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从0开始才是王道。 0. 多线程。Java支持多线程。在C/C++之类的语言还依赖操作系统的接口的时候，Java就已经有了跨平台的语言级别的多线程支持。（C++11啊，你出生得太晚了，Java都等你16年了）。 package cn.byr.nuanyangyang.java20.thread; public class ThreadTest { public static void main(String[] args) throws Exception { Thread t1 = new Thread(() -> { for (int i = 0; i < 100; i++) { System.out.println("Hello world " + i); } } ); Thread t2 = new Thread(() -> { for (int i = 0; i < 100; i++) { System.out.println("Goodbye world " + i); } } ); t1.start(); t2.start(); t1.join(); t2.join(); } } 1. 动态装载。Java支持动态类装载。在C/C++之类的语言还依赖操作系统的接口的时候，Java已经有了跨平台的安全的好用的类装载器。在Java里，“ClassLoader + 类名”共同确定一个类，而不单单是类的名称。正因如此，程序员可以在程序运行时创建新的jar包，里面有和现有代码同名的类，然后创建不同的ClassLoader来读这个新的jar包。即使如此，也不会发生命名冲突（C程序员知道我是什么意思： http://bbs.byr.cn/#!article/Linux/147332 ）这是公共的接口 // IHelloWorld.jar package cn.byr.nuanyangyang.java20.loader; public interface IHelloWorld { void greet(String name); } 把下面这个具体的实现打到loadable-hw.jar包里去。 // LoadableHelloWorld.java package cn.byr.nuanyangyang.java20.loader; public class LoadableHelloWorld implements IHelloWorld { @Override public void greet(String name) { System.out.println("Hello, " + name); } } 下面这是主程序： package cn.byr.nuanyangyang.java20.loader; import java.io.File; import java.net.URL; import java.net.URLClassLoader; public class LoaderTest { public static void main(String[] args) throws Exception { File myJar = new File("loadable-hw.jar"); URLClassLoader cl = new URLClassLoader(new URL[] { myJar.toURI().toURL() }); Class<? extends IHelloWorld> lhwCls = cl.loadClass("cn.byr.nuanyangyang.java20.loader.LoadableHelloWorld") .asSubclass(IHelloWorld.class); IHelloWorld lhw = lhwCls.newInstance(); lhw.greet("world"); cl.close(); } } 2. Unicode支持。Java支持Unicode，这对国际化非常有帮助。 package cn.byr.nuanyangyang.java20.unicode; public class UnicodeTest { public static void main(String[] args) { System.out.println("\u4e16\u754c\u4f60\u597d"); } } 3. 网络编程。Java支持网络编程，包括socket接口。当C/C++还在依赖操作系统提供的接口的时候，Java已经有了跨平台的网络编程支持。 package cn.byr.nuanyangyang.java20.socket; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.net.ServerSocket; import java.net.Socket; class Client implements Runnable { @Override public void run() { try (Socket s = new Socket("localhost", 8000)) { System.out.println("[Client] Connected to server."); try (InputStream is = s.getInputStream()) { byte[] inBuffer = new byte[256]; int sz = 0; int actualRead; while ((actualRead = is.read(inBuffer, sz, 256 - sz)) > 0) { sz += actualRead; } String str = new String(inBuffer, 0, sz, "UTF-8"); System.out.println("[Client] Received: " + str); } } catch (Exception e) { System.out.println("An exception is thrown. There is really nothing I can do about it."); e.printStackTrace(); } } } class Server implements AutoCloseable { private ServerSocket ss; public Server() throws IOException { ss = new ServerSocket(8000, 5); } public void serveOne() throws IOException { try (Socket s = ss.accept()) { System.out.println("[Server] A client connected."); String word = "Hello world!"; byte[] wordBytes = word.getBytes("UTF-8"); try (OutputStream os = s.getOutputStream()) { os.write(wordBytes); } System.out.println("[Server] Sent message to client."); } } @Override public void close() throws Exception { if (ss != null) { ss.close(); } } } public class SocketTest { public static void main(String[] args) throws Exception { try (Server server = new Server()) { Client client = new Client(); Thread clientThread = new Thread(client); clientThread.start(); server.serveOne(); clientThread.join(); } } }

[Java20年]Quiz:下列特性是哪个Java版本引入的？(0)