System.out.format可以格式日期，数字。。

Java格式化输出示例

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本文介绍了Java中使用System.out.format进行数据格式化的多种方法，包括整数、浮点数和日期时间的格式化技巧，并展示了如何利用DecimalFormat类自定义数值格式。

import java.util.Calendar;
import java.util.Locale;

public class TestFormat {
    
    public static void main(String[] args) {
      long n = 461012;
      System.out.format("%d%n", n);                  //  -->  "461012"
      System.out.format("%08d%n", n);                //  -->  "00461012"
      System.out.format("%+8d%n", n);                //  -->  " +461012"
      System.out.format("%,8d%n", n);                //  -->  " 461,012"
      System.out.format("%+,8d%n%n", n);             //  -->  "+461,012"
      
      double pi = Math.PI;
      System.out.format("%f%n", pi);                 //  -->  "3.141593"
      System.out.format("%.3f%n", pi);               //  -->  "3.142"
      System.out.format("%10.3f%n", pi);             //  -->  "     3.142"
      System.out.format("%-10.3f%n", pi);            //  -->  "3.142"
      System.out.format(Locale.FRANCE,
                        "%-10.4f%n%n", pi);          //  -->  "3,1416"

      Calendar c = Calendar.getInstance();
      System.out.format("%tB %te, %tY%n", c, c, c);  //  -->  "May 29, 2006"
      System.out.format("%tl:%tM %tp%n", c, c, c);   //  -->  "2:34 am"
      System.out.format("%tD%n", c);                 //  -->  "05/29/06"
    }
}

====================

import java.text.*;

public class DecimalFormatDemo {

   static public void customFormat(String pattern, double value ) {
      DecimalFormat myFormatter = new DecimalFormat(pattern);
      String output = myFormatter.format(value);
      System.out.println(value + "  " + pattern + "  " + output);
   }

static public void main(String[] args) {

      customFormat("###,###.###", 123456.789);
      customFormat("###.##", 123456.789);
      customFormat("000000.000", 123.78);
      customFormat("$###,###.###", 12345.67);
   }
}

The output is:

123456.789 ###,###.### 123,456.789
123456.789 ###.## 123456.79
123.78 000000.000 000123.780
12345.67 $###,###.### $12,345.67

**Converters and Flags Used in `TestFormat.java（只是例子中用到的，还有没有用到的）`**
Converter	Flag	Explanation
d		A decimal integer.
f		A float.
n		A new line character appropriate to the platform running the application. You should always use `%n`, rather than `\n`.
tB		A date & time conversion—locale-specific full name of month.
td, te		A date & time conversion—2-digit day of month. td has leading zeroes as needed, te does not.
ty, tY		A date & time conversion—ty = 2-digit year, tY = 4-digit year.
tl		A date & time conversion—hour in 12-hour clock.
tM		A date & time conversion—minutes in 2 digits, with leading zeroes as necessary.
tp		A date & time conversion—locale-specific am/pm (lower case).
tm		A date & time conversion—months in 2 digits, with leading zeroes as necessary.
tD		A date & time conversion—date as %tm%td%ty
	08	Eight characters in width, with leading zeroes as necessary.
	+	Includes sign, whether positive or negative.
	,	Includes locale-specific grouping characters.
	-	Left-justified..
	.3	Three places after decimal point.
	10.3	Ten characters in width, right justified, with three places after decimal point.