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java 高级特性

2018-06-29 10:38:50   0  举报

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java 高级，java 高级，java 高级

集合

文件流

作者其他创作

大纲/内容

1.集合框架

Map

HashTable 和HashMap区别

HashTable 线程安全 HashMap线程不安全

HashMap key 可以存null 值 HashTable 不可以存null 运行时异常编译能通过

HashMap put(key,value) remove(key) 改put(key,value) get(key)

HashMap集合的遍历通过key 去找value key 是一个Set 集合,所以key 是唯一的

增加for循环遍历 for (String key : map.keySet()) { String value = map.get(key); System.out.println(value); }

迭代器遍历map Iterator iter = map.keySet().iterator(); while(iter.hasNext()){ String key = (String)iter.next(); System.out.println(key); String value =(String)map.get(key); System.out.println(value); }

Collection

List 有序,不唯一

ArrayList 基于数组随机读取数据快 add(obj) remove(index) add(int,obj); get(index)

LindkedList 基于链表的集合,删除和插入效率比较高 addFirst()addLast() removeFirst() removeLast();

Vector 和ArrayList 区别 Vector 线程安全 synchronized ArrayList线程不安全

set 无序,唯一 equals()

HashSet 采用对象的equals()方法比较两个对象是否相等

Set set=new HashSet(); String s1=new String("java"); String s2=s1; String s3=new String ("java"); set.add(s1); set.add(s2); set.add(s3); System.out.println(set.size());

2.实用类

枚举 enum 用来存常量是一种类型

包装类 Interger Integer.parseInt("6");

String

String str="abc"; String str1 = new String("abc"); System.out.println(str==str1);//false System.out.println(str.equals(str1));//true

length();字符串长度

subString(start,end); 截取字符串包前不包后

str.indexOf("a"); //查找字符返回下标,找不到返回-1;

str.split(",");//分割返回时String[] 数组

str.trim();//去空格

str.equalsIgnoreCase("");//忽略大小写

str.toLowerCase();//小写

str.toUpperCase();//大写

str.replace("oldChar", "newChar");//替换

StringBuffer String StringBuilder String是不可变对象 final 类对字符串频繁修改（如字符串连接）时，使用StringBuffer类可以大大提高程序执行效率 StringBuffer 线程安全 StringBuilder 线程不安全

Date

// 创建日期对象 Date date = new Date(); // 定制日期格式 SimpleDateFormat formater = new SimpleDateFormat("yyyy- MM-dd HH:mm:ss"); //format把data类型转换成String类型 String now = formater.format(date); //parse把String类型转换成Date类型 date = formater.parse("2017-06-08 12:00:00");

Calendar 日历类

abstract 抽象类 Calendar calendar = Calendar.getInstance(); calendar.get(Calendar.DATE);

3.File IO

字节流和字符流相互转换可以解决乱码问题

FileInputStream file = new FileInputStream("D:\\aaa\\aaa.txt"); InputStreamReader ir = new InputStreamReader(file,"utf-8"); BufferedReader br = new BufferedReader(ir);

字符流所有的字符流都继承Reader Wirter

FileReader BufferedReader

Reader Wirter 读取文件类容是,使用FileReader fr = new FileReader("D:\\aaa\\aaa.txt"); BufferedReader br = new BufferedReader(fr); FileWriter fw = new FileWriter("D:\\aaa\\cc.txt"); BufferedWriter bw = new BufferedWriter(fw); String str = br.readLine(); StringBuffer sb = new StringBuffer(); while(str!=null){ sb.append(str); bw.write(str); str = br.readLine(); } System.out.println(sb.toString()); bw.close(); br.close();

字节流 ,所有的字节流,都继承于 InputStream outputStream

子类 FileInputStream DataInputStream

拷贝不需要读取文件内容是用字节流 FileInputStream input = new FileInputStream("D:\\aaa\\tuzideng1.jpg"); DataInputStream finput = new DataInputStream(input); FileOutputStream out = new FileOutputStream("D:\\aaa\\tuzideng2.jpg"); DataOutputStream fout = new DataOutputStream(out); //缓存 byte[] bytes = new byte[1024]; while (finput.read(bytes) != -1) { fout.write(bytes); } finput.close(); fout.close();

