杰普Core Java课程笔记3
——年金波老师上课笔记
输入输出实例(利用PrintWriter与Scanner) 2
输入/输出(IO)
IO编程步骤
三步骤：
1.制定input & output
2.对input & output 进行读写
3.回收input & output 的资源（os级别开辟的资源）
source & idestination:文件 网络
流：将input output进行连接
input&output相对程序来说
字符流：文本文件（人类可识别）(Writer、Reader)
字节流：二进制文件（视频 音频 图片）(InputStream、OutputStream)
本质上的都是二进制，java默认使用utf-8作为字符的默认编码，一个utf-8字符占用两个字节
DateInputStream DateOnputStream :专门处理原始类型 readInt() readLong() writeInt() writeLong()
抽象类：InputStream OutputStream
对原始数据的读写，采用流InputStream和OutputStream,对各种基本数据类型和String类型的读写，采用流DataOutputStream和DataInputStream;对象读写采用流ObjectInputStream和ObjectOutputStream。
序列化，将内存中的对象转换为二进制的形式进行存储（java独有） ObjectOutputStream.write
PipedInputStream：线程间的通信
FileInputStream ifs=new FileInputStream("E：\\a.txt");
InputStreamReader isr=new InputStreamReader(fis);
BufferedReader br= new BufferedReader(isr);
Scanner: 字符输入
PrintWriter：字符输出 java.util.
输入输出实例(利用PrintWriter与Scanner)
package ch08;
import java.io.PrintWriter;
import java.util.Scanner;
public class ScannerTest
{
public static void main(String []args)
{
Scanner scanner=new Scanner(System.in);
PrintWriter pw=new PrintWriter(System.out);
System.out.println("plz input something:");
while(scanner.hasNextLine())
{
String input=scanner.nextLine();
if(input.equals("exit"))
{
System.exit(0);
}
pw.println("You just input:"+input);
pw.flush(); //刷新，对于支持缓存的流来说，要及时的进行刷新，
}
pw. close(); //关闭输出流
scanner.close(); //关闭输入流
}
}
对标准输入输出重定向：
输出：默认情况是终端。
重定向：System.setIN(InputStream in);
System.setOut(PrintStream out);
PrintStream ps=new PrintStream(new File("a.txt"));
System.setOut(ps);
System.out.println("HW");HW显示在a.txt中。不显示在终端。
字符编码：在linux平台下。系统默认的编码是utf-8（国际编码 二个字节表示）
在win平台下，系统默认的编码是GB2312（同GBK）国标码
iso-8859-1 latin-1 （表示西欧字符集）
字节流
ch11/ArrayCopyTest.java
阀值：
对于字节流的操作：主要通过改变缓冲区大小来提高效率
线程通信：PipedInputStream
PipedOutputStream
ch11/PipedStreamTest.java
package ch08;
import java.io.*;
public class PipedStreamTest
{
public static void main(String []args) throws Exception
{
PipedInputStream pis=new PipedInputStream();
PipedOutputStream pos=new PipedOutputStream();
pis.connect(pos);
new Sender(pos);
new Reciever(pis);
}
}
class Sender implements Runnable
{
private PipedOutputStream pos;
public Sender(PipedOutputStream pos)
{
this.pos=pos;
new Thread(this).start();
}
public void run()
{
BufferedOutputStream bos=new BufferedOutputStream(pos);
DataOutputStream dos=new DataOutputStream(bos);
for(int i=0;i<100;i++)
{
try{
dos.writeInt(i); //向Reciever线程发送
try{
Thread.currentThread().sleep(100);
}
catch(InterruptedException e)
{
e.printStackTrace();
}
System.out.println("Send:" +i);
dos.flush();
}
catch(IOException e){
e.printStackTrace();
}
}
try{
dos.close();
bos.close();
}
catch(Exception e){
e.printStackTrace();
}
}
}
class Reciever implements Runnable
{
private PipedInputStream pis;
public Reciever(PipedInputStream pis)
{
this.pis=pis;
new Thread(this).start();
}
public void run()
{
BufferedInputStream bis=new BufferedInputStream(pis);
DataInputStream dis=new DataInputStream(bis);
for(int i=0;i<100;i++)
{
try{
int result=dis.readInt(); //读取
System.out.println("Recived:" +result);
}
catch(IOException e){
e.printStackTrace();
}
}
try{
dis.close();
bis.close();
}
catch(Exception e){
e.printStackTrace();
}
}
}
序列化
序列化：ObjectOutputStream
反序列化：ObjectInputStream
对于要序列话的对象必须实现java.io.Serializebale
package ch11;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
public class SerialTest {
public static void main(String args[]) {
String fileNameString = "em.ser";
Employee emplpyee = new Employee();
emplpyee.setAge(99);
emplpyee.setName("john");
emplpyee.setGender(true);
try {
emplpyee.save(fileNameString);
