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![Heap pollution
• 希望編譯器檢查都是 List<String>....
.....: warning: [unchecked] unchecked generic array creation of type java
.util.List<java.lang.String>[] for varargs parameter
Util.doSome(Arrays.asList("three", "four"), Arrays.asList(“five", “six"));
^
1 warning
• 編譯器提醒 doSome() 內部實作可能對每個引數，
只當作 List ...](https://image.slidesharecdn.com/2011oraclejavatwo-jdk7-130208015924-phpapp01/85/Java-SE-7-35-320.jpg)
![Simplified Varargs Method
Invocation
• JDK7...
提醒設計 doSome() 保證不會發生 Heap Pollution
....: warning: [unchecked] Possible heap pollution from parameterized var
arg type T
public static <T> List<T> doSome(T... t) {
^
where T is a type-variable:
T extends Object declared in method <T>doSome(T...)
1 warning](https://image.slidesharecdn.com/2011oraclejavatwo-jdk7-130208015924-phpapp01/85/Java-SE-7-37-320.jpg)
Uploaded byJustin Lin
千呼萬喚始出來的 Java SE 7
文档详细介绍了 Java SE 7 的主要特性和进展，包括 JDK 7 的新功能（如字符串的 switch 语句、二进制字面量、try-with-resources 语句等），以及与并发性相关的更新（如 fork/join 框架）和新引入的 invoke dynamic 指令，展示了 Java 语言及其生态系统的演进。
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千呼萬喚始出來的 Java SE 7
- 1. 千呼萬喚始出來的 Java SE 7 ● 林信良 ● caterpillar@openhome.cc ● http://openhome.cc
- 2. 議程 • Java 進化史 • JSR334 / Coin 專案 • Unicode 6.0.0、JDBC 4.1 • JSR203 / NIO.2 • JSR166y / Concurrency Updates • JSR292 / Da Vinci Machine 專案
- 3. Java 進化史 2002/02/13
- 4. Java 進化史 2004/09/29
- 5. Java 進化史 ？ 2006/12/11
- 6. Java 進化史 2011/07/28 ？
- 7. A / B計畫 • JDK 7 Features updated ! Plan B has apparently been approved – http://www.baptiste-wicht.com/2010/09/jdk-7- features-updated-plan-b-is-apparently-here/
- 8. JDK7 ... λ Jigsaw Language support for collections Annotations on Java types
- 9. JDK7 有... • JDK7 Features – http://openjdk.java.net/projects/jdk7/features/ Concurrency Updates Coin Invoke Dynamic NIO.2
- 10.
- 11. Small language enhancements •Strings in switch • Binary integral literals and underscores in numeric literals • Multi-catch and more precise rethrow • Improved Type Inference for Generic Instance Creation (diamond) • try-with-resources statement • Simplified Varargs Method Invocation
- 12.
- 13.
- 14. 反組譯... 先用 hashCode() 再用 equals()
- 15. Binary integral literalsand underscores in numeric literals • Binary literal • With underscores for clarity
- 16. Multi-catch 略... 都作一樣的事 略...
- 17. Multi-catch • It isa compile-time error if a disjunctive type contains two alternatives Di, Dj where Di is a subtype of Dj.
- 18. Multi-catch • An exceptionparameter whose type is a disjunctive type is implicitly considered to be final. try { /* throws some ReflectiveOperationException */ } catch (final ClassNotFoundException ex1) { /* body */ } catch (final IllegalAccessException ex2) { /* body */ }
- 19. More precise rethrow •JDK6... ... 沒有宣告 Exception ... // 作一些事
- 20. More precise rethrow •JDK7... ... ...
- 21. Inferring Types with<> • 沒有 Generics 前 • 有了 Generics 後 • 有了 Inferring Types 後
- 22. Inferring Types with<> • 僅使用 <> 表示推斷類型 • 不過別什麼都交給編譯器判斷....
- 23. Inferring Types with<> • 如果... • 推斷出來是 Integer 或 Number？
- 24. Inferring Types with<> • 這有什麼問題？
- 25.