File类常用方法

boolean exists( ) 判断文件或目录是否存在

boolean isFile( )

boolean isDirectory( )

String getPath( )

String getAbsolutePath( )

String getName( )

boolean delete( )

boolean createNewFile( )

long length()

mkdirs()

反射机制

反射机制是指在运行状态中，动态的获取信息以及动态调用对象方法的功能

<span>Java反射机制提供如下功能：</span>

<span>在运行时判断任意一个对象所属的类</span>

<span>在运行时构造任意一个类的对象</span>

<span>在运行时判段任意一个类所具有的成员变量和方法</span>

<span>在运行时调用任一个对象的方法</span>

反射的基本应用

1.获得Class对象<br>

<div><div>//第一种方式：  </div><div>Class c1 = Class.forName("demo.Student");  </div></div>

<div>//第二种方式：  </div><div>//java中每个类型都有class 属性.  </div><div>Class  c2 = Student.class;  </div>

<div>//第三种方式：  </div><div>//java语言中任何一个java对象都有getClass 方法  </div><div>Student stu = new Student();  </div><div>Class c3 = stu.getClass(); //c3是运行时类 </div>

2.判断是否为某个类的实例<br>

<div><span> </span>Student stu = new Student();</div><div><span> </span>Student.class.isInstance(stu);</div>

3.创建实例

<div><span></span><span>1使用Class对象的newInstance()方法来创建Class对象对应类的实例。</span><br>Class c1 = Student.class;</div><div><span> </span>Object obj = c1.newInstance();</div><div><span> </span>Student stu = (Student)obj;</div>

<span>2先通过Class对象获取指定的Constructor对象，来创建实例。这种方法可以用指定的构造器构造类的实例。</span>

4.获取方法

5.获取构造器信息

6.获取类的成员变量（字段）信息

7.调用方法

8.利用反射创建数组

多线程

Java中创建线程的两种方式

<div>继承java.lang.Thread类</div>

<div><span> </span>// 重写run()方法</div><div><span> </span>public void run() {</div><div><span> </span>for (int i = 1; i < 100; i++) {</div><div><span> </span>System.out.println(Thread.currentThread().getName() + ":" + i);</div><div><span> </span>}</div><div><span> </span>}</div><div><span> </span>public static void main(String[] args) {</div><div><span> </span>MyThread thread = new MyThread();</div><div><span> </span>thread.start(); // 启动线程}</div><div><span> </span>}</div>

<div>实现java.lang.Runnable接口</div>

<div>public class MyRunnable implements Runnable {</div><div><span> </span>public void run() {</div><div><span> </span>for (int i = 1; i < 100; i++) {</div><div><span> </span>System.out.println(Thread.currentThread().getName() + ":" + i);</div><div><span> </span>}</div><div><span> </span>}</div><div><br></div><div><span> </span>public static void main(String[] args) {</div><div><span> </span>MyRunnable myRunnable = new MyRunnable();</div><div><span> </span>Thread myThread = new Thread(myRunnable);</div><div><span> </span>myThread.start(); // 启动线程}</div><div><span> </span>}</div><div>}</div>

线程的状态

线程调度方法

setPriority(int  newPriority)<span> </span>更改线程的优先级

<div>线程优先级由1~10表示，1最低，默认优先级为5</div><div>优先级高的线程获得CPU资源的概率较大</div>

<div>public class MyThread extends Thread {</div><div><br></div><div><span> </span>// 重写run()方法</div><div><span> </span>public void run() {</div><div><span> </span>for (int i = 1; i < 100; i++) {</div><div><span> </span>System.out.println(Thread.currentThread().getName() + ":" + i);</div><div><span> </span>}</div><div><span> </span>}</div><div><br></div><div><span> </span>public static void main(String[] args) {</div><div><span> </span>Thread t1 = new Thread(new MyThread(), "线程A");</div><div><span> </span>Thread t2 = new Thread(new MyThread(), "线程B");</div><div><span> </span>t1.setPriority(Thread.MAX_PRIORITY);</div><div><span> </span>t2.setPriority(Thread.MIN_PRIORITY);</div><div><span> </span>// 省略代码……</div><div><span> </span>}</div><div><br></div><div>}</div>

