程序中常常遇見：控制數據格式化輸出。而控制選項繁多，有時會忘記。該文做一個小結，作為以后參考引用。

整型數據(short, int等)

%d??? A regular base-10 integer, such as 987

%o??? A base-8 octal integer, such as 1733

%x??? A base-16 lowercase hexadecimal integer, such as 3db

%X??? A base-16 uppercase hexademical integer, such as 3DB

浮點型數據(float, double)

%f??? A regular base-10 decimal number, such as 3.141593

%e??? A decimal number in scientific notation with a lowercase e, such as 3.141593e+00

%E??? A decimal number in scientific notation with an uppercase E, such as 3.141593E+00

%g??? A decimal number formatted in either regular or scientific notation, depending on its size and precision, with a lowercase e if scientific notation is used

%G??? A decimal number formatted in either regular or scientific notation, depending on its size and precision, with an uppercase E if scientific notation is used

%a??? A lowercase hexadecimal floating-point number, such as 0x1.921fb54442d18p1

%A??? An uppercase hexadecimal floating-point number, such as 0x1.921FB5442D18P1

對于浮點型數據，有時還需要控制輸出的寬度，精度或者其它。這時需要用到格式修飾符(Format Modifiers)。格式修飾符遵照一定的模式:

%[argument_index$][flags][width][.precision]conversion

argument_index:??? The number of the argument with which to replace this tag

flags:??? Indicators of various formatting options

width:??? The minimum number of characters with which to format the replacement value

precision:??? The number of characters after the decimal point; alternatively, the maximum number of characters in the formatted string

Flag	Signifies	Applies to
-	Left-justify	All
#	Alternate form	General, integer, floating
+	Include a sign even if positive (Normally, only negative numbers have signs)	Integer, floating point
space	Add a leading space to positive numbers (This is where the sign would be and helps line up positive and negative numbers)	Integer, floating point
0	Pad with zeros instead of spaces	Integer, floating point
,	Use the locale-specific grouping separator instead of a period	Integer, floating point
#	Use instead of a minus sign to indicate negative numbers	Integer, floating point

盡管選項繁多，使用最多的還是控制輸出的寬度和精度。

Example 1: 控制寬度和精度

System.out.printf(“%5.3f”, Math.PI)，控制輸出寬度為5，精度為3，結果為

“ 3.142”(輸出的最前面有一個空格)

Example 2: 使用argument_index

System.out.printf(“%s and %s”, “You”, “Me”)輸出”You and Me”

System.out.printf(“%2$s and %2$s”, “You”, “Me”)輸出”Me and Me”

轉載于:https://www.cnblogs.com/RayLee/archive/2011/02/24/1963687.html

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