- 26.
- 27.
- 28. Try-with-resources try ResourceSpecification Block ⇒ { final VariableModifiers_minus_final R #resource = Expression; Throwable #primaryException = null; try ResourceSpecificationtail Block catch (Throwable #t) { #primaryException = t; throw #t; } finally { if (#resource != null) { if (#primaryException != null) { try { #resource.close(); } catch(Throwable #suppressedException) { #primaryException.addSuppressed(#suppressedException); } } else { #resource.close(); } } } }
- 29.
- 30. Try-with-resources • 如果要處理例外... try-with-resources
- 31. Try-with-resources • API 支援 – java.lang.AutoClosable – java.io.Closeable 繼承 AutoCloseable
- 32. Try-with-resources • API 支援 – java.beans.XMLDecoder – java.beans.XMLEncoder – java.io.Closeable – java.io.ObjectInput – java.io.ObjectOutput – java.sql.Connection – java.sql.ResultSet – java.sql.Statement – java.nio.channels.FileLock – javax.sound.midi.MidiDevice – javax.sound.midi.Receiver – javax.sound.midi.Transmitter – javax.sound.sampled.Line
- 33. Try-with-resources • a 與b 關閉的順序？
- 34. Heap pollution • JDK6.... 要求編譯器檢查傳入引數是不是都是 T 型態 • OK...
- 35. Heap pollution •希望編譯器檢查都是 List<String>.... .....: warning: [unchecked] unchecked generic array creation of type java .util.List<java.lang.String>[] for varargs parameter Util.doSome(Arrays.asList("three", "four"), Arrays.asList(“five", “six")); ^ 1 warning • 編譯器提醒 doSome() 內部實作可能對每個引數， 只當作 List ...
- 36. Heap pollution • 執行時期無法具體確認（reified）引數或變 數型態 – http://en.wikipedia.org/wiki/Heap_pollution • Java 的 Generics 是編譯時期檢查 • Generics 的物件相等性？ – http://caterpillar.onlyfun.net/JavaEssence/Gen ericEquals.html
- 37. Simplified Varargs Method Invocation • JDK7... 提醒設計 doSome() 保證不會發生 Heap Pollution ....: warning: [unchecked] Possible heap pollution from parameterized var arg type T public static <T> List<T> doSome(T... t) { ^ where T is a type-variable: T extends Object declared in method <T>doSome(T...) 1 warning
- 38. Simplified Varargs Method Invocation • @SuppressWarnings(“unchecked”)？ – 連同其它的警訊也抑制了... – 對 API 使用者也是有警訊... • @SafeVarargs • javac -Xlint:varargs;
- 39. Simplified Varargs Method Invocation • JDK7...
- 40. Unicode 6.0.0 • 2010-10-11正式發佈 繪文字（emoji）
- 41. Unicode 6.0.0 • 2010-10-11正式發佈 繪文字（emoji）
- 42. Unicode 6.0.0 • JavaSE 7 – Unicode 5.1.0 Unicode 6.0.0 • Java Tutorial – http://download.oracle.com/javase/tutorial/i18 n/text/unicode.html • Internationalization Enhancements in Java SE 7 – http://download.java.net/jdk7/docs/technotes/ guides/intl/enhancements.7.html
- 43. JDBC 4.1 • 繼承AutoCloseable – Connection – ResultSet – Statement
- 44.
- 45.
- 46. JDBC 4.1 • RowSetProvider java-Djavax.sql.rowset.RowSetFactory=com.sun.rowset.RowSetFactoryImpl • RowSetFactory
- 47.
- 48. NIO2 NIO • File System API • Channels API – Updates to socket channel API – Asynchronous I/O • java.nio – Buffer – Channel – Selector – Charset
- 49. File System API •java.io.File 怎麼了? – Not initially written to be extended – Many of the methods without exceptions – Methods behaved inconsistently across volumes and file systems – Methods for gaining simultaneous metadata about files were inefficient – Developers also requested the ability to develop their own file system implementations, for examples, zip files – ...
