Java反射之调用内部类

Posted 2020-11-02 blue星空

java反射、内部类

1. 反射调用默认访问权限的内部类

package com.blueStarWei.invoke;

import java.lang.reflect.Method;

import com.blueStarWei.invoke.OuterClass.InnerClass;

class OuterClass {
    public void func(){
        System.out.println("Outer Class.");
    }
    
    class InnerClass {
        private String mName;
        public InnerClass(String mName) {
            this.mName = mName;
        }
        void getName(){
            System.out.println("Name is : "+mName);
        }
        
    }
}


public class OuterInnerClass {

    public static void main(String[] args) {
        try {
            /*通过反射实例化内部类
             * 强大之处在于：当内部类私有化（private class InnerClass）时，也可以调用
             * */
            Class outerClass = Class.forName("com.blueStarWei.invoke.OuterClass");
            Class innerClass = Class.forName("com.blueStarWei.invoke.OuterClass$InnerClass");
            Method method = innerClass.getDeclaredMethod("getName");
            //TODO study it
            //内部类newInstance的第一个参数必须是外部类实例的引用
            method.invoke(innerClass.getDeclaredConstructors()[0].newInstance(outerClass.newInstance(),"Wei"));//Name is : Wei
            
            /*常规方法实例化内部类
             * 当内部类私有化时，无法通过该方式实例化内部类
             * */
            OuterClass outerClass1 = new OuterClass();
            InnerClass innerClass1 = outerClass1.new InnerClass("David");
            innerClass1.getName();//Name is : David
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

 

2. 反射调用静态内部类

package com.blueStarWei.invoke;

import java.lang.reflect.Method;

class OuterClass {
    public void func(){
        System.out.println("Outer Class.");
    }
    
    static class InnerClass {
        private String mName;
        public InnerClass(String mName) {
            this.mName = mName;
        }
        void getName(){
            System.out.println("Name is : "+mName);
        }
    }
}


public class StaticInnerClass {

    public static void main(String[] args) {
        try {
            /*通过反射实例化内部类 */
            Class outerClass = Class.forName("com.blueStarWei.invoke.OuterClass");
            Class innerClass = Class.forName("com.blueStarWei.invoke.OuterClass$InnerClass");
            Method method = innerClass.getDeclaredMethod("getName");
            //静态内部类没有持有外部类的引用，不需要传递外部类实例对象的引用
            method.invoke(innerClass.getDeclaredConstructors()[0].newInstance("Wei"));//Name is : Wei
            
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

 

3. 反射调用匿名内部类

package com.blueStarWei.invoke;

class OuterClass {
    public Runnable runnable = new Runnable() {
        @Override
        public void run() {
            System.out.println("This is InnerClass.");
        }
    };
}

public class AnonymousInnerClass {
    public static void main(String[] args) {
        try {
            Class outerClass = Class.forName("com.blueStarWei.invoke.OuterClass");
            //将匿名内部类当作外部类的成员变量
            Runnable runnable = (Runnable) outerClass.getDeclaredField("runnable").get(outerClass.newInstance());
            runnable.run();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

 

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