JDK5新特性之新的名目化输出
JDK5.0答允象C语言那样直接用printf()要领来名目化输出，而且提供了很多参数来名目化输入，挪用也很简朴：
System.out.format("Pi is approximately %f", Math.Pi);
System.out.printf("Pi is approximately %f", Math.Pi);
printf()和 format() 要领具有沟通的成果. 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名目化要领:
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，以前的formatter类也提供了更完善的要领来名目化，譬喻：
formatter.format("Pi is approximately %1$f," +
"and e is about %2$f", Math.PI, Math.E);
名目化元素的组成如下：
%[argument_index$][flags][width][.precision]conversion
个中：
argument_index是一个正整数，说明白参数的位置，1为取第一个参数
width暗示输出的最小字母个数
precision代表数字的小数位数
conversion代表被名目化的参数的范例：
f float,
t time
d decimal
o octal
x hexadecimal
s general
c a Unicode character
以下是个例子：
package format;
import java.util.Formatter;
public class UsingFormatter {
public static void main(String[] args) {
if (args.length != 1) {
System.err.println("usage: " +
"java format/UsingFormatter ");
System.exit(0);
}
String format = args[0];
StringBuilder stringBuilder = new StringBuilder();
Formatter formatter = new Formatter(stringBuilder);
formatter.format("Pi is approximately " + format +
", and e is about " + format, Math.PI, Math.E);
System.out.println(stringBuilder);
}
}
//节制台挪用
java format/UsingFormatter %f
//输出
Pi is approximately 3.141593, and e is about 2.718282
//节制台挪用
java format/UsingFormatter %.2f
//输出
Pi is approximately 3.14, and e is about 2.72
//节制台挪用
java format/UsingFormatter %6.2f
//输出(有空格来填补长度)
Pi is approximately 3.14, and e is about 2.72
//节制台挪用
java format/UsingFormatter %1$.2f
//输出
Pi is approximately 3.14, and e is about 3.14
//改变区域配置
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);
}
}
//节制台挪用
java format/UsingFormatter %.2f
//输出
Pi is approximately 3,14, and e is about 2,72
//回收format,printf的可替代写法
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);
}
}
//节制台挪用
java format/UsingSystemOut %.2f%n
//输出
Pi is approximately 3.14
, and e is about 2.72
对时间的名目化用字母t来代表，凡是在t后头加上非凡的字符来显示时间的某个部门：
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());
}
}
//说明：“<”指示回收的参数为前一个被名目化的参数
//输出
Right now it is 01:55:19 PM on Wednesday, September 22, 2004.