- 50. File System API •新套件 – java.nio.file – java.nio.file.attribute • Java Tutorials: File I/O (Featuring NIO.2) – http://download.oracle.com/javase/tutorial/essential/io /fileio.html
- 51. 關於 Path • Methods to access components • Methods to test and compare • Methods to combine paths • File operations • All methods that access file system throw IOException • No other checked exceptions in API
- 52. 關於 Path • 建立Path • 囉嗦點的話...
- 53. 關於 Path • Path操作 同一階層 • 實作 equals() path.equals(otherPath) • 實作 Iterable Path path = ...; for (Path name: path) { System.out.println(name); }
- 54. 檔案移動與複製 • 支援選項設定 –copyTo(target, option...) – moveTo(target, option...)
- 55.
- 56.
- 57. 檔案屬性（Metadata） • 設定群組、擁有者... • 建立Symbolic link、Hard link... • 尋找 Link 的 Target...
- 58. 檔案讀寫 • 針對 java.io的 API
- 59. 檔案讀寫 • 針對 Channels與 ByteBuffers
- 60. 目錄讀取 • 使用 Glob過濾目錄 • What is Glob – http://download.oracle.com/javase/tutorial/essential/io /fileOps.html#glob
- 61.
- 62. FileVisitor 啟始目錄 preVisitDirectory postVisitDirectory 檔案 目錄 鏈結 visitFile visitFile preVisitDirectory postVisitDirectory 檔案 檔案 visitFile visitFile
- 63.
- 64. 新舊之間 • Legacy FileI/O Code – http://download.oracle.com/javase/tutorial/ essential/io/legacy.html
- 65. Asynchronous Channel API •java.nio.channels – AsynchronousSocketChannel – AsynchronousServerSocketChannel – AsynchronousFileChannel – AsynchronousDatagramChannel
- 66. Asynchronous Channel API •建立AsychronousServerSocketChannel – 類似建立ServerSocketChannel並綁定位址 • 接受連結
- 67. Asynchronous Channel API •Future 模式
- 68. Asynchronous Channel API •Future 模式
- 69. Asynchronous Channel API •客戶端建立AsynchronousSocketChannel • 開啟連結 Future<Void>
- 70. Asynchronous Channel API •客戶端傳送訊息 • 伺服端讀取訊息
- 71. Asynchronous Channel API •The asynchronous channel APIs – http://www.ibm.com/developerworks/java/libra ry/j-nio2-1/index.html
- 72. JSR166y / ConcurrencyUpdates
- 73. Concurrency Updates • JDK5 – JSR 166: Concurrency Utilities • JDK7 – JSR166y: Concurrency and collections updates – java.util.concurrent • ForkJoinPool • Phaser • TransferQueue • ConcurrentLinkedDeque • ThreadLocalRandom • ...
- 74.
- 75. Fork / Join模式 • Divide and conquer 的一種實現策略 • 著重在如何切割任務與組合子任務結果
- 76. Fork / Join框架 不需傳回值的子動作 透過泛型傳回值的子任務
- 77. Fork / Join框架 • ForkJoinTask：類似執行緒的輕量級實體 • 有別於 ExecutorService 的 ForkJoinPool – 採用 Work-stealing 演算，讓空閒的執行緒從執行 較慢的執行緒中偷取任務 – 建構與處理器數量相當執行緒，減少頻繁切換負擔
- 78.
- 79.
- 80.
- 81.
- 82. Fibonacci 結果 1134903170 耗時 pick some .... you'd 199604 minimum granularity size for which you always sequentially solve rather than subdividing.
- 83.
- 84.
- 85.
- 86.
- 87. JSR292 / DaVinci Machine 專案
- 88. 靜態定型語言 • 根據資料的型態資訊，將變數及運算式進 行分類，型態資訊是在宣告變數上 • 在執行時期變數的型態資訊無法改變，資 料只能被指定至同一種型態的變數
- 89.