outEm(fileNameString);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public static void outEm(String fileName) throws Exception {
FileInputStream fis = new FileInputStream(fileName);
ObjectInputStream ois = new ObjectInputStream(fis);
Object obj = ois.readObject();/* 反序列化 */
Employee employee = (Employee) obj;
System.out.println("From file em info:");
System.err.println("Name:" + employee.getName());
System.err.println("Age:" + employee.getAge());
System.err.println("Gender:"
+ ((employee.getGender() == true) ? "Male" : "Female"));
}
}
class Employee implements java.io.Serializable {
private String name;
private int age;
private boolean gender;
public Employee() {
super();
}
public Employee(String name, int age, boolean gender) {
super();
this.name = name;
this.age = age;
this.gender = gender;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public boolean getGender() {
return gender;
}
public void setGender(boolean gender) {
this.gender = gender;
}
public String toString() {
return this.getName() + this.getAge() + this.getGender();
}
public void save(String fileName) throws Exception {
FileOutputStream fos = new FileOutputStream(fileName);
ObjectOutputStream oos = new ObjectOutputStream(fos);
oos.writeObject(this);
oos.flush();
oos.close();
fos.close();
}
}
两个静态方法：
1.将1000个employee放入list中，然后序列化（List）
2。经list反序列化。然后打印出1000个。
transient：对于要序列化的对象，用它修饰属性的话不会被序列化。
RandomAccessFiles:随机访问文件 可以访问文件中的任意一个字节
文件指针：文件指针的位置就是下一次read的开始位置。 java。io
seek(long postition)
0:开始位置
end：文件的字节总数
seek(0);read();//读第一个字节内容
ch08/RandomAccessFileTest.java :byte的所有数字 -128～127
//byte的所有数字 -128 ~ 127 ,向文件中写入byte类型数据
package ch08;
import java.io.*;
public class RandomAccessFileTest
{
public static void main(String []args) throws Exception
{
File file=new File("ch08/raf.db");
RandomAccessFile raf=new RandomAccessFile(file,"rw");
//for(int i=-128;i<128;i++)
//for(byte i=-128;i<128;i++) //这样会死循环
for(byte i=-128;i<127;i++)
{
raf.writeByte(i);
if(i==126)
{
raf.writeByte(127);
}
System.out.println(i);
}
raf.seek(255);
int result=raf.readByte();
System.out.println(result);
System.out.println("File-Pointer Loc:"+ raf.getFilePointer());
raf.close();
}
}
Java网络编程
socket:由操作系统来分配和管理
port:telnet 23
oracle:1521
port：1～1024 系统端口
1～65535 应用端口
七层模型： osi
TCP：握手， 保证通信的有效性 稳定
UDP：不保证一定能收到消息 速度上的高效 适合做视频，实时性较高的系统 对网络要求高
java里
TCP：ServerSocket 服务器端
Socket 客户端
UDP：DategramSocket 用于通信
DategramPacket 用于数据（发送和接受网络udp包）
java.net.*
ServerSocket ss=new ServerSocket(9999);
Socket socket=ss.accept(); //socket 用来与连接到服务器端的客户端进行通信
64.135.24.33
客户端
Scoket socket=new Socket(服务器的ip，服务的端口号);
InputStream=socket.getInputStream() //获取输入流，用来读取服务器的输出
OutputStrem=socket.getOutputStream();//获取输出流，用来想服务器发送数据
Tcp实例
Ch09\ TCPserver.java
package ch09;
import java.io.*;
import java.net.*;
import java.util.Scanner;
public class TCPserver
{
public static void main(String []args)
{
Socket socket=null;
ServerSocket ss=null;
try{
ss=new ServerSocket(9999);
boolean flag=true;
while(flag)
{
Scanner scanner=new Scanner(System.in);
socket=ss.accept();
InputStream in=socket.getInputStream();
OutputStream out=socket.getOutputStream();
System.out.println(socket.getInetAddress().getHostAddress()+" connected");
PrintWriter pw=new PrintWriter(out);
pw.println(new java.util.Date().toLocaleString());
pw.flush();
pw.close();
if("shutdown".equals(scanner.nextLine()))
{
socket.close();
ss.close();
System.out.println("已关闭连接！");
flag=false;
break;
}
//socket.close();
//ss.close();
}
//socket.close();
//ss.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
//telnet 127.0.0.1 9999
Ch09\ TCPclient.java
package ch09;
import java.io.*;
import java.net.*;
import java.util.Scanner;
public class TCPclient
{
public static void main(String []args)
{
