输出指定小数位数double值

new java.math.BigDecimal(myDoubleValue).setScale(1,java.math.BigDecimal.ROUND_HALF_UP).doubleValue();

其他数字格式：

A pattern of special characters is used to specify the format of the number. This example demonstrates some of the characters. For a complete listing, see the javadoc documentation for the DecimalFormat class. 
There is no symbol that either displays a digit or a blank if no digit present. Hence, it is not possible to format a number so that it will have a specific width. To achieve a specific width, you must manually pad the formatted number. 

    // The 0 symbol shows a digit or 0 if no digit present
    NumberFormat formatter = new DecimalFormat("000000");
    String s = formatter.format(-1234.567);  // -001235
    // notice that the number was rounded up

    // The # symbol shows a digit or nothing if no digit present
    formatter = new DecimalFormat("##");
    s = formatter.format(-1234.567);         // -1235
    s = formatter.format(0);                 // 0
    formatter = new DecimalFormat("##00");
    s = formatter.format(0);                 // 00


    // The . symbol indicates the decimal point
    formatter = new DecimalFormat(".00");
    s = formatter.format(-.567);             // -.57
    formatter = new DecimalFormat("0.00");
    s = formatter.format(-.567);             // -0.57
    formatter = new DecimalFormat("#.#");
    s = formatter.format(-1234.567);         // -1234.6
    formatter = new DecimalFormat("#.######");
    s = formatter.format(-1234.567);         // -1234.567
    formatter = new DecimalFormat(".######");
    s = formatter.format(-1234.567);         // -1234.567
    formatter = new DecimalFormat("#.000000");
    s = formatter.format(-1234.567);         // -1234.567000


    // The , symbol is used to group numbers
    formatter = new DecimalFormat("#,###,###");
    s = formatter.format(-1234.567);         // -1,235
    s = formatter.format(-1234567.890);      // -1,234,568

    // The ; symbol is used to specify an alternate pattern for negative values
    formatter = new DecimalFormat("#;(#)");
    s = formatter.format(-1234.567);         // (1235)

    // The ' symbol is used to quote literal symbols
    formatter = new DecimalFormat("'#'#");
    s = formatter.format(-1234.567);         // -#1235
    formatter = new DecimalFormat("'abc'#");
    s = formatter.format(-1234.567);         // -abc1235