java反射调用方法
1、Talk is cheap.Show me the code.
code:
package chapter3;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
/**
* Created by MyWorld on 2016/3/16.
*/
public class RefactorInvokeMethodDemo {
public static void main(String[] args) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException, InstantiationException {
Class<Business> businessClass = Business.class;
Business business = businessClass.newInstance();
Method sayHelloMethod = businessClass.getDeclaredMethod("sayHello", String.class);
Object result = sayHelloMethod.invoke(business, "Baidu文库");
System.out.println(result);
}
}
class Business {
public String sayHello(String guestName) {
return "Hello ," + guestName;
}
}
2、执行上面的代码，看看会输出的结果是什么？
是不是期待的“Hello ,Baidu文库”
还是真是！！！
应该是嘛，完全是按api来的喽
3、知其然，知其所以然后。
来分析下代码：
（1）获取一个类定义：Business.class
（2）根据类定义，实例化一个实例business：businessClass.newInstance();
（3）根据类定义，使用api getDeclaredMethod获取指定的Method
（4）调用获取的Method:sayHelloMethod.invoke(business, "Baidu文库");
4、能不调用private的方法呢？
是可以的。
Show the code.
Code:
private String sayHello(String guestName) {
return "Hello ," + guestName;
}
5、执行上面的代码，看看是否能调用成功
报错了。。。
错误信息：
Exception in thread "main" java.lang.IllegalAccessException: Class chapter3.RefactorInvokeMethodDemo can not access a member of class chapter3.Business with modifiers "private"
at sun.reflect.Reflection.ensureMemberAccess(Reflection.java:65)
at java.lang.reflect.Method.invoke(Method.java:588)
at chapter3.RefactorInvokeMethodDemo.main(RefactorInvokeMethodDemo.java:15)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134)
6、哦。还需要设置一个地方,更改方法的private属性
Code:
Method sayHelloMethod = businessClass.getDeclaredMethod("sayHello", String.class);
sayHelloMethod.setAccessible(true);
7、执行最新的代码，看看是否正常了。
ok，看到熟悉的输出结果了！
O了！
