JDK5新特性之二----新的格式化输出
2007-02-18 23:29
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JDK5.0允许象C语言那样直接用printf()方法来格式化输出,并且提供了许多参数来格式化输入,调用也很简单:
同时,以前的formatter类也提供了更完善的方法来格式化,例如:
格式化元素的构成如下:
以下是个例子:
对时间的格式化用字母t来代表,通常在t后面加上特殊的字符来显示时间的某个部分:
System.out.format("Pi is approximately %f", Math.Pi); System.out.printf("Pi is approximately %f", Math.Pi); printf()和 format()方法具有相同的功能. 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式化方法: format( String format, Object... args); printf( String format, Object... args); format( Locale locale, String format, Object... args); printf( Locale locale, String format, Object... args); |
formatter.format("Pi is approximately %1$f," + "and e is about %2$f", Math.PI, Math.E); |
%[argument_index$][flags][width][.precision]conversion 其中: argument_index是一个正整数,说明了参数的位置,1为取第一个参数 width表示输出的最小字母个数 precision代表数字的小数位数 conversion代表被格式化的参数的类型: ffloat, ttime ddecimal ooctal xhexadecimal sgeneral ca Unicode character |
package format; import java.util.Formatter; public class UsingFormatter { public static void main(String[] args) { if (args.length != 1) { System.err.println("usage: " + "java format/UsingFormatter "); System.exit(0); } String format = args[0]; StringBuilder stringBuilder = new StringBuilder(); Formatter formatter = new Formatter(stringBuilder); formatter.format("Pi is approximately " + format + ", and e is about " + format, Math.PI, Math.E); System.out.println(stringBuilder); } } //控制台调用 java format/UsingFormatter %f //输出 Pi is approximately 3.141593, and e is about 2.718282 //控制台调用 java format/UsingFormatter %.2f //输出 Pi is approximately 3.14, and e is about 2.72 //控制台调用 java format/UsingFormatter %6.2f //输出(有空格来填补长度) Pi is approximately 3.14, and e is about 2.72 //控制台调用 java format/UsingFormatter %1$.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); } } //控制台调用 java format/UsingFormatter %.2f //输出 Pi is approximately 3,14, and e is about 2,72 //采用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); } } //控制台调用 java format/UsingSystemOut %.2f%n //输出 Pi is approximately 3.14 , and e is about 2.72 |
tr hour and minute,tAthe day of the week tBthe name of the month tethe number of the day of the month tYthe 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:“<”指示采用的参数为前一个被格式化的参数 //输出 Right now it is 01:55:19 PM on Wednesday, September 22, 2004. |
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