- 90. 靜態定型語言 2: invokestatic #3 // Method doSome:(Ljava/lang/String;)Ljava/lang/Integer; 17: invokevirtual #7 // Method Other.doOther:(Ljava/lang/String;)Ljava/lang/Integer; 32: invokeinterface #9, 2 // InterfaceMethod Another.doAnother:(Ljava/lang/String;)Ljava/lang/Integer;
- 91. 動態定型語言 • 型態資訊在資料本身而不是變數 • 變數本身的型態是在執行時期運算得知， 也同一變數可以參考至各種型態的資料 function max(m, n) { if(n.lessThan(m)) { return m; } JavaScript return n; } def max(m, n): return m if n.lessThan(m) else n Python
- 92. 動態定型語言的挑戰 • 參數與傳回值都沒有型態 • 執行時才提供型態資訊 • 無法提前得知呼叫的方法相關型態資訊 • 如何成功編譯為位元碼（Byte code）？ function max(m, n) { if(n.lessThan(m)) { return m; } return n; }
- 93. 動態定型語言的挑戰 • 為參數與傳回值建立合成（synthetic）類型 – 可符合位元碼對型態的要求 – 需要為各種語言建立特定實作（Implementer）， 以產生對應類型 – JVM 本身的類型（String、Integer...）通常也 無法直接對應 MyObject max(MyObject x, MyObject y) { if(n.lessThan(m)) { return n; invokevirtual #9 // Method MyObject.lessThan:(Ljava/lang/MyObject;)Ljava/lang/Boolean; } return m; }
- 94. 動態定型語言的挑戰 • 運用反射呼叫（reflected invocation） – java.lang.reflect.Method 提供某類別 或介面的方法直接呼叫（正是特定語言實作器 所要求的） – 這些方法仍是執行時期從特定類別上取得 – 執行時期的效能非常不彰
- 95. 動態定型語言的挑戰 • 在 JVM上執行特定語言直譯器（Interpreter） – 非常非常....慢...
- 96. JSR 292 • 為JVM與位元碼中新增invokedynamic指令 invokedynamic <method-specification> <n> • 新的方法連結機制 – java.lang.invoke • CallSite • MethodHandle • ...
- 97. a = 40; • 考慮有個語言... b = a + 2; • 為這段程式碼產生位元碼... bipush 40 the invokedynamic call site is + istore_1 iload_1 invokestatic Method java/lang/Integer.valueOf:"(I)Ljava/lang/Integer;"; bipush 2 invokestatic Method java/lang/Integer.valueOf:"(I)Ljava/lang/Integer;"; invokedynamic InvokeDynamic REF_invokeStatic: Example.mybsm: method implementation currently unknown "(Ljava/lang/invoke/MethodHandles/Lookup; Ljava/lang/String; Ljava/lang/invoke/MethodType;) Ljava/lang/invoke/CallSite;": +: "(Ljava/lang/Integer; bootstrap method Ljava/lang/Integer;) Ljava/lang/Integer;";
- 98. JSR 292 • +對整數的方法實作
- 99. • An invokedynamiccall site is linked to a method by means of a bootstrap method 類似 Reflection？
- 100. JSR 292 • java.lang.reflect.Method – 非方法呼叫專用，執行時期有許多不必要資訊 – 重量級，速度慢 • java.lang.invoke.MethodHandle – 主要目的就是在方法呼叫 – 輕量級，速度快
- 101. JSR 292 • JavaVirtual Machine Support for Non- Java Languages – http://download.java.net/jdk7/docs/technotes/ guides/vm/multiple-language-support.html
- 102. JSR 292 • Ifa programming language was a boat… – http://compsci.ca/blog/if-a-programming- language-was-a-boat/
- 103. 感謝 Orz... ● 林信良 ● caterpillar@openhome.cc ● http://openhome.cc Recently rediscovered diagrams prove Leonardo invented the first JVM？ . http://openjdk.java.net/projects/mlvm/