static void sleep(long millis)<span> </span>在指定的毫秒数内让当前正在执行的线程休眠

<div>让线程暂时睡眠指定时长，线程进入阻塞状态</div><div>睡眠时间过后线程会再进入可运行状态</div>

<div>public class Wait {</div><div><span> </span>public static void bySec(long s) {</div><div><span> </span>for (int i = 0; i < s; i++) {</div><div><span> </span>System.out.println(i + 1 + "秒");</div><div><span> </span>try {</div><div><span> </span>Thread.sleep(1000);</div><div><span> </span>} catch (InterruptedException e) {</div><div><span> </span>e.printStackTrace();</div><div><span> </span>}</div><div><span> </span>}</div><div><span> </span>}</div><div>}</div><div><br></div>

void join()<span> </span>等待该线程终止

使当前线程暂停执行，等待其他线程结束后再继续执行本线程

<div>public class MyThread implements Runnable {</div><div><span> </span>public void run() {</div><div><span> </span>for (int i = 0; i < 10; i++) {</div><div><span> </span>try {</div><div><span> </span>Thread.sleep(100);</div><div><span> </span>} catch (InterruptedException e) {</div><div><span> </span>// TODO Auto-generated catch block</div><div><span> </span>e.printStackTrace();</div><div><span> </span>}</div><div><span> </span>// 输出当前线程的信息</div><div><span> </span>System.out.println(Thread.currentThread().getName() + "运行：" + i);</div><div><span> </span>}</div><div><span> </span>}</div><div><br></div><div><span> </span>public static void main(String[] args) {</div><div><span> </span>System.out.println("*****线程强制执行******");</div><div><span> </span>// 创建子线程并启动</div><div><span> </span>Thread temp = new Thread(new MyThread());</div><div><span> </span>temp.start();</div><div><span> </span>for (int i = 0; i < 20; i++) {</div><div><span> </span>if (i == 5) {</div><div><span> </span>try {</div><div><span> </span>// 阻塞主线程，子线程强制执行</div><div><span> </span>temp.join();</div><div><span> </span>} catch (InterruptedException e) {</div><div><span> </span>e.printStackTrace();</div><div><span> </span>}</div><div><span> </span>}</div><div><span> </span>try {</div><div><span> </span>Thread.sleep(100);</div><div><span> </span>} catch (InterruptedException e) {</div><div><span> </span>// TODO Auto-generated catch block</div><div><span> </span>e.printStackTrace();</div><div><span> </span>}</div><div><span> </span>System.out.println(Thread.currentThread().getName() + "运行：" + i);</div><div><span> </span>}</div><div><span> </span>}</div><div>}</div>

static void yield()<span> </span>暂停当前正在执行的线程对象，并执行其他线程

<div>暂停当前线程，允许其他具有相同优先级的线程获得运行机会</div><div>该线程处于就绪状态，不转为阻塞状态<br><div>只是提供一种可能，但是不能保证一定会实现礼让</div></div>

<div>public class MyThread implements Runnable {</div><div><span> </span>public void run() {</div><div><span> </span>for (int i = 0; i < 5; i++) {</div><div><span> </span>System.out.println(Thread.currentThread().getName() + "正在运行：" + i);</div><div><span> </span>if (i == 3) {</div><div><span> </span>System.out.print("线程礼让：");</div><div><span> </span>Thread.yield();</div><div><span> </span>}</div><div><span> </span>}</div><div><span> </span>}</div><div><br></div><div><span> </span>public static void main(String[] args) {</div><div><span> </span>MyThread my = new MyThread();</div><div><span> </span>Thread t1 = new Thread(my, "线程A");</div><div><span> </span>Thread t2 = new Thread(my, "线程B");</div><div><span> </span>t1.start();</div><div><span> </span>t2.start();</div><div><span> </span>}</div><div>}</div>

void interrupt()<span> </span>中断线程

boolean isAlive()<span> </span>测试线程是否处于活动状态

线程通信方法

wait() 调用wait()方法会挂起当前线程，并释放共享资源的锁

notify() 调用任意对象的notify()方法会在因调用该对象的wait()方法而阻塞的线程中随机选择一个线程解除阻塞，但要等到获得锁后才可真正执行

notifyAll() 调用了notifyAll()方法会将调用该对象的wait()方法而阻塞的所有线程一次性全部解除阻塞

wait(),notify(),notifyAll()这三个方法都是Object类当中的final方法，被所有类继承且不允许重写。这三个方法只能在同步方法或者同步代码块中使用，否则会抛出异常

