甲骨文发布Java SE 7正式版

7月29日, Java SE 7正式发布! 经过与世界范围内的Java社区, Java平台历时将近五年的协作, 标准版本已经可以下载了.

新特性

改进动态语言支持
改进的IO, 加强对NIO的支持详见 Enhancements in Java I/O
支持非Java语言: Java SE 7 引入一个新的 JVM 指令用于简化实现动态类型编程语言
Garbage-First Collector 新的针对服务器的垃圾收集器用于替换CMS. What is the Garbage-First Collector?
基于ForkJoinPool类的fork/join框架. 适合于多处理器环境下用来进行高效的运行大量任务. 详见 Concurrency Utilities Enhancements in Java SE 7
增强国际化支持. Internationalization Enhancements in Java SE 7

语言特性

二进制数字表达方式

在java7中, 整形(byte, short, int, and long)可以用二进制表示, 加上前缀 0b 或者 0B 就可以了.

	// An 8-bit 'byte' value:
	byte aByte = (byte)0b00100001;

	// A 16-bit 'short' value:
	short aShort = (short)0b1010000101000101;

	// Some 32-bit 'int' values:
	int anInt1 = 0b10100001010001011010000101000101;
	int anInt2 = 0b101;
	int anInt3 = 0B101; // The B can be upper or lower case.

	// A 64-bit 'long' value. Note the "L" suffix:
	long aLong = 0b1010000101000101101000010100010110100001010001011010000101000101L;

view raw binary_literals.java hosted with ❤ by GitHub

switch支持字符串变量

这可是期盼多年的特性. 表达式比较使用 String.equals 方法

	public String getTypeOfDayWithSwitchStatement(String dayOfWeekArg) {
	String typeOfDay;
	switch (dayOfWeekArg) {
	case "Monday":
	typeOfDay = "Start of work week";
	break;
	case "Tuesday":
	case "Wednesday":
	case "Thursday":
	typeOfDay = "Midweek";
	break;
	case "Friday":
	typeOfDay = "End of work week";
	break;
	case "Saturday":
	case "Sunday":
	typeOfDay = "Weekend";
	break;
	default:
	throw new IllegalArgumentException("Invalid day of the week: " + dayOfWeekArg);
	}
	return typeOfDay;
	}

view raw strings_in_switch_statements.java hosted with ❤ by GitHub

try-with-resources 语句

在资源使用完后自动关闭. 资源是指实现了 java.lang.AutoCloseable 或者 Closeable 接口的类.\ 注意在try-with-resources中依然可以使用 catch 和 finally, catch 和 finally 会在资源关闭之后运行.

	public static void viewTable(Connection con) throws SQLException {

	String query = "select COF_NAME, SUP_ID, PRICE, SALES, TOTAL from COFFEES";

	try (Statement stmt = con.createStatement()) {

	ResultSet rs = stmt.executeQuery(query);

	while (rs.next()) {
	String coffeeName = rs.getString("COF_NAME");
	int supplierID = rs.getInt("SUP_ID");
	float price = rs.getFloat("PRICE");
	int sales = rs.getInt("SALES");
	int total = rs.getInt("TOTAL");
	System.out.println(coffeeName + ", " + supplierID + ", " + price +
	", " + sales + ", " + total);
	}

	} catch (SQLException e) {
	JDBCTutorialUtilities.printSQLException(e);
	}
	}

view raw try-with-resources.java hosted with ❤ by GitHub

同时捕获多个异常

catch (IOException|SQLException ex) { logger.log(ex); throw ex; }

数字表达中使用下划线

	//正确
	long creditCardNumber = 1234_5678_9012_3456L;
	long socialSecurityNumber = 999_99_9999L;
	float pi = 3.14_15F;
	long hexBytes = 0xFF_EC_DE_5E;
	long hexWords = 0xCAFE_BABE;
	long maxLong = 0x7fff_ffff_ffff_ffffL;
	byte nybbles = 0b0010_0101;
	long bytes = 0b11010010_01101001_10010100_10010010;

	//错误
	float pi1 = 3_.1415F; // Invalid; cannot put underscores adjacent to a decimal point
	float pi2 = 3._1415F; // Invalid; cannot put underscores adjacent to a decimal point
	long socialSecurityNumber1 = 999_99_9999_L; // Invalid; cannot put underscores prior to an L suffix
	int x3 = 52_; // Invalid; cannot put underscores at the end of a literal
	int x4 = 5_______2; // OK (decimal literal)
	int x5 = 0_x52; // Invalid; cannot put underscores in the 0x radix prefix
	int x6 = 0x_52; // Invalid; cannot put underscores at the beginning of a number
	int x7 = 0x5_2; // OK (hexadecimal literal)
	int x8 = 0x52_; // Invalid; cannot put underscores at the end of a number
	int x11 = 052_; // Invalid; cannot put underscores at the end of a number

view raw underscores_in_numeric_literals.java hosted with ❤ by GitHub

泛型在创建实例时的类型引用

之前的代码 Map<String, List<String>> myMap = new HashMap<String, List<String>>(); Java7的代码 Map<String, List<String>> myMap = new HashMap<>(); 编译器可以根据声明自动推断范型的类型.

Improved Compiler Warnings and Errors When Using Non-Reifiable Formal Parameters with Varargs Methods

详细: 链接

可惜那个很酷的集合声明语法没有实现 List<String> people = {"Frank", "Mary", "Satan"}; Map<String, Integer> map = {"key" : 1}; 是不是有些动态语言的味道

闭包也没有, 可惜…