反射知识点、易错点总结及练习集合_反射易错知识点-优快云博客

本文链接：https://blog.youkuaiyun.com/sinat_34692697/article/details/107882800

本文详细探讨了Java反射机制的应用，包括如何通过反射获取构造方法、成员变量和成员方法，展示了形参的可变参数特性，并深入分析了反射中私有方法及静态变量的调用注意事项。通过具体代码示例，读者可以深入了解反射机制在实际编程中的运用。

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1. 通过反射获取构造方法、成员变量、成员方法
2. 形参的可变参数
3. 反射中私有方法调用注意事项
4. 反射中静态变量及方法调用注意事项

package com.homework.classtest;

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

/**
 * @Author jinman1012@qq.com   2020/8/8 17:00
 * @Version 1.0
 */
public class CommonTest {
    public static void main(String[] args) throws NoSuchFieldException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
        //获取Student对象的Class对象
        Class clz = Student.class;
        //获取构造方法
        Constructor dc = clz.getDeclaredConstructor(int.class, double.class, String.class);
        //实例化Student对象
        Student stu = (Student)dc.newInstance(25, 180.0, "李四");
        Method studyOne = clz.getDeclaredMethod("study", String.class,int[].class);
        Method studyTwo = clz.getDeclaredMethod("study", String[].class);
        studyOne.setAccessible(true);
        studyTwo.setAccessible(true);
        studyOne.invoke(stu,"gg",new int[]{2,12,8,9});
        studyTwo.invoke(null,new Object[]{new String[]{"夕阳红","真不错，住山里真不错","CSGO磨刀石"}});
        //获取Studeng类的成员变量
        Field age = clz.getDeclaredField("age");
        Field heigt = clz.getDeclaredField("heigt");
        Field name = clz.getDeclaredField("name");
        //绕过JVM权限检测
        name.setAccessible(true);
        int getAgeValue = (int)age.get(stu);
        //静态成员变量传入任意对象都可getValue
        double getHeighValue1 = (double)heigt.get(stu);
        double getHeighValue2 = (double)heigt.get(null);
        double getHeighValue3 = (double)heigt.get("");
        double getHeighValue4 = (double)heigt.get(new String());
        //不加setAccessible(true)会报java.lang.IllegalAccessException
        String getNameValue = (String)name.get(stu);
        System.out.println(getAgeValue);
        System.out.println(getHeighValue1);
        System.out.println(getHeighValue2);
        System.out.println(getHeighValue3);
        System.out.println(getHeighValue4);
        System.out.println(getNameValue);
    }
}

//测试类
class Student {
    int age;
    static double heigt;
    private String name;

    public Student(int age, double heigt, String name) {
        this.age = age;
        this.heigt = heigt;
        this.name = name;
    }
    private void study(String name,int... arr) {
        System.out.println(name + "I'm studying.");
        int sum = 0;
        for (int i = 0; i < arr.length; i++) {
            sum += arr[i];
        }
        System.out.println(name + "I'm calculating" + sum);
    }
    private static void study(String... habits) {
        System.out.println("爱好：");
        for (int i = 0; i < habits.length; i++) {
            System.out.print(habits[i] + " ");
        }
    }
}