try{
Socket socket=new Socket("127.0.0.1",9999);
InputStream in= socket.getInputStream();
OutputStream out=socket.getOutputStream();
Scanner scanner=new Scanner(in);
while(scanner.hasNextLine())
{
String message=scanner.nextLine();
System.out.println("From Server:"+message);
}
in.close();
out.close();
socket.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
//telnet 127.0.0.1 9999
DatagramPacket 封装udp包
DatagramSocket 发送和接受udp包
html css js div -> html5 css3 js V8
flex:action script + mxml
云计算：hadoop 集群
amazon c3
google apps
UDP实例
Ch09\ UDPserver.java
package ch09;
import java.io.*;
import java.net.*;
import java.util.Scanner;
public class UDPServer
{
public static void main(String []args) throws Exception
{
DatagramPacket packet=null;
DatagramSocket socket=null;
socket=new DatagramSocket(10000); //使用10000号端口
byte[] buffer=new byte[1024];
packet=new DatagramPacket(buffer,buffer.length); //定义一个packet用于装将接收的数据
int pacCount=0;
while(true)
{
socket.receive(packet); //接收客户端发过来的数据包
pacCount++;
String string=new String(packet.getData(),0,packet.getLength());
System.out.println("From Client:"+string+" Count:"+pacCount);
}
}
}
//telnet 127.0.0.1 9999
Ch09\ UDPclient.java
package ch09;
import java.io.*;
import java.net.*;
import java.util.Scanner;
public class UDPClient
{
public static void main(String []args) throws Exception
{
DatagramPacket packet=null;
DatagramSocket socket=null;
socket=new DatagramSocket(10002); //使用10000号端口
SocketAddress address=new InetSocketAddress("127.0.0.1",10000); //构建要发送的包的地
for(int i=0;i<100;i++)
{
String string=""+i;
packet=new DatagramPacket(string.getBytes(),string.length(),address);
socket.send(packet);
System.out.println("Send:"+string+" NO."+i);
}
socket.close();
}
}
//telnet 127.0.0.1 9999
简易聊天室
Ch09\ ChatServer.java
package ch09;
import java.io.*;
import java.net.*;
import java.util.*;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.Scanner;
public class ChatServer
{
private ServerSocket ss;
private List list;
//private Queue list; //解决并发安全：方法一
private Socket socket;
private static final int PORT=9999;
private static final String WELCOME_MESSAGE="@Welcom to chat room !";
public ChatServer()
{
try
{
list=new LinkedList();
//list=new ConcurrentLinkedQueue(); //方法一：使用ConcurrentLinkedQueue解决并发安全
ss=new ServerSocket(PORT);
while(true)
{
socket=ss.accept();
add(socket);
new Handler(socket); //new一个用户连接句柄
}
}
catch(Exception e)
{
e.printStackTrace();
}
}
//内部类，代表着一个用户连接
class Handler implements Runnable
{
private Socket socket;
public Handler(Socket socket)
{
this.socket=socket;
new Thread(this).start(); //new一个线程，并启动
}
public void run()
{
InputStream in=null;
OutputStream out=null;
try
{
//while(true)
//{
in=socket.getInputStream();
out=socket.getOutputStream();
Scanner scanner=new Scanner(in);
PrintWriter pw=new PrintWriter(out); //初始化输出对象
pw.println(WELCOME_MESSAGE); //输出欢迎信息
pw.flush();
while(scanner.hasNextLine()) //持续等待用户输入，获得客户的发言信息
{
String message=scanner.nextLine();
broadcast(socket.getInetAddress().getHostAddress()+" says:"+message);
//方法二：解决并发安全
//broadcast_1(socket.getInetAddress().getHostAddress()+" says:"+message);
//广播客户的发言
}
//pw.close();
socket.close();
//}
//scanner.close();
//in.close();
//out.close();
//socket.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
//广播客户的发言(群发)
//解决并发安全问题，方法二
public void broadcast_1(String message) throws Exception
{
int size=list.size();
for(int i=0;i<size;i++)
{
Socket socket=(Socket)list.get(i);
if(socket.isClosed()) //判断socket是否被关闭
{
System.out.println("Socket is closed,the list size is:"+list.size());
remove(socket); //如果socket关闭了，就从list中删除
System.out.println("after remove,the list size is:"+list.size());
break;
}
