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Java~反射的API文档使用(利用反射创建对象、反射私有构造方法、反射私有属性、反射私有方法)

程序员文章站 2024-01-21 14:33:04
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关于反射的基本介绍在我之前博客讲到过所以在这里不再多讲

点击这里跳转:反射的基本介绍

class Stuent {
    private String name = "Listen";
    public int age = 10;

    private Stuent(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public Stuent() {

    }

    public Stuent(String name) {
        this.name = name;
    }

    private void play(String game) {
        System.out.println(this.name + " 在玩" + game);
    }

    public void eat(String food, String food2) {
        System.out.println(this.name + " 在吃" + food + food2);
    }

    @Override
    public String toString() {
        return "Stuent{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

接下来我们开始使用反射,我们依旧反射上面的Student类,把反射的逻辑写到另外的类当中进行理解
注意:所有和反射相关的包都在 import java.lang.reflect包下面。

利用反射调用公有构造方法创建对象

public static void reflectNewInstance() throws ClassNotFoundException, IllegalAccessException, InstantiationException, NoSuchMethodException, InvocationTargetException {
        Class<?> classStudent = Class.forName("Stuent");
        //注意newInstance里传入的参数
        Object sudentInstance = classStudent.newInstance();
        Stuent stuent = (Stuent) sudentInstance;
        System.out.println(stuent);
        //第二种
        Stuent stuent1 = (Stuent) classStudent.newInstance();
        System.out.println(stuent1);
        //第三种
        Constructor<?> constructor = classStudent.getDeclaredConstructor(String.class);
        Stuent stuent2 = (Stuent) constructor.newInstance("Bike");
        System.out.println(stuent2);
    }

通过反射调动私有构造方法创建对象

public static void reflectPrivateConstructor() throws ClassNotFoundException, IllegalAccessException, InstantiationException, NoSuchMethodException, InvocationTargetException {
        Class<?> sutndetClass = Class.forName("Stuent");
        Constructor<?> studentConstructor= sutndetClass.getDeclaredConstructor(String.class, int.class);
        //获得权限,破坏private封装
        studentConstructor.setAccessible(true);
        Stuent stuent = (Stuent) studentConstructor.newInstance("Bike", 20);
        System.out.println(stuent);
    }

反射私有属性

public static void  reflectPrivateField() throws ClassNotFoundException, NoSuchFieldException, IllegalAccessException {
        Class<?> studentCalss = Class.forName("Stuent");
        Field field = studentCalss.getDeclaredField("name");
        //获得破坏private封装的权限
        field.setAccessible(true);
        Stuent stuent = new Stuent();
        //可以通过set来修改,也可以通过get来获取
        System.out.println(stuent);
        field.set(stuent,"Frake");
        String name = (String) field.get(stuent);
        System.out.println(name);
    }

反射私有方法

public static void reflectPrivateMethod() throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {
        Class<?> studentClass = Class.forName("Stuent");
        Method method = studentClass.getDeclaredMethod("play", String.class);
        //破坏private权限
        method.setAccessible(true);
        Stuent stuent = new Stuent();
        method.invoke(stuent, " Baketball");
        //如果不是私有方法
        Method method1 = studentClass.getDeclaredMethod("eat", String.class, String.class);
        method1.invoke(stuent, " Apple", " Banana");
    }

反射优点和缺点

优点

  1. 对于任意一个类,都能够知道这个类的所有属性和方法;对于任意一个对象,都能够调用它的任意一个方法
  2. 增加程序的灵活性和扩展性,降低耦合性,提高自适应能力
  3. 反射已经运用在了很多流行框架如:Struts、Hibernate、Spring 等等。

缺点

  1. 使用反射会有效率问题。会导致程序效率降低。
  2. 反射技术绕过了源代码的技术,因而会带来维护问题。反射代码比相应的直接代码更复杂 。

测试

   public static void main(String[] args) throws IllegalAccessException, InstantiationException, ClassNotFoundException, NoSuchMethodException, InvocationTargetException, NoSuchFieldException {
        reflectNewInstance();
        System.out.println("=============");
        reflectPrivateConstructor();
        System.out.println("=============");
        reflectPrivateField();
        System.out.println("=============");
        reflectPrivateMethod();
    }

结果:

Stuent{name='Listen', age=10}
Stuent{name='Listen', age=10}
Stuent{name='Bike', age=10}
=============
Stuent{name='Bike', age=20}
=============
Stuent{name='Listen', age=10}
Frake
=============
Listen 在玩 Baketball
Listen 在吃 Apple Banana
相关标签: Java