<b>JDK5新特点之新的格局化输出</b>[Java编程]

System.out.printf("Pi is approximately %f", Math.Pi);

printf()和 format() 办法具有相同的功效. System.out 是 java.io.PrintStream的实例. PrintStream, java.io.PrintWriter, 和 java.lang.String 每个类都有四个新的格局化办法:

format( String format, Object... args);

printf( String format, Object... args);

format( Locale locale, String format, Object... args);

printf( Locale locale, String format, Object... args);

同时,从前的formatter类也供应了更完善的办法来格局化,比方:

formatter.format("Pi is approximately %1$f," +

"and e is about %2$f", Math.PI, Math.E);

格局化元素的构成以下:

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

此中:

argument_index是一个正整数,阐明了参数的位置,1为取第一个参数

width表示输出的最小字母个数

precision代表数字的小数位数

conversion代表被格局化的参数的范例:

f float,

t time

d decimal

o octal

x hexadecimal

s general

c a Unicode character

以下是个例子:

package format;

import java.util.Formatter;

public class UsingFormatter {

public static void main(String[] args) {

if (args.length != 1) {

System.err.println("usage: " +

"java format/UsingFormatter ");

System.exit(0);

}

String format = args[0];

StringBuilder stringBuilder = new StringBuilder();

Formatter formatter = new Formatter(stringBuilder);

formatter.format("Pi is approximately " + format +

", and e is about " + format, Math.PI, Math.E);

System.out.println(stringBuilder);

}

}

//掌握台调用

java format/UsingFormatter %f

//输出

Pi is approximately 3.141593, and e is about 2.718282

//掌握台调用

java format/UsingFormatter %.2f

//输出

Pi is approximately 3.14, and e is about 2.72

//掌握台调用

java format/UsingFormatter %6.2f

//输出(有空格来弥补长度)

Pi is approximately 3.14, and e is about 2.72

//掌握台调用

java format/UsingFormatter %1$.2f

//输出

Pi is approximately 3.14, and e is about 3.14

//改变区域设置

package format;

import java.util.Formatter;

import java.util.Locale;

public class UsingFormatter {

public static void main(String[] args) {

if (args.length != 1) {

System.err.println("usage: " +

"java format/UsingFormatter <format string>");

System.exit(0);

}

String format = args[0];

StringBuilder stringBuilder = new StringBuilder();

Formatter formatter = new Formatter(stringBuilder,

Locale.FRANCE);

formatter.format("Pi is approximately " + format +

", and e is about " + format, Math.PI, Math.E);

System.out.println(stringBuilder);

}

}

//掌握台调用

java format/UsingFormatter %.2f

//输出

Pi is approximately 3,14, and e is about 2,72

//采取format,printf的可替换写法

package format;

public class UsingSystemOut {

public static void main(String[] args) {

if (args.length != 1) {

System.err.println("usage: " +

"java format/UsingSystemOut <format string>");

System.exit(0);

}

String format = args[0];

System.out.format("Pi is approximately " + format +

", and e is approximately " + format, Math.PI, Math.E);

}

}

//掌握台调用

java format/UsingSystemOut %.2f%n

//输出

Pi is approximately 3.14

, and e is about 2.72

对时间的格局化用字母t来代表,普通在t背面加上特别的字符来显示时间的某个部份:

tr hour and minute,

tA the day of the week

tB the name of the month

te the number of the day of the month

tY the year

//eg.

package format;

import java.util.Calendar;

public class FormattingDates {

public static void main(String[] args) {

System.out.printf("Right now it is %tr on " +

"%<tA, %<tB %<te, %<tY.%n",

Calendar.getInstance());

}

}

//阐明:“<”指导采取的参数为前一个被格局化的参数

//输出

Right now it is 01:55:19 PM on Wednesday, September 22, 2004.