1、switch中添加对String类型的支持
public String generate(String name, String gender) {
String title = "";
switch (gender) {
case "男":
title = name + " 先生";
break;
case "女":
title = name + " 女士";
break;
default:
title = name;
}
return title;
}
编译器在编译时先做处理：
①case仅仅有一种情况。直接转成if。
②假设仅仅有一个case和default，则直接转换为if…else…。
③有多个case。先将String转换为hashCode，然后相应的进行处理，JavaCode在底层兼容Java7曾经版本号。
2、数字字面量的改进
Java7前支持十进制（123）、八进制（0123）、十六进制（0X12AB）
Java7添加二进制表示（0B11110001、0b11110001）
数字中可加入分隔符
Java7中支持在数字量中间添加’_‘作为分隔符。更直观，如（12_123_456）。下划线仅仅能在数字中间。编译时编译器自己主动删除数字中的下划线。
int one_million = 1_000_000;
3、异常处理（捕获多个异常） try-with-resources
catch子句能够同一时候捕获多个异常
public void testSequence() {
try {
Integer.parseInt("Hello");
}
catch (NumberFormatException | RuntimeException e) { //使用‘|‘切割，多个类型，一个对象e
}
}
try-with-resources语句
Java7之前须要在finally中关闭socket、文件、数据库连接等资源；
Java7中在try语句中申请资源，实现资源的自己主动释放（资源类必须实现java.lang.AutoCloseable接口，一般的文件、数据库连接等均已实现该接口，close方法将被自己主动调用）。
public void read(String filename) throws IOException {
try (BufferedReader reader = new BufferedReader(new FileReader(filename))) {
StringBuilder builder = new StringBuilder();
String line = null;
while((line=reader.readLine())!=null){
builder.append(line);
builder.append(String.format("%n"));
}
return builder.toString();
}
}
4、增强泛型推断
Java7之后可以简单的这么写
Map<String, List<String>> anagrams = new HashMap<>();
5、NIO2.0（AIO）新IO的支持
- bytebuffer
public class ByteBufferUsage {
public void useByteBuffer() {
ByteBuffer buffer = ByteBuffer.allocate(32);
buffer.put((byte)1);
buffer.put(new byte[3]);
buffer.putChar(‘A‘);
buffer.putFloat(0.0f);
buffer.putLong(10, 100L);
System.out.println(buffer.getChar(4));
System.out.println(buffer.remaining());
}
public void byteOrder() {
ByteBuffer buffer = ByteBuffer.allocate(4);
buffer.putInt(1);
buffer.order(ByteOrder.LITTLE_ENDIAN);
buffer.getInt(0); //值为16777216
}
public void compact() {
ByteBuffer buffer = ByteBuffer.allocate(32);
buffer.put(new byte[16]);
buffer.flip();
buffer.getInt();
buffer.compact();
int pos = buffer.position();
}
public void viewBuffer() {
ByteBuffer buffer = ByteBuffer.allocate(32);
buffer.putInt(1);
IntBuffer intBuffer = buffer.asIntBuffer();
intBuffer.put(2);
int value = buffer.getInt(); //值为2
}
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
ByteBufferUsage bbu = new ByteBufferUsage();
bbu.useByteBuffer();
bbu.byteOrder();
bbu.compact();
bbu.viewBuffer();
}
}
- filechannel
public class FileChannelUsage {
public void openAndWrite() throws IOException {
FileChannel channel = FileChannel.open(Paths.get("my.txt"), StandardOpenOption.CREATE, StandardOpenOption.WRITE);
ByteBuffer buffer = ByteBuffer.allocate(64);
buffer.putChar(‘A‘).flip();
channel.write(buffer);
}
public void readWriteAbsolute() throws IOException {
FileChannel channel = FileChannel.open(Paths.get("absolute.txt"), StandardOpenOption.READ, StandardOpenOption.CREATE, StandardOpenOption.WRITE);
ByteBuffer writeBuffer = ByteBuffer.allocate(4).putChar(‘A‘).putChar(‘B‘);
writeBuffer.flip();
channel.write(writeBuffer, 1024);
ByteBuffer readBuffer = ByteBuffer.allocate(2);
channel.read(readBuffer, 1026);
readBuffer.flip();
char result = readBuffer.getChar(); //值为‘B‘
}
/**
* @param args the command line arguments
*/
public static void main(String[] args) throws IOException {
FileChannelUsage fcu = new FileChannelUsage();
fcu.openAndWrite();
fcu.readWriteAbsolute();
}
}
6、JSR292与InvokeDynamic
JSR 292: Supporting Dynamically Typed Languages on the JavaTM Platform，支持在JVM上运行动态类型语言。在字节码层面支持了InvokeDynamic。
- 方法句柄MethodHandle
public class ThreadPoolManager {
private final ScheduledExecutorService stpe = Executors
.newScheduledThreadPool(2);
private final BlockingQueue<WorkUnit<String>> lbq;
public ThreadPoolManager(BlockingQueue<WorkUnit<String>> lbq_) {
lbq = lbq_;
}
public ScheduledFuture<?> run(QueueReaderTask msgReader) {
msgReader.setQueue(lbq);
return stpe.scheduleAtFixedRate(msgReader, 10, 10, TimeUnit.MILLISECONDS);
}
private void cancel(final ScheduledFuture<?> hndl) {
stpe.schedule(new Runnable() {
public void run() {
hndl.cancel(true);
}
}, 10, TimeUnit.MILLISECONDS);
}
/**
* 使用传统的反射api
*/
public Method makeReflective() {
Method meth = null;
try {
Class<?>[] argTypes = new Class[]{ScheduledFuture.class};
meth = ThreadPoolManager.class.getDeclaredMethod("cancel", argTypes);
meth.setAccessible(true);
} catch (IllegalArgumentException | NoSuchMethodException
| SecurityException e) {
e.printStackTrace();
}
return meth;
}
/**
* 使用代理类
* @return
*/
public CancelProxy makeProxy() {
return new CancelProxy();
}
/**
* 使用Java7的新api，MethodHandle
