Java 7的主要变化http://code.joejag.com/2009/new-language-features-in-java-7/

1.对collections的支持

 

Java代码

1. List<String> list = new ArrayList<String>();   
2. list.add("item");   
3. String item = list.get(0);   
4.   
5. Set<String> set = new HashSet<String>();   
6. set.add("item");   
7.   
8. Map<String, Integer> map = new HashMap<String, Integer>();   
9. map.put("key", 1);   
10. int value = map.get("key");  

List<String> list = new ArrayList<String>();list.add("item");String item = list.get(0);Set<String> set = new HashSet<String>();set.add("item");Map<String, Integer> map = new HashMap<String, Integer>();map.put("key", 1);int value = map.get("key");

 现在你还可以：

 

Java代码

1. List<String> list = ["item"];   
2. String item = list[0];   
3.   
4. Set<String> set = {"item"};   
5.   
6. Map<String, Integer> map = {"key" : 1};   
7. int value = map["key"];  

List<String> list = ["item"];String item = list[0];Set<String> set = {"item"};Map<String, Integer> map = {"key" : 1};int value = map["key"];

 

 

2.自动资源管理

 

Java代码

1. BufferedReader br = new BufferedReader(new FileReader(path));   
2. try {   
3.    return br.readLine();   
4. } finally {   
5.    br.close();   
6. }  

BufferedReader br = new BufferedReader(new FileReader(path));try {   return br.readLine();} finally {   br.close();}

 becomes:

 

Java代码

1. try (BufferedReader br = new BufferedReader(new FileReader(path)) {   
2.    return br.readLine();   
3. }   
4.   
5. You can declare more than one resource to close:   
6.   
7. try (   
8.    InputStream in = new FileInputStream(src);   
9.    OutputStream out = new FileOutputStream(dest))   
10. {   
11.  // code   
12. }  

try (BufferedReader br = new BufferedReader(new FileReader(path)) {   return br.readLine();}You can declare more than one resource to close:try (   InputStream in = new FileInputStream(src);   OutputStream out = new FileOutputStream(dest)){ // code}

 

3.对通用实例创建(diamond)的type引用进行了改进

 

 

Java代码

1. Map<String, List<String>> anagrams = new HashMap<String, List<String>>();  

Map<String, List<String>> anagrams = new HashMap<String, List<String>>();

 becomes:

 

Java代码

1. Map<String, List<String>> anagrams = new HashMap<>();  

Map<String, List<String>> anagrams = new HashMap<>();

4.数值可加下划线

 

Java代码

1. int one_million = 1_000_000;  

int one_million = 1_000_000;

  

5.在switch中可使用string

 

Java代码

1. String s = ...   
2. switch(s) {   
3.  case "quux":   
4.     processQuux(s);   
5.     // fall-through   
6.   
7.   case "foo":   
8.   case "bar":   
9.     processFooOrBar(s);   
10.     break;   
11.   
12.   case "baz":   
13.      processBaz(s);   
14.     // fall-through   
15.   
16.   default:   
17.     processDefault(s);   
18.     break;   
19. }  

String s = ...switch(s) { case "quux":    processQuux(s);    // fall-through  case "foo":  case "bar":    processFooOrBar(s);    break;  case "baz":     processBaz(s);    // fall-through  default:    processDefault(s);    break;}

 

6.二进制文字

 

Java代码

1. int binary = 0b1001_1001;  

int binary = 0b1001_1001;

  

7.简化了可变参数方法的调用

 

当程序员试图使用一个不可具体化的可变参数并调用一个*varargs* （可变）方法时，编辑器会生成一个“非安全操作”的警告

 

 

 

Here are 7 of the new features that have been completed:

• Language support for collections
• Automatic Resource Management
• Improved Type Inference for Generic Instance Creation (diamond)
• Underscores in numeric literals
• Strings in switch
• Binary literals
• Simplified Varargs Method Invocation

There is a lot more to Java 7 then just these language changes. I’ll be exploring the rest of the release in future posts. One of the big debates is currently around Closures, which are a separate JSR.

Language support for collections

Java will be getting first class language support for creating collections. The style change means that collections can be created like they are in Ruby, Perl etc.

Instead of:

List<String> list = new ArrayList<String>();list.add("item");String item = list.get(0);Set<String> set = new HashSet<String>();set.add("item");Map<String, Integer> map = new HashMap<String, Integer>();map.put("key", 1);int value = map.get("key");

You will be able to use:

List<String> list = ["item"];String item = list[0];Set<String> set = {"item"};Map<String, Integer> map = {"key" : 1};int value = map["key"];

These collections are immutable.

Automatic Resource Management

Some resources in Java need to be closed manually like InputStream, Writers, Sockets, Sql classes. This language feature allows the try statement itself to declare one of more resources. These resources are scoped to the try block and are closed automatically.

This:

BufferedReader br = new BufferedReader(new FileReader(path));try {   return br.readLine();} finally {   br.close();}

becomes:

try (BufferedReader br = new BufferedReader(new FileReader(path)) {   return br.readLine();}

You can declare more than one resource to close:

try (   InputStream in = new FileInputStream(src);   OutputStream out = new FileOutputStream(dest)){ // code}

To support this behaviour all closable classes will be retro-fitted to implement a Closable interface.

Improved Type Inference for Generic Instance Creation (diamond)

This is a particular annoyance which is best served with an example:

Map<String, List<String>> anagrams = new HashMap<String, List<String>>();

becomes:

Map<String, List<String>> anagrams = new HashMap<>();

This is called the diamond operator: <> which infers the type from the reference declaration.

Underscores in numeric literals

Long numbers are hard to read. You can now split them up using an underscore in ints and longs:

int one_million = 1_000_000;

Strings in switch

Currently you can only use numbers or enums in switch statements. String has been added as a candidate:

String s = ...switch(s) { case "quux":    processQuux(s);    // fall-through  case "foo":  case "bar":    processFooOrBar(s);    break;  case "baz":     processBaz(s);    // fall-through  default:    processDefault(s);    break;}

Binary literals

Java code, due to its C heritage, has traditionally forced programmers to represent numbers in only decimal, octal, or hexadecimal.

As quite a few domains are bit orientated, this restriction can introduce errors. You can now create binary numbers using an 0b prefix.

int binary = 0b1001_1001;

Simplified Varargs Method Invocation

When a programmer tries to invoke a *varargs* (variable arity) method with a non-reifiable varargs type, the compiler currently generates an “unsafe operation” warning. JDK 7 moves the warning from the call site to the method declaration. This will enable API designers to use varargs due to the reduction of warnings reported.