JDK6 to JDK7 => API Enhancements

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.

Reference

Enhancements in Java SE 7
Java Language Enhancements

Points

1. 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");
     }
    }
    
    
   }
   

2. 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<>();
     }
     
   }
   

3. 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);
           }
       }
       
   }
   

4. 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 {}
       
   }
   

5.