JDK5新特性：格式化输出

   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);

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

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：

f  float,

t  time

d  decimal

o octal

x  hexadecimal

s  general

c  a Unicode character

   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

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.