回顾Java知识点，面试题汇总Day11：反射、网络编程（持续更新）

一、反射通过一个实例化对象映射到类在程序运行期间就可以获取类的信息进行相关操作。1.1 Class类Class类是反射的基础用一个对象来表示某个类的信息通过Class类来创建Class是专门用来描述其他类的类每一个Class对象都是对某个类的具体描述调用forName方法通过目标类的类字面量获取通过目标类的实例化对象获取public class Test7 { public static void main(String[] args) throws Exception{ /** * 反射的三种方法 */ //forName() Class clazz1 Class.forName(User); System.out.println(clazz1); //类字面量 Class clazz2 User.class; System.out.println(clazz2); //实例化对象 User user new User(1,dyz); Class clazz3 user.getClass(); System.out.println(clazz3); System.out.println(clazz1 clazz2); System.out.println(clazz2 clazz3); } }上述3种方式获取的Class对象都是同一个因为每个类在内存中只有一份对应的对象描述内部结构的对象也只有一份。类就只有一个1.2 反射的常见方法方法描述public boolean isInterface()判断类是否为接口public boolean isArray()判断类是否为数组public boolean isAnnotation()判断类是否为注解public String getName()获取类名public ClassLoader getClassLoader()获取类加载器public Class getSuperclass()获取类的父类pubic Package getPackage()获取类所在的包public String getPackageName()获取类所在的包名public Class[] getInterfaces()获取类的接口public int getModifiers()获取类的访问权限修饰符public Field[] getFileds()获取类的全部公有成员变量包括继承父类和自定义的public Field[] getDeclareFields()获取类的自定义成员变量public Field[] getField(String name)通过名称获取类的公有成员变量public)包括继承父类和自定义的public Field[] getDeclareField(String name)通过名称获取类的自定义成员变量(自己定义的public Method[] getMethods()获取类的全部公有方法public)包括继承父类和自定义的public Method[] getDeclaredMethods()获取类的自定义方法自己定义的方法public Method getMethod(String name,Class...pars)通过名称和参数信息获取类的公有方法包括继承父类和自定义的public Method getDeclareMethod(String name,Class.. pars)通过名称和参数信息获取类的自定义方法public Constructor[] getConstructors()获取类的全部公有构造器public Constructor[] getDeclareConstructors()获取类的全部构造器public Constructor getConstructor(Class... pars)通过参数信息获取类的公有构造器public Constructor getDeclareConstructor(Class... pars)通过参数信息获取类的构造器了解package com.xlh; import java.io.*; public class Test { public static void main(String[] args) throws Exception{ Class clazz1 Class.forName(com.xlh.User); System.out.println(clazz1); //class com.xlh.User System.out.println(clazz1.isInterface()); //判断是否为接口 false System.out.println(clazz1.isArray()); //判断是否为数组 false System.out.println(clazz1.isAnnotation()); //判断是否为注解 false System.out.println(clazz1.getName());//获取类名 com.xlh.User System.out.println(clazz1.getClassLoader());//获取类加载器 jdk.internal.loader.ClassLoaders$AppClassLoader1f89ab83 System.out.println(clazz1.getSuperclass());//获取父类 Object System.out.println(clazz1.getPackage());//获取类所在的包 package com.xlh System.out.println(clazz1.getPackageName());//获取类所在的包名 com.xlh Class[] interfaces clazz1.getInterfaces(); //获取类的接口 for (Class aclazz : interfaces){ System.out.println(aclazz); //interface java.io.Serializable } int modifiers clazz1.getModifiers(); System.out.println(modifiers); //获取类的访问权限修饰符 返回1,因为只有public } }实际开发中常用Class clazz Class.forName(com.xlh.User); Field[] fields clazz.getFields(); for (Field field: fields){ System.out.println(field); //类的所有公有成员变量包括父类和自定义的 public int com.xlh.People.id public java.lang.String com.xlh.People.name } Field[] declaredFields clazz.getDeclaredFields(); for (Field declareField : declaredFields){ System.out.println(declareField); //获取自己的所有属性 不管公有还是私有 private int com.xlh.User.id private java.lang.String com.xlh.User.name } System.out.println(clazz.getField(id));//拿到的是People中的idUser中的id和name是private 拿不到 System.out.println(clazz.getDeclaredField(id));//拿去自己的属性 不管公有还是私有 获取的是User中的id二、反射的应用package test; public class Student { private int id; private String name; public int getId() { return id; } public void setId(int id) { this.id id; } public String getName() { return name; } public void setName(String name) { this.name name; } public void show(){ System.out.println(学生信息); System.out.println(ID: this.id); System.out.println(姓名 this.name); } public int test(int num,int num1){ return numnum1; } }2.1 反射调用方法package test; import java.lang.reflect.Method; public class Test { public static void main(String[] args) throws Exception{ Student student new Student(); student.setId(1); student.setName(dyz); //常规调用 student.show(); //反射调用操作方法 Class clazz Student.class; Method show clazz.getMethod(show, null); show.invoke(student,null); Method method clazz.getMethod(test, int.class,int.class); Object