JDK7主要特性介绍
jdk7&8 的架构图
JDK7新增特性
1、Java 编程语言特性
- 1.1二进制数字表达方式
the integral types (byte, short, int, and long) can also be expressed using the binary number system。例如：
byte aByte = (byte)0b00100001; // An 8-bit 'byte' value short aShort = (short)0b1010000101000101; // A 16-bit 'short' value: int anInt1 = 0b10100001010001011010000101000101; // Some 32-bit 'int' values int anInt2 = 0b101; int anInt3 = 0B101; // The B can be upper or lower case.1.2 使用下划线对数字进行分隔表达，例如1322222可表示： 1_322_222
- 1.3 switch 语句支持字符串变量，例如：switch (String str) {...}
- 1.4 泛型实例创建的类型推断,例如：
Map使用可变参数时，提升编译器的警告和错误信息
- 1.5 try-with-resources 语句
说明：The try-with-resources statement is a try statement that declares one or more resources. A resource is as an object that must be closed after the program is finished with it. The try-with-resources statement ensures that each resource is closed at the end of the statement. Any object that implements java.lang.AutoCloseable, which includes all objects which implement java.io.Closeable, can be used as a resource
格式：
try(// open resources here){ // use resources } catch (FileNotFoundException e) { // exception handling } // resources are closed as soon as try-catch block is executed.优点：
- 代码的可读性更好，更易于编写代码
- 自动化的资源管理
- 代码的行数被减少
- 不需要使用finally块来关闭资源
我们可以通过在try-with-resources中使用分号来间隔多个资源，例子:
try (
BufferedReader br = new BufferedReader(new FileReader("C:\\python.txt"));
java.io.BufferedWriter writer=java.nio.file.Files.
newBufferedWriter(FileSystems.getDefault().getPath("C:\\journaldev.txt"),
Charset.defaultCharset())) {
System.out.println(br.readLine());
} catch (IOException e){
e.printStackTrace();
}
1.6 同时捕获多个异常处理 1）Handling More Than One Type of Exception：a single catch block can handle more than one type of exception，例如：catch (IOException|SQLException ex) {} 2）Rethrowing Exceptions with More Inclusive Type Checking：rethrow exception allows you to specify more specific exception types in the throws clause of a method declaration。例如：
package com.journaldev.util;
public class Java7MultipleExceptions {
public static void main(String[] args) {
try{
rethrow("abc");
}catch(FirstException | SecondException | ThirdException e){
//below assignment will throw compile time exception since e is final
//e = new Exception();
System.out.println(e.getMessage());
}
}
static void rethrow(String s) throws FirstException, SecondException,ThirdException {
try {
if (s.equals("First")) throw new FirstException("First");
else if (s.equals("Second")) throw new SecondException("Second");
else throw new ThirdException("Third");
} catch (Exception e) {
//below assignment disables the improved rethrow exception type checking feature of Java 7
// e=new ThirdException();
throw e;
}
}
static class FirstException extends Exception {
public FirstException(String msg) {
super(msg);
}
}
.......
static class ThirdException extends Exception {
public ThirdException(String msg) {
super(msg);
}
}
}2、并发
2.1 fork/join 框架（分而治之框架）
Fork 原始含义叉子、分叉的意思。在Linux 平台中，函数 fork()用来创建子进程，使得系统进程可以多一个执行分支; Join表示等待。fork()后系统多一个执行分支-线程，需要等待此执行分支执行完毕，才有可能得到结果，因此 join 就是表示等待。
实际使用中，如果大量使用 fork 开启线程进行处理，那么可能导致系统由过多线程而严重影响性能。故JDK给出ForkJoinPool 线程池，将fork开启线程交给ForkJoiinPool 线程池进行处理，节省系统资源。ForkJoinPool来支持将一个任务拆分成多个“小任务”并行计算，再把多个“小任务”的结果合并成总的计算结果。
ForkJoinPool是ExecutorService的实现类，因此是一种特殊的线程池。
使用方法：1)初始化 ForkJoinPool commonPool = ForkJoinPool.commonPool(); 2）执行指定任务commonPool.submit(ForkJoinTask
RecusiveAction(返回值任务)和RecusiveTask(无返回值任务） Demo见：https://www.cnblogs.com/lixuwu/p/7979480.html
2.4 IO
2.4.1 递归查找文件树
Files.walkFileTree(Path filepath,class T extends SimpleFileVisitor) DEMO：
import java.io.IOException;
import java.nio.file.FileVisitResult;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.SimpleFileVisitor;
import java.nio.file.attribute.BasicFileAttributes;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
/**
* @Description : 遍历目录树中的.java .class程序文件
*/
public class Test {
public static void main(String[] args) throws IOException {
Path path = Paths.get("");
System.out.println(path.toAbsolutePath());
String regex = "^.+?\\.(?:(?:java)||(?:class))$";
final Pattern pattern = Pattern.compile(regex);
Files.walkFileTree(path, new SimpleFileVisitor() {
public FileVisitResult visitFile(Path file,
BasicFileAttributes attrs) throws IOException {
String f = file.toString();
Matcher m = pattern.matcher(f);
if (m.matches()) {
System.out.println(f);
}
return FileVisitResult.CONTINUE;
}
});
}
} 2.4.2 文件系统修改通知
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
import static java.nio.file.StandardWatchEventKind.*;
/**
*JDK7 文件系统修改通知机制
*/
public class TestWatcherService {
private WatchService watcher;
public TestWatcherService(Path path)throws IOException{
watcher = FileSystems.getDefault().newWatchService();
//1 newWatchService方法实例化WatchService监听服务
path.register(watcher, ENTRY_CREATE,ENTRY_DELETE,ENTRY_MODIFY);
//2 目录注册，watcher监听目录操作事件创建、删除、修改
}
public void handleEvents() throws InterruptedException{
while(true){
WatchKey key = watcher.take();
for(WatchEvent event : key.pollEvents()){
WatchEvent.Kind kind = event.kind();
//3 获取事件Event，Event :ENTRY_CREATE,ENTRY_DELETE,ENTRY_MODIFY
if(kind == OVERFLOW){//事件可能lost or discarded
continue;
}
WatchEvent e = (WatchEvent)event;
Path fileName = e.context();
System.out.printf("Event %s has happened,
which fileName is %s%n" ,kind.name(),fileName);
}
if(!key.reset()){
break;
}
}
}
}
PS:https://www.journaldev.com/588/java-switch-case-string