线程同步方法synchronized

<div>就是为当前的线程声明一个锁<br>使用synchronized修饰的方法控制对类成员变量的访问<br></div>

<div>访问修饰符 synchronized 返回类型方法名（参数列表）{……}</div><div>        或者</div><div>synchronized 访问修饰符返回类型方法名（参数列表）{……}</div>

<div>使用synchronized关键字修饰的代码块</div>

<div>synchronized(syncObject){</div><div>    //需要同步的代码</div><div>}</div>

java网络编程

Socket

基于TCP协议的Socket网络通信<br><div>用来实现双向安全连接网络通信<br><div>进行网络通信时，Socket需要借助数据流来完成数据的传递工作</div></div>

客户端

<div>public class ClientLogin {</div><div><span> </span>public static void main(String[] args) {</div><div><span> </span>//1.创建一个socket对象（指定服务器IP,端口号）</div><div><span> </span>try {</div><div><span> </span>Socket socket = new Socket("localhost",8000);</div><div><span> </span>//2.打开输出流,发送请求</div><div><span> </span>OutputStream os = socket.getOutputStream();</div><div><span> </span>InputStream is = socket.getInputStream();</div><div><span> </span>String info = "用户名：TOM，密码：1234";</div><div><span> </span>os.write(info.getBytes());<span> </span></div><div><span> </span>socket.shutdownOutput();</div><div><span> </span>//服务器接收客户端反馈<span> </span></div><div><span> </span>BufferedReader br = new BufferedReader(new InputStreamReader(is));</div><div><span> </span>info = "";</div><div><span> </span>while((info=br.readLine())!=null){</div><div><span> </span>System.out.println("我是客户端，服务器的响应是："+info);</div><div><span> </span>}</div><div><span> </span>os.close();</div><div><span> </span>is.close();</div><div><span> </span>socket.close();</div><div><span> </span>} catch (UnknownHostException e) {</div><div><span> </span>// TODO Auto-generated catch block</div><div><span> </span>e.printStackTrace();</div><div><span> </span>} catch (IOException e) {</div><div><span> </span>// TODO Auto-generated catch block</div><div><span> </span>e.printStackTrace();</div><div><span> </span>}</div><div><span> </span></div><div><span> </span>//3.关闭资源</div><div><span> </span></div><div><span> </span>}</div><div>}</div>

服务端

<div>public class ServerLogin {</div><div><span> </span>public static void main(String[] args) {</div><div><span> </span>//1.创建一个ServerSocket对象指定端口号</div><div><span> </span>try {</div><div><span> </span>ServerSocket serversocket = new ServerSocket(8000);</div><div><span> </span>//2.监听客户端请求</div><div><span> </span>Socket socket = serversocket.accept();</div><div><span> </span>//3.打开输入流，处理用户请求</div><div><span> </span>InputStream is = socket.getInputStream();<span> </span></div><div><span> </span>OutputStream os = socket.getOutputStream();</div><div><span> </span>BufferedReader reader = new BufferedReader(new InputStreamReader(is));</div><div><span> </span>String info = null;</div><div><span> </span>while((info=reader.readLine())!=null){</div><div><span> </span>System.out.println("我是服务器，客户端信息为："+info);</div><div><span> </span>}</div><div><span> </span>socket.shutdownInput();</div><div><span> </span>//服务器给客户端一个响应<span> </span></div><div><span> </span>//1.打开输出流，发送数据<span> </span></div><div><span> </span>info = "欢迎您，登录成功！";</div><div><span> </span>os.write(info.getBytes());</div><div><span> </span>//4.关闭资源</div><div><span> </span>reader.close();</div><div><span> </span>is.close();</div><div><span> </span>os.close();</div><div><span> </span>socket.close();</div><div><span> </span>serversocket.close();</div><div><span> </span></div><div><span> </span>} catch (IOException e) {</div><div><span> </span>// TODO Auto-generated catch block</div><div><span> </span>e.printStackTrace();</div><div><span> </span>}</div><div><span> </span></div><div><span> </span></div><div><span> </span></div><div><span> </span>}</div><div>}</div>

