利用反射机制：分析类能力

package reflection;

import java.util.Scanner;
import java.lang.reflect.Constructor;
import java.lang.reflect.Modifier;
import java.util.Date;
import java.lang.reflect.Method;
import java.lang.reflect.Field;

public class ReflectionTest {
    public static void main(String[] args) {
        String name;
        if (args.length > 0) {
            name = args[0];
        } else {
            Scanner in = new Scanner(System.in);
            System.out.println("Enter class name(e.g java.util.Date)");
            //输入一个类名
            name = in.next();
        }
        try {
            Class cl = Class.forName(name); //类类型对象
            Class supercl = cl.getSuperclass(); //取得父类
            System.out.print("class " + name);
            if (supercl != null && supercl != Object.class) { //如果有父类的话
                System.out.print("extends" + supercl.getName());
            }
            System.out.print("\n{\n"); //回车：\n
            printConstructors(cl);
            printMethods(cl);
            
            System.out.println();
            printFields(cl);
            System.out.print("}");

        } catch (java.lang.ClassNotFoundException e) {
            e.printStackTrace();
        }

        System.exit(0);

    }

    public static void printConstructors(Class cl) { //打印构造器
        Constructor[] constructor = cl.getDeclaredConstructors(); //取得全部本类构造
        //for(Constructor c:constructor)
        for (int i = 0; i < constructor.length; i++) { //遍历
            String name = constructor[i].getName();
            System.out.print(" " +
                             Modifier.toString(constructor[i].getModifiers())); //取得修饰符
            System.out.print(" " + name + "("); //构造器名

            Class[] paramTypes = constructor[i].getParameterTypes(); //参数

            for (int j = 0; j < paramTypes.length; j++) {
                if (j > 0) {
                    System.out.print(","); //如果参数大于1
                }
                System.out.print(paramTypes[j].getName());
            }
            System.out.println(");");
        }
    }

    public static void printMethods(Class cl) { //打印其类所有方法
        Method[] methods = cl.getDeclaredMethods();

        for (Method m : methods) {
            Class retType = m.getReturnType();
            String name = m.getName();

            System.out.print(" " + Modifier.toString(m.getModifiers())); //修饰符
            System.out.print(" " + retType.getName() + " " + name + "("); //方法名

            Class[] paramTypes = m.getParameterTypes(); //参数
            for (int j = 0; j < paramTypes.length; j++) {
                if (j > 0) {
                    System.out.print(", ");
                }
                System.out.print(paramTypes[j].getName());
            }
            System.out.println(");");
        }
    }

    public static void printFields(Class cl) { //  方法属性/域
        Field[] field = cl.getDeclaredFields();

        for (Field f : field) {
            Class type = f.getType();
            String name = f.getName();
            System.out.print(" " + Modifier.toString(f.getModifiers())); //修饰符
            System.out.println(" " + type.getName() + " " + name + ";"); //属性名
        }
    }
}