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java中的格式化输出（类似C语言的printf）

　2008-01-05 19:29:38　来源：WEB开发网　　　

核心提示：　　前几天想在java中用格式化输出，多亏rollingpig、zlzj2010等几位老大提示，java中的格式化输出（类似C语言的printf），现在我用text package中的NumberFormat和DecimalFomat实现了一把，给大家show一下

　　前几天想在java中用格式化输出，多亏rollingpig、zlzj2010等几位老大提示，现在我用text package中的NumberFormat和DecimalFomat实现了一把，给大家show一下，请多指教。

　　简单说明：

　　a.格式描述符:

　　1. L或l －使数字左对齐（缺省是右对齐）
　　2. C或c －使数字居中对齐（缺省是右对齐）
　　3. X或x －显示数字为十六进制（缺省是十进制）
　　4. B或b －显示数字为八进制（缺省是十进制）
　　5. ,（半角逗号）－千位分隔符
　　6. S或s －显示数字为科学记数法
　　7. Z或z －用零填空位（缺省是空格）
　　8. w.d （两个整数用半角句号隔开）－指定输出域宽及精度

　　b. "fillChar"是填空位符（缺省为空格）
　　－－你可以用MyOut.fillChar = '*'或'$'来定义你自己的空位符

　　举例：
　　PRintln(123.45678, "8.3L") -> 123.457(左对齐占八位）
　　println(123.45678, "10.3cs") -> 1.235E2 (居中占十位）
　　println(1234567, ",10") ->　 1,234,567(右对齐占十位）

// class MyOut

import java.io.PrintStream;
import java.io.PrintWriter;
import java.io.OutputStreamWriter;
import java.text.DecimalFormat;
import java.text.NumberFormat;

/* Thanks to Prof. H.Roumani.(He is my java teacher, who is great.)
*
* The format methods receive the value to be formatted (which can
* be of any type) and a format descriptor: a string that contains
* one or more of the following flags in any order and in any case:
*
* L:
*　 By default, all values are aligned right within their field
*　 width. If this flag is specified, left alignment is used instead.
*　 This flag has no effect if the field width is not specified.
* C:
*　 By default, all values are aligned right within their field
*　 width. If this flag is specified, centre alignment is used instead.
*　 This flag has no effect if the field width is not specified.
* X:
*　 By default, all numeric values are shown in the decimal system.
*　 If this flag is specified, hexadecimal is used instead (showing
*　 IEEE-754 for real's). This flag has no effect if the value is not
*　 numeric.
* B:
*　 By default, all numeric values are shown in the decimal system.
*　 If this flag is specified, binary is used instead (showing
*　 IEEE-754 for real's). This flag has no effect if the value is not
*　 numeric.
* ,:
*　 By default, all numeric, base-10 values are shown without a
*　 thousand-separator. If this flag is specified, a comma is inserted
*　 in the integer part of the number to separate thousands. This flag
*　 has no effect if the value is not numeric, is not in decimal, or if
*　 the scientific notation is used.
* S:
*　 By default, all numeric, base-10 values are shown as an integer part
*　 followed by a mantissa, or fractional part. If this flag is specified,
*　 scientific notation is used: One digits (possibly preceded by a minus
*　 sign) followed by a decimal point, a mantissa, the letter 'E' and an
*　 eXPonent. This flag has no effect if the value is not numeric or is not
*　 in decimal.
* Z:
*　 By default, all integer, base-10 values are shown with leading or
*　 trailing spaces to fill the specified field width. If this flag is
*　 specified, the field is filled with leading zeros instead. This flag is
*　 only meaningful if the value is a base-10 integer, the width is specified,
*　 and the thousand-separator flag is not specified.
* w.d (two integers separated by a period):
*　 w is the desired width of the entire returned string, after formatting.
*　 If the formatted string is shorter than w, it will be padded by leading
*　 and/or trailing spaces (or some other fill character) depending on the
*　 requested alignment (left, right, or centre). d is the desired number of
*　 decimals and is meaningful only if the value is a base-10 real (in standard
*　 or scientific notation). Rounding to the specified number of decimals is
*　 done using conventional rules but the case of 5 is handled by rounding to
*　 the nearest even number (same as the rint method of the Math class). Note
*　 that you can specify only w (in that case don't include the period), or
*　 only d (in this last case do precede it by the period).
*/