Java 7语言的新特性

1. 新的二进制数字的表达方式
如下面的二进制数常量

byte b = (byte)0b00010011;
short s = (byte)0b001000000000000;

2. 使用下划线对数字进行分隔

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

非法的使用方式

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;

3. Switch语句支持字符串变量

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;
}

4.泛型实例创建时的类型推断

//Java 7之前
Map<String, List<String>> myMap = new HashMap<String, List<String>>();

//Java 7
Map<String, List<String>> myMap = new HashMap<>();

<>符号是必须的。


5. 改进了使用可变参数时的编译器的错误和警告信息。


6. try-with-resources语句

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);
    }
  }

7. 捕获多个异常，并重新抛出改进类型的异常。

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