我們知道double類型在進行處理時會涉及到精度丟失問題比如 double d=100*1.005; 結果d的結果為100.49999999999999 怎麼解決這種問題呢，用DecimalFormat，它對double類型的進行四捨五入處理用法如下： DecimalFormat df=new DecimalFormat(pattern); String nums=df.format(value); 這裡給pattern：”.00“ value:100*1.005 nums值為：100.50 pattern常用的千分號顯示：#,##0.00 (為什麼個位數用0不用#，因為如果df.format(0)，用#的話0顯示為空，結果為.00而用0的話顯示0.00) pattern設置可以參考下面： Symbol Location Localized? Meaning 0 Number Yes Digit # Number Yes Digit, zero shows as absent . Number Yes Decimal separator or monetary decimal separator - Number Yes Minus sign , Number Yes Grouping separator E Number Yes Separates mantissa and exponent in scientific notation. Need not be quoted in prefix or suffix. ; Subpattern boundary Yes Separates positive and negative subpatterns % Prefix or suffix Yes Multiply by 100 and show as percentage \u2030 Prefix or suffix Yes Multiply by 1000 and show as per mille ¤(\u00A4) Prefix or suffix No Currency sign, replaced by currency symbol. If doubled, replaced by international currency symbol. If present in a pattern, the monetary decimal separator is used instead of the decimal separator. ' Prefix or suffix No Used to quote special characters in a prefix or suffix, for example, "'#'#" formats 123 to "#123". To create a single quote itself, use two in a row: "# o''clock".