else
{
//System.out.println("not close,list size is:"+list.size());
OutputStream out=socket.getOutputStream();
PrintWriter pw=new PrintWriter(out);
pw.println(message); //把消息写到输出流
pw.flush();
}
}
}
//广播客户的发言(群发)(使用迭代器遍历)
public void broadcast(String message) throws Exception
{
Iterator it=list.iterator();
while(it.hasNext())
{
Socket socket=(Socket)it.next();
if(socket.isClosed()) //监听
{
System.out.println("Socket is closed,the list size is:"+list.size());
remove(socket); //如果socket关闭了，就从list中删除
System.out.println("after remove,the list size is:"+list.size());
break; //解决并发安全，方法三
}
else
{
OutputStream out=socket.getOutputStream();
PrintWriter pw=new PrintWriter(out);
pw.println(message); //把消息写到输出流
pw.flush();
//pw.close();
//out.close();
}
}
}
//添加用户 上线
public void add(Object obj)
{
list.add(obj);
}
//删除用户 下线
public void remove(Object obj)
{
list.remove(obj);
}
public static void main(String []args) throws Exception
{
new ChatServer();
}
}
//服务端启动后，客户端只需在cmd中用telnet连接到服务端，即可发送聊天信息
//telnet 127.0.0.1 9999
Java 5.0新特性
java版本：1.0 -> 1.4 -> 1.5 (5.0) ->7.0
1.自动装箱拆箱
boxing -> 封装(wrappper)
封装基本类型:
int Integer
byte Byte
short short
long Long
float Float
double Double
boolean Boolean
------------之前的做法
char Charater (静态方法 处理字符)
List list=new ArrayList();
int i=0;
Integer iInteger=new Integer(i);
list.add(lInteger);
------------现在的做法
char Charater (静态方法 处理字符)
List list=new ArrayList();
int i=0;
list.add(i);
int -> Integer 封装 装箱 boxing
Integer -> 拆箱 unboxing
java5.BoxingTest.java
编译：
javac -source 1.4 -d . java5\Boxing.java
设置eclipse编译版本
在项目上点右键 -> Properties -> java compiler -> compile ocmpliance level: 1.4
javap -c java5.BoxingTest //查看java的汇编代码
老师观点：
不要一味的埋头干事，更重要的是要多抬头看路，快速的接受掌握新的东西。
没人会在乎你研究的多深，只有人会在乎你能做出东西来，搞应用不要专研得太深。
Java5\BoxingTest.java
package java5;
public class BoxingTest
{
public static void main(String []args)
{
int i=100;
Integer iInteger=i; //装箱
System.out.println(iInteger);
Integer iInteger1=new Integer(200);
int i1=iInteger1; //拆箱
System.out.println(i1);
Integer i3=-128;
Integer i4=-128; //判断是相等的
//-128 ~ 127 用双等号判断是相等的
if(i3==i4)
{
System.out.println("Equal!");
}
else
{
System.out.println("No Equal!");
}
}
}
2.增强的for循环
Java5\ ForTest.java
package java5;
import java.util.*;
public class ForTest
{
public static void main(String []args)
{
List list=new ArrayList();
list.add("abc");
list.add("xyz");
list.add("test");
for(Object obj:list) //遍历list
{
String string=(String)obj;
System.out.println(string);
}
String []strings=new String []{"core java","sql","xml","hibernate"};
System.out.println("-------------------------------");
for(String str:strings) //遍历数组
{
System.err.println(str);
}
System.out.println("-------------------------------");
Set set=new HashSet(); //遍历Set
set.add("set1");
set.add("set2");
set.add("set3");
for(Object obj:set)
{
String string=(String)obj;
System.out.println(string);
}
System.out.println("-------------------------------");
Map map=new HashMap(); //遍历Map
map.put(1,"map1");
map.put(2,"map2");
map.put(3,"map3");
for(Object obj:map.entrySet())
{
Map.Entry entry=(Map.Entry)obj;
System.out.println(entry.getKey()+"=>"+entry.getValue());
}
}
}
3.System.out.printf();
//标准格式化输出 类似C
printf("%d",100);
printf("%s","test");
java5/PrintfTest.java
package java5;
import java.util.*;
public class PrintfTest
{
public static void main(String []args)
{
int i=100;
String string="test";
System.out.printf("%d,%s,%S \n",i,string,string);
System.out.printf(i+","+string+","+string.toUpperCase()+"\n");
System.out.println(i+","+string+","+string.toUpperCase());
System.out.printf("%1$d,%2$s,%2$S,%1$d \n",i,string);
//1$代表第一个参数，2$代表第二个参数
//%d %s 格式符
}
}
java.util.Formatter
格式化日期
2011-12-07 11：31：34.
