如何在 Java 中向数字添加左填充零？
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How do I add left-padded zeros to a number in Java?
提问by Stig Christian
I have an integer 100, how do I format it to look like 00000100(always 8 digits long)?
我有一个整数100，如何将它格式化为看起来像00000100（总是 8 位数字）？
采纳答案by Andrew Hare
Try this:
尝试这个：
String formattedNumber = String.format("%08d", number);
回答by Jo?o Silva
You can also use the class DecimalFormat, like so:
您还可以使用 class DecimalFormat，如下所示：
NumberFormat formatter = new DecimalFormat("00000000");
System.out.println(formatter.format(100)); // 00000100
回答by Martijn Courteaux
This also works:
这也有效：
int i = 53;
String spaceHolder = "00000000";
String intString = String.valueOf(i);
String string = spaceHolder.substring(intString.lenght()).contract(intString);
But the other examples are much easier.
但其他示例要容易得多。
回答by Peter Lawrey
Yet another way. ;)
还是另一种方式。;)
int x = ...
String text = (""+(500000000 + x)).substring(1);
-1 => 99999999 (nines complement)
-1 => 99999999（9 的补码）
import java.util.concurrent.Callable;
/* Prints.
String.format("%08d"): Time per call 3822
(""+(500000000+x)).substring(1): Time per call 593
Space holder: Time per call 730
*/
public class StringTimer {
public static void time(String description, Callable<String> test) {
try {
// warmup
for(int i=0;i<10*1000;i++)
test.call();
long start = System.nanoTime();
for(int i=0;i<100*1000;i++)
test.call();
long time = System.nanoTime() - start;
System.out.printf("%s: Time per call %d%n", description, time/100/1000);
} catch (Exception e) {
System.out.println(description+" failed");
e.printStackTrace();
}
}
public static void main(String... args) {
time("String.format(\"%08d\")", new Callable<String>() {
int i =0;
public String call() throws Exception {
return String.format("%08d", i++);
}
});
time("(\"\"+(500000000+x)).substring(1)", new Callable<String>() {
int i =0;
public String call() throws Exception {
return (""+(500000000+(i++))).substring(1);
}
});
time("Space holder", new Callable<String>() {
int i =0;
public String call() throws Exception {
String spaceHolder = "00000000";
String intString = String.valueOf(i++);
return spaceHolder.substring(intString.length()).concat(intString);
}
});
}
}
回答by Adam Gent
If you need to parse this string and or support i18n consider extending the
如果您需要解析此字符串和/或支持 i18n，请考虑扩展
java.text.Format
object. Use the other answers to help you get the format.
目的。使用其他答案来帮助您获得格式。
回答by Denis Tulskiy
If you just need to print it out, this is a shorter version:
如果您只需要打印出来，这是一个较短的版本：
System.out.printf("%08d\n", number);
回答by Dag
If Google Guava is an Option:
如果谷歌番石榴是一个选项：
String output = Strings.padStart("" + 100, 8, '0');
Alternatively Apache Commons Lang:
或者 Apache Commons Lang：
String output = StringUtils.leftPad("" + 100, 8, "0");
