【‘newInstance()‘ 已经过时了】

左手的ㄟ右手 2023-09-26 16:22 135阅读 0赞

问题：‘newInstance()’ 已经过时了

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

![在这里插入图片描述][51379bd17451449cbd291688ce93e359.png]

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);
        }
    }

[51379bd17451449cbd291688ce93e359.png]: https://img-blog.csdnimg.cn/51379bd17451449cbd291688ce93e359.png