超文本传输协议（HTTP，HyperText Transfer Protocol)是互联网上应用最为广泛的一种网络协议<br>

<span>HTTPS（全称：Hyper Text Transfer Protocol over Secure Socket Layer），是以安全为目标的</span><a target="_blank">HTTP</a><span>通道，简单讲是HTTP的安全版。即HTTP下加入SSL层，HTTPS的安全基础是SSL，因此加密的详细内容就需要SSL。</span>

xml

<div>基于XML文档树结构的解析</div><div>适用于多次访问的XML文档</div><div>特点：比较消耗资源</div>

读取dom

<div>DocumentBuilderFactory bf = DocumentBuilderFactory.newInstance();</div><div><span> </span>DocumentBuilder db = bf.newDocumentBuilder();</div><div><span> </span>Document doc = db.parse("src/phones.xml");</div>

读取节点的属性，和文本

<div>NodeList brandList = doc.getElementsByTagName("Brand");</div><div><br></div><div><span> </span>for (int i = 0; i < brandList.getLength(); i++) {</div><div><span> </span>Node brand = brandList.item(i);</div><div><span> </span>Element element = (Element) brand;</div><div><span> </span>String attrValue = element.getAttribute("name");</div><div><span> </span>NodeList types = element.getChildNodes();</div><div><span> </span>System.out.println(types.getLength());</div><div><span> </span>for (int j = 0; j < types.getLength(); j++) {</div><div><span> </span>if (types.item(j).getNodeType() == 1) {</div><div><span> </span>Element typeElement = (Element) types.item(j);</div><div><span> </span>String type = typeElement.getTextContent();</div><div><span> </span>System.out.println("手机:" + attrValue + type);</div><div><span> </span>}</div><div><br></div><div><span> </span>}</div><div><span> </span>}</div>

创建节点，属性，文本

<div>Element brandElement = doc.createElement("Brand");</div><div><span> </span>brandElement.setAttribute("name", "MOTO");</div><div><span> </span>Element type = doc.createElement("type");</div><div><span> </span>type.setTextContent("A1680");</div><div><span> </span>brandElement.appendChild(type);</div><div><span> </span>Element pe = (Element) doc.getElementsByTagName("PhoneInfo").item(0);</div><div><span> </span>pe.appendChild(brandElement);</div>

保存xml

<div>TransformerFactory tf = TransformerFactory.newInstance();</div><div><span> </span>Transformer transformer = tf.newTransformer();</div><div><span> </span>DOMSource domSource = new DOMSource(doc);</div><div><span> </span>transformer.setOutputProperty(OutputKeys.ENCODING, "utf-8");</div><div><span> </span>FileOutputStream fos = new FileOutputStream("src/phones1.xml");</div><div><span> </span>StreamResult result = new StreamResult(fos);</div><div><span> </span>transformer.transform(domSource, result);</div>

<div>非常优秀的Java XML API</div><div>性能优异、功能强大</div><div>开放源代码</div>

读取dom

<div>SAXReader saxReader = new SAXReader();</div><div><span> </span>Document document = saxReader.read("NewFile.xml");</div>

读取节点的属性，和文本

<div>Element root =document.getRootElement();</div><div><span> </span>List<Element> brandList = root.elements();</div><div><span> </span>for(Element brand:brandList) {</div><div><span> </span>Attribute attr=<span> </span>brand.attribute("name");</div><div><span> </span>System.out.println(attr.getValue());</div><div><span> </span>List<Element> typeList = brand.elements();</div><div><span> </span>for(Element type:typeList) {</div><div><span> </span>System.out.println(type.getText());</div><div><span> </span>}</div><div><span> </span>}</div>

创建节点，属性，文本

<div> Element newBrand = root.addElement("Brand");</div><div><span> </span> newBrand.addAttribute("name", "小米");</div><div><span> </span> Element newType =  newBrand.addElement("type");</div><div><span> </span> newType.setText("小米6");</div>

保存xml

<div>OutputFormat format =OutputFormat.createCompactFormat();</div><div><span> </span>format.setEncoding("gb2312");</div><div><span> </span>FileWriter file = new FileWriter("phones2.xml");</div><div><span> </span>XMLWriter writer = new XMLWriter(file,format);</div><div><span> </span>writer.write(document);</div><div><span> </span>writer.close();</div>