public class TestDemo {
//测试
@Test
public void fun01() {
TestDemo q=new TestDemo();
A a = new A();
q.adapter(a);
}
private void adapter(Base base){
HashMap<Class<? extends Base>,String> class2methodName=new HashMap<Class<? extends Base>,String>()
{
private static final long serialVersionUID = 1L;
{
put(A.class,"printA");
put(B.class,"printB");
}
};
System.out.println(class2methodName.get(base.getClass()));
invokeMethod(this,class2methodName.get(base.getClass()),new Class<?>[]{Base.class},new Object[]{base});
}
public void printA(Base base) {
A a=(A)base;
System.out.println("is A:"+a.num);
}
public void printB(Base base) {
B b=(B)base;
System.out.println("is B:"+b.num);
}
@SuppressWarnings("unchecked")
private static <T> T invokeMethod(T obj, String methodName, Class<?>[] classes, Object[] objects) {
T val = null;
try {
Method m = null;
if(objects != null && classes != null){
m = obj.getClass().getDeclaredMethod(methodName, classes);
val = (T)m.invoke(obj, objects);
}else{
m = obj.getClass().getDeclaredMethod(methodName);
val = (T)m.invoke(obj);
}
} catch (Exception e) {
e.printStackTrace();
}
return val;
}
private class Base{
public int num = 1;
}
private class A extends Base{
public int num = 2;
}
private class B extends Base{
public int num = 3;
}
}见知乎 : https://www.zhihu.com/question/66705139 也有大佬的点评
上述代码第21行 :
invokeMethod(this,class2methodName.get(base.getClass()),new Class<?>[]{Base.class},new Object[]{base});
改成:invokeMethod(this,class2methodName.get(base.getClass()),new Class<?>[]{base.getClass},new Object[]{base});就会报错,NoSuchMethodException
原因是什么?
首先看,map中有两个值,一个是{key:运行时类A,value:"printA"}{key:"运行时类B",value:"printB"}
测试方法中传的是A的对象
没改的情况 : invokeMethod(testDemo对象,"printA",运行时类A,数组存放的一个A对象)
改后的情况 : invokeMethod(testDemo对象,"printA",运行时类Base,数组存放的一个A对象)
最后执行的 invokeMethod方法中的,obj.getClass().getDeclaredMethod方法时 会出问题
public void printA(Base base) {
A a=(A)base;
System.out.println("is A:"+a.num);
}
仔细看,此方法 一个参数Base base,反射的invoke方法要求我们必须是Base对象..