getDeclaredMethod 和 getMethod 的区别

getDeclaredMethod()获取的是类自身声明的所有方法，包含public、protected和private方法。getMethod()获取的是类的所有共有方法，这就包括自身的所有public方法，和从基类继承的、从接口实现的所有public方法。

实例一

getDeclaredMethod 和 getMethod 的区别

package com.system.net.reflect;

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

public class Say {

    public void say(String methodStr, String name, int age) throws SecurityException, IllegalArgumentException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InvocationTargetException {
        //  Method method = this.getClass().getMethod("say" + methodStr, new Class[]{String.class,int.class});              //1
        Method method = this.getClass().getDeclaredMethod("say" + methodStr, new Class[]{String.class, int.class});      //2
        method.invoke(this, new Object[]{name, age});
    }

    public void sayHello(String name, int age) {
        System.out.println("hello " + name + ",I know you are " + age);
    }

    protected void sayHi(String name, int age) {
        System.out.println("hi " + name + ",I know you are " + age);
    }

    private void sayBye(String name, int age) {
        System.out.println("bye " + name + ",I know you are " + age);
    }

    public static void main(String[] args) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException {
        new Say().say("Hello", "name1", 22);
        new Say().say("Hi", "name2", 22);
    }
}

当使用say方法里的 //1 注解语句时，main函数抛出异常，可见使用getMethod时，因为sayHi是保护方法，获取方法sayHi失败

hello jianjianjiao,I know you are 22
Exception in thread "main" java.lang.NoSuchMethodException: pkg.reflection.Say.sayHi(java.lang.String, int)
    at java.lang.Class.getMethod(Unknown Source)
    at pkg.reflection.Say.say(Say.java:9)
    at pkg.reflection.SayTest.main(SayTest.java:27)

当使用say方法里的//2语句时，可以正常调用

hello jianjianjiao,I know you are 22
hi jianjianjiao,I know you are 22

可见，不能用java.lang.Class.getMethod方法获取自身的非public方法，用java.lang.Class.getDeclaredMethod方法可以。

实例二

getDeclaredMethods 和 getMethods的区别

package com.system.net.reflect;

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

public class ReflectionUtils {

    public static void getMethodDeclaration(Class<?> clazz) {
        Method[] methods = clazz.getDeclaredMethods();
        System.out.println("MethodDeclaration in " + clazz.getName());
        for (Method method : methods) {
            method.setAccessible(true);
            System.out.println(method.getName());
        }
    }

    public static void getMethod(Class<?> clazz) {
        Method[] methods = clazz.getMethods();
        System.out.println("Method in " + clazz.getName());
        for (Method method : methods) {
            System.out.println(method.getName());
        }
    }

    public static void main(String[] args) throws SecurityException, IllegalArgumentException, NoSuchMethodException, IllegalAccessException, InvocationTargetException {
        ReflectionUtils.getMethod(Say.class);
        ReflectionUtils.getMethodDeclaration(Say.class);
    }
}

输出：

Method in pkg.reflection.Say
say
sayHello
wait
wait
wait
equals
toString
hashCode
getClass
notify
notifyAll
MethodDeclaration in pkg.reflection.Say
say
sayHello
sayHi
sayBye

可见

• getMethods 方法输出的是自身的public方法和父类Object的public方法。
• getDeclaredMethods方法输出的是自身的public、protected、private方法。

项目已分享到git上: https://github.com/orchome/net