invoke method.invoke(student, 1, 2); System.out.println(invoke); } }2.2 反射访问成员变量package test; import java.lang.reflect.Field; import java.lang.reflect.Method; public class Test { public static void main(String[] args) throws Exception { Class clazz Student.class; Field[] declaredFields clazz.getDeclaredFields(); for (Field declaredField : declaredFields){ int modifiers declaredField.getModifiers(); Class? type declaredField.getType(); String name declaredField.getName(); System.out.println(成员变量 name 的数据类型是: type 访问权限是: getModifiers(modifiers)); } } public static String getModifiers(int modifiers){ String result null; switch (modifiers){ case 0: result; break; case 1: result public; break; case 2: result private; break; case 3: result protected; break; } return result; } }2.3 反射调用构造器私有方法不能访问通过访问公有方法反射私有属性。package test; import java.lang.reflect.Constructor; import java.lang.reflect.Field; import java.lang.reflect.Method; public class Test { public static void main(String[] args) throws Exception { Class clazz Student.class; ConstructorStudent constructor clazz.getConstructor(); //获取无参构造器不传参数 Student student constructor.newInstance(); //创建实例 Method setId clazz.getMethod(setId, int.class); setId.invoke(student,1); Method getId clazz.getMethod(getId, null); System.out.println(getId.invoke(student)); } }三、网络编程如何使用Java开发基于web的应用3.1 IP和端口IP互联网中每台终端设备都有一个唯一标识网络中的请求可以根据这个标识找到具体的终端这个唯一标识就是IP。端口8080、33063.2 TCP协议TCP协议面向连接的运输层协议比较复杂安全但效率低使用TCP协议前必须先建立连接才能传输数据数据传输完毕后释放连接。3.2.1 ServerScoket方法解释public ServerSocket(int port)根据端口创建ServerSocket对象public ServerSocket(int port,int backlog,InetAddress address)根据端口、backlog 、IP地址创建对象public Socket accpept()等待客户端请求返回Socket对象public void close()关闭ServerSocket3.2.2 Socket方法解释public Socket(String host,int port)根据主机、端口创建要连接的Socket对象public Socket(InetAddress host,int port)根据IP、端口创建要连接的Socket对象public InputStream getInputStream()获取Socket输入流public synchronized void close()关闭Socketpackage test; import java.io.DataInputStream; import java.io.DataOutputStream; import java.io.InputStream; import java.io.OutputStream; import java.net.ServerSocket; import java.net.Socket; public class Server { public static void main(String[] args) throws Exception{ ServerSocket serverSocket null; Socket socket null; InputStream inputStream null; OutputStream outputStream null; DataInputStream dataInputStream null; DataOutputStream dataOutputStream null; serverSocket new ServerSocket(8080); System.out.println(服务器端已启动等待接收); Socket accept serverSocket.accept(); // System.out.println(accept); inputStream accept.getInputStream(); dataInputStream new DataInputStream(inputStream); String request dataInputStream.readUTF(); System.out.println(接收到了客户端请求 request); String response Hello Word; outputStream accept.getOutputStream(); dataOutputStream new DataOutputStream(outputStream); dataOutputStream.writeUTF(response); System.out.println(给客户端做出回应 response); //关闭 accept.close(); serverSocket.close(); inputStream.close();; outputStream.close(); dataOutputStream.close(); dataInputStream.close(); } }package test; import java.io.DataInputStream; import java.io.DataOutputStream; import java.io.InputStream; import java.io.OutputStream; import java.net.Socket; public class Client { public static void main(String[] args) throws Exception{ Socket socket null; InputStream inputStream null; OutputStream outputStream null; DataOutputStream dataOutputStream null; DataInputStream dataInputStream null; socket new Socket(127.0.0.1,8080); System.out.println(客户端接收); System.out.println(socket); //给服务器发消息 String msg 你好呀; System.out.println(客户端说 msg); outputStream socket.getOutputStream(); dataOutputStream new DataOutputStream(outputStream); dataOutputStream.writeUTF(msg); //接收服务器发来的消息 inputStream socket.getInputStream(); dataInputStream new DataInputStream(inputStream); String s dataInputStream.readUTF(); System.out.println(服务器响应 s); //关闭 socket.close(); inputStream.close(); outputStream.close(); dataOutputStream.close(); dataInputStream.close(); } }3.3 UDP协议TCP优点是稳定安全缺点是效率低UDP恰好相反优点是效率高缺点是不安全。