前言

之前學習的過程中，每天都是老師說這個是JDK7以后可以使用，那個是JDK8以后可以使用，每天都記的很混亂，今天專門忙里偷閑，歸攏整理下JDK7的新特性，對于JDK的新特性，后期會進行整理更新，希望可以幫助到有需要的朋友。

一，語法上

1.1switch中可以使用字串了

String s = "test";

switch (s) {

case "test" :

System.out.println("test");

case "test1" :

System.out.println("test1");

break ;

default :

System.out.println("break");

break ;

}

1.2二進制變量的表示,支持將整數類型用二進制來表示，用0b開頭。

// 所有整數 int， short，long，byte都可以用二進制表示

// An 8-bit 'byte' value:

byte aByte = (byte) 0b00100001;

// A 16-bit 'short' value:

short aShort = (short) 0b1010000101000101;

// Some 32-bit 'int' values:

intanInt1 = 0b10100001010001011010000101000101;

intanInt2 = 0b101;

intanInt3 = 0B101; // The B can be upper or lower case.

// A 64-bit 'long' value. Note the "L" suffix:

long aLong =

0b1010000101000101101000010100010110100001010001011010000101000101L;

// 二進制在數組等的使用

final int[] phases = { 0b00110001, 0b01100010, 0b11000100, 0b10001001,0b00010011, 0b00100110, 0b01001100, 0b10011000 };

1.3 Try-with-resource語句

注意：實現java.lang.AutoCloseable接口的資源都可以放到try中，跟final里面的關閉資源類似； 按照聲明逆序關閉資源 ;Try塊拋出的異常通過Throwable.getSuppressed獲取

try (java.util.zip.ZipFile zf = new java.util.zip.ZipFile(zipFileName);

java.io.BufferedWriter writer = java.nio.file.Files.newBufferedWriter(outputFilePath, charset)) {

// Enumerate each entry

for (java.util.Enumeration entries = zf.entries(); entries.hasMoreElements()) {

// Get the entry name and write it to the output file

String newLine = System.getProperty("line.separator");

String zipEntryName = ((java.util.zip.ZipEntry) entries

.nextElement()).getName() + newLine;

writer.write(zipEntryName, 0, zipEntryName.length());

}

}

}

1.4 Catch多個異常 說明：Catch異常類型為final； 生成Bytecode 會比多個catch小； Rethrow時保持異常類型

public static void main(String[] args) throws Exception {

try {

testthrows();

} catch (IOException | SQLException ex) {

throw ex;

}

}

public static void testthrows() throws IOException, SQLException {}

1.5 數字類型的下劃線表示 更友好的表示方式，不過要注意下劃線添加的一些標準，可以參考下面的示例

long creditCardNumber = 1234_5678_9012_3456L;

long socialSecurityNumber = 999_99_9999L;

float pi = 3.14_15F;

long hexBytes = 0xFF_EC_DE_5E;

long hexWords = 0xCAFE_BABE;

long maxLong = 0x7fff_ffff_ffff_ffffL;

byte nybbles = 0b0010_0101;

long bytes = 0b11010010_01101001_10010100_10010010;

//float pi1 = 3_.1415F;// Invalid; cannot put underscores adjacent to a decimal point

//float pi2 = 3._1415F;// Invalid; cannot put underscores adjacent to a decimal point

//long socialSecurityNumber1= 999_99_9999_L;// Invalid; cannot put underscores prior to an L suffix

//int x1 = _52;// This is an identifier, not a numeric literal

int x2 = 5_2;// OK (decimal literal)

//int x3 = 52_;// Invalid; cannot put underscores at the end of a literal

int x4 = 52;// OK (decimal literal)

//int x5 = 0_x52;// Invalid; cannot put underscores in the 0x radix prefix

//int x6 = 0x_52;// Invalid; cannot put underscores at the beginning of a number

int x7 = 0x5_2;// OK (hexadecimal literal)

//int x8 = 0x52_;// Invalid; cannot put underscores at the end of a number

int x9 = 0_52; // OK (octal literal)

int x10 = 05_2;// OK (octal literal)

//int x11 = 052_;// Invalid; cannot put underscores at the end of a number

1.6 泛型實例的創建可以通過類型推斷來簡化 可以去掉后面new部分的泛型類型，只用<>就可以了。

//使用泛型前

List strList = new ArrayList();

