java - 使用反射来调用采用不同参数的方法

Question

我在一个类中有两个方法，一个采用 Comparable[] 作为参数并返回一个 Boolean 值。另一个方法采用 Comparable[] 和一个 int 值，返回一个 Boolean。我尝试编写一些方法来使用反射调用这些方法。

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

public class MethodCalling {
    private static Class classTocall;
    private static Method methodTocall;

    public MethodCalling(String classname){
        super();
        try {
            this.classTocall = Class.forName(classname);
        } catch (ClassNotFoundException e) {
            System.out.println("failed to get class!!");
            e.printStackTrace();
        }
    }

    public void setMethod(String method,Class...args){
        try {
            this.methodTocall = this.classTocall.getMethod(method, args);
        } catch (SecurityException e) {

            e.printStackTrace();
        } catch (NoSuchMethodException e) {

            e.printStackTrace();
        }
    }

    public Object callMethod(Object...args){
        Object result = null;

        try {
            if(this.methodTocall != null){
                result = this.methodTocall.invoke(null, new Object[]{args});

            }
        } catch (IllegalArgumentException e) {

            e.printStackTrace();
        } catch (IllegalAccessException e) {

            e.printStackTrace();
        } catch (InvocationTargetException e) {

            e.printStackTrace();
        }
        return result;
    }

    public static void main(String[] args) {
        String[] a = new String[]{"H","E","L","L","O"};
        MethodCalling mc = new MethodCalling("SizeChecker");
        mc.setMethod("isTooBig", Comparable[].class);
        Boolean result1 = (Boolean) mc.callMethod(a);
        System.out.println("too big="+result1);


        mc.setMethod("isCorrectLength",Comparable[].class,int.class);
        Boolean result2 = (Boolean) mc.callMethod(a,5);
        System.out.println("length is 5="+result2);
    }
}

class SizeChecker{  
    public static boolean isTooBig(Comparable[] a){
        return a.length > 10;
    }   
    public static boolean isCorrectLength(Comparable[] a,int x){
        return a.length == x;       
    }
}

第一个方法调用(即 isTooBig())在参数(String[])被包裹在 Object[] 中时起作用 .. 但是对于采用 String[] 和 int..

的下一个方法调用，这会失败

我该如何纠正这个问题？

Answer 1

1. 在callMethod中，args已经是一个数组。你不需要包装它:

   result = this.methodTocall.invoke(null, args);
   

2. 在 main 中，警告(在 Eclipse 中)非常清楚:

   The argument of type String[] should explicitly be cast to Object[] for the invocation of the varargs method callMethod(Object...) from type MethodCalling. It could alternatively be cast to Object for a varargs invocation

   或者javac给出的警告

   warning: non-varargs call of varargs method with inexact argument type for last parameter;

   Boolean result1 = (Boolean) mc.callMethod(a);
                                            ^
   

   cast to Object for a varargs call

   cast to Object[] for a non-varargs call and to suppress this warning

   解决方法:

   Boolean result1 = (Boolean) mc.callMethod((Object) a);