Description
打算把系統的執行環境從 JDK6 升級到 JDK7, 整理一下有哪些可用.
比較期待的部分是語法, NIO2, G1. 這頁是整理語法的部分.
比較期待的部分是語法, NIO2, G1. 這頁是整理語法的部分.
Reference
Points
- Strings in switch Statements
package test; public class TestStringSwitch { public static void main(String[] params) { inJDK7("abc"); inJDK6("abc"); } private static void inJDK7(String txt) { switch (txt) { case "a": System.out.println("a"); break; case "b": System.out.println("b"); break; case "abc": System.out.println("abc"); break; default: System.out.println("not match"); } } private static void inJDK6(String txt) { if ( "a".equals(txt) ) { System.out.println("a"); } else if ( "b".equals(txt) ) { System.out.println("b"); } else if ( "abc".equals(txt) ) { System.out.println("abc"); } else { System.out.println("not match"); } } } - Type Inference for Generic Instance Creation
package test; import java.util.HashMap; import java.util.List; import java.util.Map; public class TestGenericDeclare { public static void main(String[] params) { // JDK6 Map> map0 = new HashMap >(); // JDK7 Map > map1 = new HashMap<>(); } } - The try-with-resources Statement
試用後可以看到這個語法可以讓程式簡化很多.package test; import java.io.BufferedReader; import java.io.File; import java.io.FileReader; import java.io.IOException; import java.io.Reader; public class TestAutoClosable { public static void main(String[] params) throws IOException { File file1 = new File("d:/test.txt"); File file2 = new File("d:/test2.txt"); inJDK6(file1,file2); inJDK7(file1,file2); } private static void inJDK7(File file1, File file2) throws IOException { try ( FileReader fileReader1 = new FileReader(file1); FileReader fileReader2 = new FileReader(file2); BufferedReader reader1 = new MyBufferedReader("7 reader1", fileReader1); BufferedReader reader2 = new MyBufferedReader("7 reader2", fileReader2); ) { System.out.println(reader1.readLine()); System.out.println(reader2.readLine()); } } private static void inJDK6(File file1, File file2) { BufferedReader reader1 = null; BufferedReader reader2 = null; try { reader1 = new MyBufferedReader("JDK6 style reader1", new FileReader(file1)); reader2 = new MyBufferedReader("JDK6 style reader2", new FileReader(file2)); System.out.println(reader1.readLine()); System.out.println(reader2.readLine()); } catch(Throwable ex) { ex.printStackTrace(); } finally { if ( reader1 != null ) { try { reader1.close(); } catch (IOException e) { e.printStackTrace(); } } if ( reader2 != null ) { try { reader2.close(); } catch (IOException e) { e.printStackTrace(); } } } } private static class MyBufferedReader extends BufferedReader { private final String name; public MyBufferedReader(String name, Reader reader) { super(reader); this.name = name; } @Override public void close() throws IOException { super.close(); System.out.println("close " + name); } } } - Catching Multiple Exception Types and Rethrowing Exceptions with Improved Type Checking
有時對於不特別處理的 checked exception 動作也只是往外丟, 在 JDK7 之前需要在 method 上特別註明這個 checked exception, 但 JDK7 之後, 沒有特別需要的, 直接往外丟的 exception 就算沒有在 method 上宣告, compiler 也不會判你錯.
package test; public class TestHandleMoreThanOneException { public static void main(String[] params) throws Exception { rethrowEx("3"); } private static void rethrowEx(String exNum) throws Ex1,Ex2 { try { throwEx(exNum); } catch (Ex1 | Ex2 e) { throw e; } catch (Exception e) { throw e; } } private static void throwEx(String exNum) throws Ex1, Ex2 { switch (exNum) { case "1": throw new Ex1(); case "2": throw new Ex2(); default: System.out.println("not match"); } } public static class Ex1 extends Exception {} public static class Ex2 extends Exception {} }
