = (User) class1.newInstance();

在这里插入图片描述

原因：jdk9 之后，对newInstance()做了些改变（截取了参数说明）

* @param initargs array of objects to be passed as arguments to
     * the constructor call; values of primitive types are wrapped in
     * a wrapper object of the appropriate type (e.g. a {
    @code float}
     * in a {
    @link java.lang.Float Float})
     *
     * @return a new object created by calling the constructor
     * this object represents
     * 
    @CallerSensitive
    @ForceInline // to ensure Reflection.getCallerClass optimization
    public T newInstance(Object ... initargs)
        throws InstantiationException, IllegalAccessException,
               IllegalArgumentException, InvocationTargetException
    {

解决：当前版本jdk11

package com.example.demomain.reflectstudy;
import org.junit.jupiter.api.Test;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
public class GetInstance {
    /*
     * 调用运行时类的构造器:
     * */
    @Test
    public void testConstructor() throws NoSuchMethodException, IllegalAccessException, InstantiationException, InvocationTargetException {
        //获取指定参数为String的构造器
        Constructor constructor1 = User.class.getDeclaredConstructor(String.class);
        //2.保证此构造器是可访问的
        constructor1.setAccessible(true);
        //3.调用此构造器创建运行时类的对象
        //方法一：jdk9之前
        //User user = (User)clazz.newInstance();
        //方法二：jdk9之后： 参数为 Constructor 指定的构造参数
        User user = (User) constructor1.newInstance("lfsun");
        user.print();
        //获取指定无参构造器
        Constructor constructor2 = User.class.getDeclaredConstructor();
        constructor2.setAccessible(true);
        User user1 = (User) constructor2.newInstance();
        // 引用类型默认为 null
        user1.print();
    }
}

涉及到的实体类：

package com.example.demomain.reflectstudy;
/**
 * @author lfsun
 */
public class User {
    private String userName;
    User(String userName) {
        this.userName = userName;
    }
    User() {
    }
    public void print() {
        System.out.println("Hello World " + userName);
    }
}