Java5\ FormatterTest.java
package java5;
import java.util.*;
public class FormatterTest
{
public static void main(String []args)
{
StringBuffer sb=new StringBuffer();
StringBuffer sb2=new StringBuffer();
StringBuffer sb3=new StringBuffer();
Formatter formatter=new Formatter(sb);
Formatter formatter2=new Formatter(sb2);
Formatter formatter3=new Formatter(sb3);
//formatter.format("%1$tY",new java.util.Date());
//System.out.println(sb);
formatter.format("%1$tY-%1$tm-%1$td %1$tD %1$tH:%1$tM:%1$tS "
+"\n %1$tr \n%1$tF \n %1$tH/%1$tI:%1$tM:%1$tS.%1$tL",new java.util.Date());
System.out.println(sb);
System.out.println("-------------------------------");
formatter2.format("%1$tY-%1$tm-%1$td %1$tD %1$tH:%1$tM:%1$tS "
+"\n %1$tr \n%1$tF \n %1$tH/%1$tI:%1$tM:%1$tS.%1$tL",System.currentTimeMillis());
System.out.println(sb2);
System.out.println("-------------------------------");
formatter3.format("%1$tY-%1$tm-%1$td %1$tD %1$tH:%1$tM:%1$tS "
+"\n %1$tr \n%1$tF \n %1$tH/%1$tI:%1$tM:%1$tS.%1$tL",Calendar.getInstance());
System.out.println(sb3);
}
}
4.静态导入
import static
java5/StaticImportTest.java
package java5;
import java.util.*;
import static java.lang.System.out;
import static java.lang.Math.*;
public class StaticImportTest
{
public static void main(String []args)
{
out.println("static import test");
out.println(PI);
out.println(abs(-1));
}
}
5.可变长度的参数
add(int a,int b)
add(int a,int b,int c)
......
add(int[] a) --> add(int... args)
java5/VarTest.java
package java5;
import java.util.*;
import static java.lang.System.out;
public class VarTest
{
public static int add(int... args)
{
int length=args.length;
int result=0;
for(int i=0;i<length;i++)
{
result+=args[i];
}
out.println("args.length:"+args.length);
return result;
}
public static void main(String... args)
{
out.println(add(1,2));
out.println(add());
out.println(add(100,200,300,800));
}
}
6.泛型 Generic
List list=new ArrayList();
list.add("string1");
list.add("string2");
list.add(new Employee()); //会报ClasscastException异常
for(Object obj:list)
{
String str=(String)obj;
out.println(str);
}
泛型的作用：
a.类型检查(编译期)
List<String> list=new ArrayList<String>();
java5/GenericTest.java
使用泛型约束自定义方法的参数
list.add(3.5);
list.add(9);
list.add("string");
sum(list);
public static int sum(List<Number> list)
{
double result=new Double(0.0f);
}
java5/VarTest.java
package java5;
import java.util.*;
import static java.lang.System.out;
public class GenericTest
{
public static void main(String... args)
{
List<String> list=new ArrayList<String>();
list.add("string1");
list.add("string2");
list.add((new java.util.Date()).toString());
for(Object obj:list)
{
//String string=(String)obj;
System.out.println(obj);
}
out.println("------------------------------");
Map<String,String> map=new HashMap<String,String>();
map.put("Hello","java");
map.put("World","sun");
map.put("HelloWorld","eclipse");
for(String str:map.keySet())
{
out.println("key:"+str+"\tvalue:"+(String)map.get(str));
}
out.println("------------------------------");
for(Object obj:map.entrySet())
{
Map.Entry entry=(Map.Entry)obj;
System.out.println(entry.getKey()+"=>"+entry.getValue());
}
out.println("------------------------------");
List<Number> list1=new ArrayList<Number>();
list1.add(5.5f);
list1.add(100);
sum(list1);
out.println("------------------------------");
Integer[] arrayInt=new Integer[]{1,100,999};