List strList4 = new ArrayList();

List>> strList5 = new ArrayList>>();

//編譯器使用尖括號 (<>) 推斷類型

List strList0 = new ArrayList();

List>> strList1 = new ArrayList>>();

List strList2 = new ArrayList<>();

List>> strList3 = new ArrayList<>();

List list = new ArrayList<>();

list.add("A");

// The following statement should fail since addAll expects

// Collection extends String>

//list.addAll(new ArrayList<>());

1.7在可變參數方法中傳遞非具體化參數,改進編譯警告和錯誤

Heap pollution 指一個變量被指向另外一個不是相同類型的變量。例如

List l = new ArrayList();

List ls = l; // unchecked warning

l.add(0, new Integer(42)); // another unchecked warning

String s = ls.get(0); // ClassCastException is thrown

Jdk7:

public static void addToList (List listArg, T... elements) {

for (T x : elements) {

listArg.add(x);

}

}

你會得到一個warning

warning: [varargs] Possible heap pollution from parameterized vararg type

要消除警告，可以有三種方式

1.加 annotation @SafeVarargs

2.加 annotation @SuppressWarnings({"unchecked", "varargs"})

3.使用編譯器參數 –Xlint:varargs;

1.8 信息更豐富的回溯追蹤 就是上面try中try語句和里面的語句同時拋出異常時，異常棧的信息

java.io.IOException at Suppress.write(Suppress.java:19)at Suppress.main(Suppress.java:8)

Suppressed: java.io.IOException at Suppress.close(Suppress.java:24)

at Suppress.main(Suppress.java:9)

Suppressed: java.io.IOException at Suppress.close(Suppress.java:24)

at Suppress.main(Suppress.java:9)

二、NIO2的一些新特性

java.nio.file 和java.nio.file.attribute包 支持更詳細屬性，比如權限，所有者

symbolic and hard links支持

Path訪問文件系統，Files支持各種文件操作

高效的訪問metadata信息

遞歸查找文件樹，文件擴展搜索

文件系統修改通知機制

File類操作API兼容

文件隨機訪問增強 mapping a region,locl a region,絕對位置讀取

AIO Reactor(基于事件)和Proactor

下面列一些示例：

2.1 IO and New IO 監聽文件系統變化通知

通過FileSystems.getDefault().newWatchService()獲取watchService，然后將需要監聽的path目錄注冊到這個watchservice中，對于這個目錄的文件修改，新增，刪除等實踐可以配置，然后就自動能監聽到響應的事件。

private WatchService watcher;

public TestWatcherService(Path path) throws IOException {

watcher = FileSystems.getDefault().newWatchService();

path.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);

}

public void handleEvents() throws InterruptedException {

while (true) {

WatchKey key = watcher.take();

for (WatchEvent> event : key.pollEvents()) {

WatchEvent.Kind kind = event.kind();

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;

}

2.2 IO and New IO遍歷文件樹，通過繼承SimpleFileVisitor類，實現事件遍歷目錄樹操作，然后通過Files.walkFileTree(listDir, opts,Integer.MAX_VALUE, walk);這個API來遍歷目錄樹

private void workFilePath() {

Path listDir = Paths.get("/tmp"); // define the starting file

ListTree walk = new ListTree();

Files.walkFileTree(listDir, walk);

// 遍歷的時候跟蹤鏈接

EnumSet opts = EnumSet.of(FileVisitOption.FOLLOW_LINKS);

try {

Files.walkFileTree(listDir, opts, Integer.MAX_VALUE, walk);

} catch (IOException e) {

System.err.println(e);

}

class ListTree extends SimpleFileVisitor {// NIO2 遞歸遍歷文件目錄的接口

@Override

public FileVisitResult postVisitDirectory(Path dir, IOException exc) {

System.out.println("Visited directory: " + dir.toString());

return FileVisitResult.CONTINUE;

}

@Override

public FileVisitResult visitFileFailed(Path file, IOException exc) {

System.out.println(exc);

return FileVisitResult.CONTINUE;