* invoke virtual 动态绑定后调用 obj.xxx
* invoke special 静态绑定后调用 super.xxx
* @return
*/
public MethodHandle makeMh() {
MethodHandle mh;
MethodType desc = MethodType.methodType(void.class, ScheduledFuture.class);
try {
mh = MethodHandles.lookup().findVirtual(ThreadPoolManager.class,
"cancel", desc);
} catch (NoSuchMethodException | IllegalAccessException e) {
throw (AssertionError) new AssertionError().initCause(e);
}
return mh;
}
public static class CancelProxy {
private CancelProxy() {
}
public void invoke(ThreadPoolManager mae_, ScheduledFuture<?> hndl_) {
mae_.cancel(hndl_);
}
}
}
- 调用invoke
public class ThreadPoolMain {
/**
* 如果被继承，还能在静态上下文寻找正确的class
*/
private static final Logger logger = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
private ThreadPoolManager manager;
public static void main(String[] args) {
ThreadPoolMain main = new ThreadPoolMain();
main.run();
}
private void cancelUsingReflection(ScheduledFuture<?> hndl) {
Method meth = manager.makeReflective();
try {
System.out.println("With Reflection");
meth.invoke(hndl);
} catch (IllegalAccessException | IllegalArgumentException
| InvocationTargetException e) {
e.printStackTrace();
}
}
private void cancelUsingProxy(ScheduledFuture<?> hndl) {
CancelProxy proxy = manager.makeProxy();
System.out.println("With Proxy");
proxy.invoke(manager, hndl);
}
private void cancelUsingMH(ScheduledFuture<?> hndl) {
MethodHandle mh = manager.makeMh();
try {
System.out.println("With Method Handle");
mh.invokeExact(manager, hndl);
} catch (Throwable e) {
e.printStackTrace();
}
}
private void run() {
BlockingQueue<WorkUnit<String>> lbq = new LinkedBlockingQueue<>();
manager = new ThreadPoolManager(lbq);
final QueueReaderTask msgReader = new QueueReaderTask(100) {
@Override
public void doAction(String msg_) {
if (msg_ != null)
System.out.println("Msg recvd: " + msg_);
}
};
ScheduledFuture<?> hndl = manager.run(msgReader);
cancelUsingMH(hndl);
// cancelUsingProxy(hndl);
// cancelUsingReflection(hndl);
}
}
7、Path接口(重要接口更新)
- Path
public class PathUsage {
public void usePath() {
Path path1 = Paths.get("folder1", "sub1");
Path path2 = Paths.get("folder2", "sub2");
path1.resolve(path2); //folder1\sub1\folder2\sub2
path1.resolveSibling(path2); //folder1\folder2\sub2
path1.relativize(path2); //..\..\folder2\sub2
path1.subpath(0, 1); //folder1
path1.startsWith(path2); //false
path1.endsWith(path2); //false
Paths.get("folder1/./../folder2/my.text").normalize(); //folder2\my.text
}
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
PathUsage usage = new PathUsage();
usage.usePath();
}
}
- DirectoryStream
public class ListFile {
public void listFiles() throws IOException {
Path path = Paths.get("");
try (DirectoryStream<Path> stream = Files.newDirectoryStream(path, "*.*")) {
for (Path entry: stream) {
//使用entry
System.out.println(entry);
}
}
}
/**
* @param args the command line arguments
*/
public static void main(String[] args) throws IOException {
ListFile listFile = new ListFile();
listFile.listFiles();
}
}
- Files
public class FilesUtils {
public void manipulateFiles() throws IOException {
Path newFile = Files.createFile(Paths.get("new.txt").toAbsolutePath());
List<String> content = new ArrayList<String>();
content.add("Hello");
content.add("World");
Files.write(newFile, content, Charset.forName("UTF-8"));
Files.size(newFile);
byte[] bytes = Files.readAllBytes(newFile);
ByteArrayOutputStream output = new ByteArrayOutputStream();
Files.copy(newFile, output);
Files.delete(newFile);
}
/**
* @param args the command line arguments
*/
public static void main(String[] args) throws IOException {
FilesUtils fu = new FilesUtils();
fu.manipulateFiles();
}
}
- WatchService
public class WatchAndCalculate {
public void calculate() throws IOException, InterruptedException {
WatchService service = FileSystems.getDefault().newWatchService();
Path path = Paths.get("").toAbsolutePath();
path.register(service, StandardWatchEventKinds.ENTRY_CREATE);
while (true) {
WatchKey key = service.take();
for (WatchEvent<?> event : key.pollEvents()) {
Path createdPath = (Path) event.context();
createdPath = path.resolve(createdPath);
long size = Files.size(createdPath);
System.out.println(createdPath + " ==> " + size);
}
key.reset();
}
}
/**
* @param args the command line arguments
*/
public static void main(String[] args) throws Throwable {
WatchAndCalculate wc = new WatchAndCalculate();
wc.calculate();
}
}
8、fork/join计算框架
Java7提供的一个用于并行执行任务的框架，是一个把大任务分割成若干个小任务，最终汇总每个小任务结果后得到大任务结果的框架。
该框架为Java8的并行流打下了坚实的基础
原文地址：https://www.cnblogs.com/deityjian/p/11452380.html
时间： 2024-08-04 01:09:04