<b>JDK5新特点之新的格局化输出</b>[Java编程]
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JDK5.0答应象C语言那样直接用printf()办法来格局化输出,并且供应了很多参数来格局化输入,调用也很简单:
System.out.format("Pi is approximately %f", Math.Pi);
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.
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