String[] arayString=new String[]{"str1","str2","str3"};
print(arrayInt);
print(arayString);
}
public static void sum(List<? extends Number> list)
{
Number result=new Float(0);
for(Number num:list)
{
//out.println("result.floatValue:"+result.floatValue());
//result=new Float(result.floatValue()+num.floatValue());
//给对象赋值,用new的方式，太浪费空间
result=result.floatValue()+num.floatValue(); //自动装箱
//out.println("result:"+result.floatValue());
out.println("result:"+result.floatValue()); //自动拆箱
}
}
//add(E element)
public static <E> void print(E [] array) //E代表可以传入任意类型,<E> 表示声明E为任意类型
{
for(Object obj:array)
{
out.println(obj);
}
}
}
cvs
--------------------------------
Alpha 版
Beta 版
Release Candidate 发布候选版
RC1
GA General Avaibility 正式版本
7.枚举 类
用来替换常量 效果跟常量是相同的
public enum Size
{
LARGE,MIDDLE,SAMLL
}
拿到Size的值
Size.LARGE
java5/EnumTest.java
package java5;
import java.util.*;
import static java.lang.System.out;
enum Size //枚举类
{
//LARGE,MIDDLE,SMALL //加个封号，和不加封号都没错,最好加封号
LARGE(50)
{
public String toString(){
return "size:large value:"+this.getValue();
}
},
MIDDLE(30)
{
public String toString(){
return "Size:middle value:"+this.getValue();
}
},
SMALL(20)
{
public String toString(){
return "Size:small value:"+this.getValue();
}
};
Size(){}
Size(int value)
{
this.value=value;
}
private int value;
public int getValue()
{
return this.value;
}
}
public class EnumTest
{
private Size size;
public EnumTest(Size size)
{
this.size=size;
}
public static void main(String... args)
{
EnumTest test=new EnumTest(Size.LARGE);
out.println(test);
}
public String toString()
{
out.println(size.toString());
return Arrays.deepToString(size.values());
}
}
8.annotation 注解
辅助程序运行 在注解中进行程序的配置
port:8888 ip:localhost
@Override :以@符号开头+注解类
主流框架产品都支持使用注解进行程序配置
xml文件配置(文本配置)
(xml,properties文件配置)
将程序的数据与程序本身分离
将程序的数据分离
使用注解的配置可验证(通过编译验证)
public String toString()
{
}
java5/OverrideTest.java
注解：三种
1. Marker Annotation:标记注解
@Override
2. Single value Annotation:单值注解
@Test(input="abc")
3. Muti Value Annotation 多值注解
@Test(input="abc",output="ABC")
4. 自定义注解：类似于类
Test.java
@Retention(RetentionPolicy.CLASS)
@Target(ElementType.METHOD)
public @interface Test
{
String input();
String output();
}
target:指定自定义的注解能够在什么地方使用
class A
{
private int age;
@Test //因为Target是被指定为METHOD
public void setAge()
{
}
}
Retention：表示注解的生命周期
source:只在于源代码中
class:只存在于class文件中
java5/Test.java
package java5;
import java.lang.annotation.*;
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Test {
String input();
String output();
}
import static java.lang.System.out;
import java.lang.annotation.*;
@Retention(RetentionPolicy.RUNTIME)
public @interface RententionTest
import static java.lang.System.out;
import java.lang.annotation.*;
@RententionTest(input="ABC",output="abc")
public static String toLowerCase(String str)
public static void main(String args[])
Class clz=AnnotationTest.class;
Method [] method=clz.getDeclaredMethods(); //得到类中的所有方法
for(int i=0;i<method.length;i++)
boolean hasAnnotation=method[i].isAnnotationPresent(RententionTest.class);
RententionTest test=(RententionTest)method[i].getAnnotation(RententionTest.class); //得Annotation
String input=test.input(); //拿到Annotation的值
String expectedOutput=test.output();
String realOutput=toLowerCase(input);
if(expectedOutput.equals(realOutput))
out.println("Test Successful");
