JDK5特性简介

新项目要用JDK5.0，所以简单的在网上查了查，具体开发时，一点点研究

我会把心得狂帖

JDK5.0新特性简介

一 从xml中装载属性

 

格式：

<properties> <comment>Hi</comment> <entry key="id">1</entry> <entry key="name">rocie</entry> <entry key="email">rocie@sina.com</entry> </properties>

 

 

通过以下方法加载：

Properties prop = new Properties(); FileInputStream fis =  new FileInputStream("d:/jdk5/properties/test.xml"); prop.loadFromXML(fis); prop.list(System.out); System.out.println("Name: " + prop.getProperty("name"));

 

 

将xml文件放在WEB-INF/classes/目录下，可以防止对路径的硬编码

InputStream is = PropertiesTest.class.getClassLoader().getResourceAsStream("rocie.xml"); Properties ps = new Properties(); ps.loadFromXML(is); System.out.println("name:"+ps.getProperty("name"));

 

 

通过以下方法保存：

Properties prop = new Properties(); prop.setProperty("id", "2"); prop.setProperty("name", "彭大双"); prop.setProperty("email", "pds@dotraining.com"); FileOutputStream fos = new FileOutputStream("d:/jdk5/properties/pds.xml"); prop.storeToXML(fos, "彭大双","gbk"); fos.close();

 

 

xml文件细节：

<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd"> <properties> <comment>Hi</comment> <entry key="id">1</entry> <entry key="name">rocie</entry> <entry key="email">rocie@sina.com</entry> </properties>

 

 

DTD文件：

<?xml version="1.0" encoding="UTF-8"?> <!-- DTD for properties --> <!ELEMENT properties ( comment?, entry* ) > <!ATTLIST properties version CDATA #FIXED "1.0"> <!ELEMENT comment (#PCDATA) > <!ELEMENT entry (#PCDATA) > <!ATTLIST entry key CDATA #REQUIRED>

注：?表示0或1；*表示0至无限；+表示至少一个

 

 

二 并发集合

问题：ConcurrentModificationException、fail-fast

 

当遍历一个Iterator时，如果该Iterator对应的List里的元素发生改变，则抛出这个异常。

解决方法：java.util.concurrent

 

用CopyOnWriteArrayList代替原来的ArrayList

copy-on-write:这意味着如果有大量的读（即 get() ） 和迭代，不必同步操作以照顾偶尔的写（即 add() ）调用。对于新的 CopyOnWriteArrayList 和 CopyOnWriteArraySet 类，所有可变的（mutable）操作都首先取得后台数组的副本，对副本进行更改，然后替换副本。这种做法保证了在遍历自身更改的集合时，永远不会抛出 ConcurrentModificationException 。遍历集合会用原来的集合完成，而在以后的操作中使用更新后的集合。

 

 

三用 for/in 在 Java 5.0 中增强循环

public static List<Integer> list = new ArrayList<Integer>();               public static int[] is = new int[]{1,2,3,4,65,456};               static        {                          for(int i=0;i<100;i++)                      list.add(i);                     }               public static void main(String args[])        {               for(Integer i:list)                      System.out.println(i);                   System.out.println("-------other for each--------");               for(int i:is)                      System.out.println(i);        }

四枚举类型 enum

public class EnumTest {        private Color color;               public static enum Color {red,yellow,blue,green};                   public Color getColor() {               return color;        }            public void setColor(Color color) {               this.color = color;        }            public static void main(String args[])        {               for(Color c:Color.values())               {                      System.out.println("name:"+c.name()+"ordinal:"+c.ordinal());               }                   EnumTest et = new EnumTest();               et.setColor(Color.red);               Color c = et.getColor();               switch(c)               {               case red: System.out.println("red:"+c.name()+c.ordinal());                                    break;               case yellow: System.out.println("yellow"+c.name()+c.ordinal());                                    break;               default : System.out.println("over");               }                      } }

 

 

五使用泛型 Generics types

定义简单的泛型   public static void main(String args[]) { List<String> list = new ArrayList<String>();                      for(int i=0;i<100;i++)               list.add(String.valueOf(i));                      String five = list.get(4);                       }

使用通配符   public abstract class Shape {   public abstract void draw(Canvas c);   }   public class Circle extends Shape { private int x, y, radius;   public void draw(Canvas c) { ... }   }   public class Rectangle extends Shape { private int x, y, width, height;   public void draw(Canvas c) { ... }   }       public class Canvas {       public void draw2All(List<? extends Shape> shapes)       {              for (Shape s: shapes)                     s.draw(this);       }           public static void main(String args[])       {              List<Shape> list = new ArrayList<Shape>();              list.add(new Circle());              list.add(new Rectangle());              new Canvas().draw2All(list);       }   }

泛形方法          public static <T> void fromArrayToCollection(T[] a, Collection<T> c)          {                 for (T o : a)                        c.add(o);                                 for(T o:c)                        System.out.println(o);          }                        public static void main(String args[])          {                 String[] as = new String[]{"1s","2s","3s","4s"};                 List<String> list = new ArrayList<String>();                 fromArrayToCollection(as,list);                                             Integer[] is = new Integer[]{new Integer(1),new Integer(2),new Integer(3)};                 List<Integer> li = new ArrayList<Integer>();                 fromArrayToCollection(is,li);                  }

 

 

六自动拆/装箱 Autoboxing/Unboxing

public static void main(String args[]) {               List<Integer> list = new ArrayList<Integer>();               for(int i=0;i<100;i++)                      list.add(i);                     }