System.out.format的使用
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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 $###,###.### $12,345.67
Converters and Flags Used in TestFormat.java（只是例子中用到的，还有没有用到的）
Converter
| Flag | Explanation | |
|---|---|---|
| d | A decimal integer. | |
| f | A float. | |
| n |
A new line character appropriate to the platform running the application. You should always use %n, rather than \n. |
|
| tB | A date & time conversion—locale-specific full name of month. | |
| td, te | A date & time conversion—2-digit day of month. td has leading zeroes as needed, te does not. | |
| ty, tY | A date & time conversion—ty = 2-digit year, tY = 4-digit year. | |
| tl | A date & time conversion—hour in 12-hour clock. | |
| tM | A date & time conversion—minutes in 2 digits, with leading zeroes as necessary. | |
| tp | A date & time conversion—locale-specific am/pm (lower case). | |
| tm | A date & time conversion—months in 2 digits, with leading zeroes as necessary. | |
| tD | A date & time conversion—date as %tm%td%ty | |
| 08 | Eight characters in width, with leading zeroes as necessary. | |
| + | Includes sign, whether positive or negative. | |
| , | Includes locale-specific grouping characters. | |
| - | Left-justified.. | |
| .3 | Three places after decimal point. | |
| 10.3 | Ten characters in width, right justified, with three places after decimal point. |
JDK5.0允许象C语言那样直接用printf()方法来格式化输出，并且提供了许多参数来格式化输入，调用也很简单：
|
System.out.format("Pi is approximately %f", Math.Pi); System.out.printf("Pi is approximately %f", Math.Pi);
format( String format, Object... args); printf( String format, Object... args); format( Locale locale, String format, Object... args); printf( Locale locale, String format, Object... args);
|
同时，以前的formatter类也提供了更完善的方法来格式化，例如：
|
formatter.format("Pi is approximately %1$f," + "and e is about %2$f", Math.PI, Math.E);
|
格式化元素的构成如下：
|
%[argument_index$][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：
|
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); } }
//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
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
|
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：
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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