}

}

2.3 AIO異步IO 文件和網絡 異步IO在java

NIO2實現了，都是用AsynchronousFileChannel，AsynchronousSocketChanne等實現，關于同步阻塞IO，同步非阻塞IO，異步阻塞IO和異步非阻塞IO在ppt的這頁上下面備注有說明，有興趣的可以深入了解下。Java NIO2中就實現了操作系統的異步非阻塞IO。

// 使用AsynchronousFileChannel.open(path, withOptions(),taskExecutor))這個API對異步文件IO的處理

public static void asyFileChannel2() {

final int THREADS = 5;

ExecutorService taskExecutor = Executors.newFixedThreadPool(THREADS);

String encoding = System.getProperty("file.encoding");

List> list = new ArrayList<>();

int sheeps = 0;

Path path = Paths.get("/tmp","store.txt");

try (AsynchronousFileChannel asynchronousFileChannel = AsynchronousFileChannel.open(path, withOptions(), taskExecutor)) {

for (int i = 0; i < 50; i++) {

Callable worker = new Callable(){

@Override

public ByteBuffer call() throws Exception {

ByteBuffer buffer = ByteBuffer.allocateDirect(ThreadLocalRandom.current().nextInt(100, 200));

asynchronousFileChannel.read(buffer, ThreadLocalRandom)

……

三. JDBC 4.1

3.1.可以使用try-with-resources自動關閉Connection, ResultSet, 和 Statement資源對象

3.2. RowSet 1.1：引入RowSetFactory接口和RowSetProvider類，可以創建JDBC driver支持的各種 row sets，這里的rowset實現其實就是將sql語句上的一些操作轉為方法的操作，封裝了一些功能。

3.3. JDBC-ODBC驅動會在jdk8中刪除

try (Statement stmt = con.createStatement()) {

RowSetFactory aFactory = RowSetProvider.newFactory();

CachedRowSet crs = aFactory.createCachedRowSet();

RowSetFactory rsf = RowSetProvider.newFactory("com.sun.rowset.RowSetFactoryImpl", null);

WebRowSet wrs = rsf.createWebRowSet();

createCachedRowSet

createFilteredRowSet

createJdbcRowSet

createJoinRowSet

createWebRowSet

}

四、并發工具增強

4.1.fork-join

最大的增強，充分利用多核特性，將大問題分解成各個子問題，由多個cpu可以同時解決多個子問題，最后合并結果，繼承RecursiveTask，實現compute方法，然后調用fork計算，最后用join合并結果。

class Fibonacci extends RecursiveTask {

final int n;

Fibonacci(int n) {

this.n = n;

}

private int compute(int small) {

final int[] results = { 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89 };

return results[small];

}

public Integer compute() {

if (n <= 10) {

return compute(n);

}

Fibonacci f1 = new Fibonacci(n - 1);

Fibonacci f2 = new Fibonacci(n - 2);

System.out.println("fork new thread for " + (n - 1));

f1.fork();

System.out.println("fork new thread for " + (n - 2));

f2.fork();

return f1.join() + f2.join();

}

}

4.2.ThreadLocalRandon 并發下隨機數生成類，保證并發下的隨機數生成的線程安全，實際上就是使用threadlocal

final int MAX = 100000;

ThreadLocalRandom threadLocalRandom = ThreadLocalRandom.current();

long start = System.nanoTime();

for (int i = 0; i < MAX; i++) {

threadLocalRandom.nextDouble();

}

long end = System.nanoTime() - start;

System.out.println("use time1 : " + end);

long start2 = System.nanoTime();

for (int i = 0; i < MAX; i++) {

Math.random();

}

long end2 = System.nanoTime() - start2;

System.out.println("use time2 : " + end2);

4.3. phaser 類似cyclebarrier和countdownlatch，不過可以動態添加資源減少資源

void runTasks(List tasks) {

final Phaser phaser = new Phaser(1); // "1" to register self

// create and start threads

for (final Runnable task : tasks) {

phaser.register();

new Thread() {

public void run() {

phaser.arriveAndAwaitAdvance(); // await all creation

task.run();

}

}.start();

}

// allow threads to start and deregister self

phaser.arriveAndDeregister();

}

結尾

由于個人能力問題，還有很多需要改進的地方，如有錯誤，煩請各位大佬私信或留言進行批評指正，在下定當及時更正！

總結

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