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的實例. PrintStream, java.io.PrintWriter, 和 java.lang.String 每個類都有四個新的格式化方法:
format( String format, Object... args);
printf( String format, Object... args);
format( Locale locale, String format, Object... args);
printf( Locale locale, String format, Object... args);
同時，以前的formatter類也提供了更完善的方法來格式化，例如：
formatter.format("Pi is approximately %1$f," +
"and e is about %2$f", Math.PI, Math.E);
格式化元素的構成如下：
%[argument_index$][flags][width][.precision]conversion
其中：
argument_index是一個正整數，說明了參數的位置，1為取第一個參數
width表示輸出的最小字母個數
precision代表數字的小數位數
conversion代表被格式化的參數的類型：
f float,
t time
d decimal
o octal
x hexadecimal
s general
c a Unicode character
以下是個例子：
package format;
import java.util.Formatter;
public class UsingFormatter {
public static void main(String[] args) {
if (args.length != 1) {
System.err.println("usage: " +
"java format/UsingFormatter ");
System.exit(0);
}
String format = args[0];
StringBuilder stringBuilder = new StringBuilder();
Formatter formatter = new Formatter(stringBuilder);
formatter.format("Pi is approximately " + format +
", and e is about " + format, Math.PI, Math.E);
System.out.println(stringBuilder);
}
}
//控制台調用
java format/UsingFormatter %f
//輸出
Pi is approximately 3.141593, and e is about 2.718282
//控制台調用
java format/UsingFormatter %.2f
//輸出
Pi is approximately 3.14, and e is about 2.72
//控制台調用
java format/UsingFormatter %6.2f
//輸出(有空格來填補長度)
Pi is approximately 3.14, and e is about 2.72
//控制台調用
java format/UsingFormatter %1$.2f
//輸出
Pi is approximately 3.14, and e is about 3.14
//改變區域設置
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);
}
}
//控制台調用
java format/UsingFormatter %.2f
//輸出
Pi is approximately 3,14, and e is about 2,72
//采用format,printf的可替代寫法
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);
}
}
//控制台調用
java format/UsingSystemOut %.2f%n
//輸出
Pi is approximately 3.14
, and e is about 2.72
對時間的格式化用字母t來代表，通常在t後面加上特殊的字符來顯示時間的某個部分：
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());
}
}
//說明：“<”指示采用的參數為前一個被格式化的參數
//輸出
Right now it is 01:55:19 PM on Wednesday, September 22, 2004.
