java>反射初体验

    public static void main(String args[])
    {
        Class c = null;
        Package p = null;
        Constructor constructors[];
        Field fields[];
        Method methods[];
        
        int i,j;
        
        try{
            c = Class.forName("java.net.URLDecoder");
            
            //输出的package的名称
            System.out.println("package:");
            p = c.getPackage();
            if(p != null)
            {
                System.out.println(p.getName());
            }
            
            // 输出class或interface的名称，及其修饰符(modifiers)
            System.out.println();
            System.out.println("class:");
            int mod = c.getModifiers();
            System.out.print(Modifier.toString(mod)); //整个modifier
            if(Modifier.isInterface(mod))
            {
                System.out.print(" ");       //modifier内已经包含关键词 "interface"
            }
            else
            {
                System.out.print(" class "); //关键词 "class"
            }
            System.out.println(c.getName());
            
            
            //输出构造函数
            System.out.println();
            System.out.println("constructors:");
            constructors = c.getConstructors();
            for(i=0; i<constructors.length; i++)
            {
                
                //System.out.print(constructors[i].toGenericString());
                //上述语句输出：public java.util.LinkedList(java.util.Collection<? extends E>)
                
                //下面的语句合作输出：public java.util.LinkedList(java.util.Collection arg0)
                //这两种方法的输出结果大同小异
                System.out.print(Modifier.toString(constructors[i].getModifiers()));
                System.out.print(" " + constructors[i].getName());
                System.out.print("(");
                Class cx[] = constructors[i].getParameterTypes();
                if(cx.length >= 1)
                {
                    System.out.print(cx[0].getName());
                    System.out.print(" arg0");
                }
                for(j=1; j<cx.length; j++)
                {
                    System.out.print(", " + cx[j].getName());
                    System.out.print(" arg" + j);
                }
                System.out.println(")");
                
            }
            
            //输出变量
            System.out.println();
            System.out.println("variables:");
            fields = c.getDeclaredFields();
            for(i=0; i<fields.length; i++)
            {
                System.out.print(Modifier.toString(fields[i].getModifiers()));
                System.out.print(" " + fields[i].getType().getName());
                System.out.println(" " + fields[i].getName());
            }
            

            //输出方法
            System.out.println();
            System.out.println("methods:");
            methods = c.getDeclaredMethods();
            for(i=0; i<methods.length; i++)
            {
                System.out.print(Modifier.toString(methods[i].getModifiers()));
                Class returnClass = methods[i].getReturnType();
                System.out.print(" " + returnClass.getName() + " " + methods[i].getName() + "(");
                
                Class cx[] = methods[i].getParameterTypes();
                if(cx.length >= 1)
                {
                    System.out.print(cx[0].getName());
                    System.out.print(" arg0");
                }
                for(j=1; j<cx.length; j++)
                {
                    System.out.print(", " + cx[j].getName());
                    System.out.print(" arg" + j);
                }
                
                System.out.println(")");            
            }
            
            
            //输出父类
            System.out.println();
            System.out.println("super class:");
            Class superClass = c.getSuperclass();
            if(superClass != null)
            {
                System.out.println(superClass.getName());    
            }
            
            //输出实现的接口
            System.out.println();
            System.out.println("implemented interfaces:");
            Class interfaces[] = c.getInterfaces();
            for(i=0; i<interfaces.length; i++)
            {
                System.out.print(interfaces[i].getName() + ", ");
            }
            System.out.println();
            
            //输出inner classes
            System.out.println();
            System.out.println("inner classes:");
            Class innerClasses[] = c.getDeclaredClasses();
            for(Class innerClass : innerClasses)
            {
                System.out.print(innerClass.getName() + ", ");
            }
            System.out.println();
            
            //输出outer classes
            System.out.println();
            System.out.println("outer classes:");
            Class outerClass = c.getDeclaringClass();
            if(outerClass != null)
                System.out.println(outerClass.getName());
            else
                System.out.println("null");

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

运行结果如下图：