3.3.1 DatagramSocket方法描述public DatagramSocket(int port)根据端口创建DatagramSocket对象public void send(DatagramPacket p)发送数据包public synchronized receive(DatagramPacket p)接收数据包3.3.2 DatagramPacket方法描述public DatagramPacket(byte buf[],int length,InetAddress address,int port)根据发送的数据、数据长度、IP地址、端口创建DatagramPacket对象public synchronized byte[] getData()获取接收的数据public synchronized int getLength()获取数据长度public synchronized int getPort()获取发送数据的Socket端口package test; import java.net.DatagramPacket; import java.net.DatagramSocket; import java.net.SocketAddress; public class TerminalA { public static void main(String[] args) throws Exception{ byte[] buff new byte[1024]; DatagramPacket datagramPacket new DatagramPacket(buff, buff.length); DatagramSocket datagramSocket new DatagramSocket(8081); datagramSocket.receive(datagramPacket); String message new String(datagramPacket.getData(),0,datagramPacket.getLength()); System.out.println(我是TerminalA终端接收到了 datagramSocket 端口 传来的数据 message); //回应B String reply 我是TerminalA,已经接收到了你传来的数据; SocketAddress socketAddress datagramPacket.getSocketAddress(); DatagramPacket datagramPacket1 new DatagramPacket(reply.getBytes(),reply.getBytes().length,socketAddress); datagramSocket.send(datagramPacket1); } }package test; import java.net.DatagramPacket; import java.net.DatagramSocket; import java.net.InetAddress; import java.net.InetSocketAddress; public class TerminalB { public static void main(String[] args) throws Exception{ String message 你好我是TerminalB。; InetAddress inetAddress InetAddress.getByName(localhost); DatagramPacket datagramPacket new DatagramPacket(message.getBytes(),message.getBytes().length,inetAddress,8081); DatagramSocket datagramSocket new DatagramSocket(8080); datagramSocket.send(datagramPacket); //接受到A的回应 byte[] bytes new byte[1024]; DatagramPacket datagramPacket1 new DatagramPacket(bytes, bytes.length); datagramSocket.receive(datagramPacket1); String reply new String(datagramPacket1.getData(),0,datagramPacket1.getLength()); System.out.println(我是TerminalB接收到了 datagramPacket1.getPort() 发送来的数据 reply); } }3.4 多线程的网络编程package test; import java.net.ServerSocket; import java.net.Socket; public class ServerThread { public static void main(String[] args) throws Exception{ ServerSocket serverSocket new ServerSocket(8080); System.out.println(服务器启动..); while(true){ Socket socket serverSocket.accept(); new Thread(new ServerRunnable(socket)).start(); } } }package test; import java.io.DataInputStream; import java.io.IOException; import java.io.InputStream; import java.net.Socket; public class ServerRunnable implements Runnable{ private Socket socket; public ServerRunnable(Socket socket) { this.socket socket; } //input 读入 Override public void run() { InputStream inputStream null; DataInputStream dataInputStream null; try { inputStream this.socket.getInputStream(); dataInputStream new DataInputStream(inputStream); String message dataInputStream.readUTF(); System.out.println(message); } catch (IOException e) { e.printStackTrace(); }finally { try { inputStream.close(); } catch (IOException e) { e.printStackTrace(); } try { dataInputStream.close(); } catch (IOException e) { e.printStackTrace(); } } } }package test; import java.io.DataInputStream; import java.io.DataOutputStream; import java.io.IOException; import java.io.OutputStream; import java.net.Socket; public class ClientRunnable implements Runnable{ private int num; public ClientRunnable(int num){ this.num num; } Override public void run() { Socket socket null; OutputStream outputStream null; DataOutputStream dataOutputStream null; try { socket new Socket(localhost,8080); String message 我是客户端 this.num; outputStream socket.getOutputStream(); dataOutputStream new DataOutputStream(outputStream); dataOutputStream.writeUTF(message); } catch (IOException e) { e.printStackTrace(); } finally { try { socket.close(); } catch (IOException e) { e.printStackTrace(); } try { outputStream.close(); } catch (IOException e) { e.printStackTrace(); } try { dataOutputStream.close(); } catch (IOException e) { e.printStackTrace(); } } } }package test; public class ClientThread { public static void main(String[] args) { for (int i 0; i 10; i) { new Thread(new ClientRunnable(i)).start(); } } }