问题
How do you left pad an int with zeros when converting to a String in java?
I\'m basically looking to pad out integers up to 9999 with leading zeros (e.g. 1 = 0001).
回答1:
Use java.lang.String.format(String,Object...) like this:
String.format("%05d", yournumber);
for zero-padding with a length of 5. For hexadecimal output replace the d with an x as in "%05x".
The full formatting options are documented as part of java.util.Formatter.
回答2:
If you for any reason use pre 1.5 Java then may try with Apache Commons Lang method
org.apache.commons.lang.StringUtils.leftPad(String str, int size, '0')
回答3:
Let's say you want to print 11 as 011
You could use a formatter: "%03d".
You can use this formatter like this:
int a = 11;
String with3digits = String.format("%03d", a);
System.out.println(with3digits);
Alternatively, some java methods directly support these formatters:
System.out.printf("%03d", a);
回答4:
Found this example... Will test...
import java.text.DecimalFormat;
class TestingAndQualityAssuranceDepartment
{
public static void main(String [] args)
{
int x=1;
DecimalFormat df = new DecimalFormat("00");
System.out.println(df.format(x));
}
}
Tested this and:
String.format("%05d",number);
Both work, for my purposes I think String.Format is better and more succinct.
回答5:
If performance is important in your case you could do it yourself with less overhead compared to the String.format function:
/**
* @param in The integer value
* @param fill The number of digits to fill
* @return The given value left padded with the given number of digits
*/
public static String lPadZero(int in, int fill){
boolean negative = false;
int value, len = 0;
if(in >= 0){
value = in;
} else {
negative = true;
value = - in;
in = - in;
len ++;
}
if(value == 0){
len = 1;
} else{
for(; value != 0; len ++){
value /= 10;
}
}
StringBuilder sb = new StringBuilder();
if(negative){
sb.append('-');
}
for(int i = fill; i > len; i--){
sb.append('0');
}
sb.append(in);
return sb.toString();
}
Performance
public static void main(String[] args) {
Random rdm;
long start;
// Using own function
rdm = new Random(0);
start = System.nanoTime();
for(int i = 10000000; i != 0; i--){
lPadZero(rdm.nextInt(20000) - 10000, 4);
}
System.out.println("Own function: " + ((System.nanoTime() - start) / 1000000) + "ms");
// Using String.format
rdm = new Random(0);
start = System.nanoTime();
for(int i = 10000000; i != 0; i--){
String.format("%04d", rdm.nextInt(20000) - 10000);
}
System.out.println("String.format: " + ((System.nanoTime() - start) / 1000000) + "ms");
}
Result
Own function: 1697ms
String.format: 38134ms
回答6:
You can use Google Guava:
Maven:
<dependency>
<artifactId>guava</artifactId>
<groupId>com.google.guava</groupId>
<version>14.0.1</version>
</dependency>
Sample code:
String paddedString1 = Strings.padStart("7", 3, '0'); //"007"
String paddedString2 = Strings.padStart("2020", 3, '0'); //"2020"
Note:
Guava is very useful library, it also provides lots of features which related to Collections, Caches, Functional idioms, Concurrency, Strings, Primitives, Ranges, IO, Hashing, EventBus, etc
Ref: GuavaExplained
回答7:
Try this one:
import java.text.DecimalFormat;
DecimalFormat df = new DecimalFormat("0000");
String c = df.format(9); // 0009
String a = df.format(99); // 0099
String b = df.format(999); // 0999
回答8:
Although many of the above approaches are good, but sometimes we need to format integers as well as floats. We can use this, particularly when we need to pad particular number of zeroes on left as well as right of decimal numbers.
import java.text.NumberFormat;
public class NumberFormatMain {
public static void main(String[] args) {
int intNumber = 25;
float floatNumber = 25.546f;
NumberFormat format=NumberFormat.getInstance();
format.setMaximumIntegerDigits(6);
format.setMaximumFractionDigits(6);
format.setMinimumFractionDigits(6);
format.setMinimumIntegerDigits(6);
System.out.println("Formatted Integer : "+format.format(intNumber).replace(",",""));
System.out.println("Formatted Float : "+format.format(floatNumber).replace(",",""));
}
}
回答9:
int x = 1;
System.out.format("%05d",x);
if you want to print the formatted text directly onto the screen.
回答10:
Use the class DecimalFormat, like so:
NumberFormat formatter = new DecimalFormat("0000"); //i use 4 Zero but you can also another number
System.out.println("OUTPUT : "+formatter.format(811));
OUTPUT : 0000811
回答11:
Check my code that will work for integer and String.
Assume our first number is 2. And we want to add zeros to that so the the length of final string will be 4. For that you can use following code
int number=2;
int requiredLengthAfterPadding=4;
String resultString=Integer.toString(number);
int inputStringLengh=resultString.length();
int diff=requiredLengthAfterPadding-inputStringLengh;
if(inputStringLengh<requiredLengthAfterPadding)
{
resultString=new String(new char[diff]).replace("\0", "0")+number;
}
System.out.println(resultString);
回答12:
You need to use a Formatter, following code uses NumberFormat
int inputNo = 1;
NumberFormat nf = NumberFormat.getInstance();
nf.setMaximumIntegerDigits(4);
nf.setMinimumIntegerDigits(4);
nf.setGroupingUsed(false);
System.out.println("Formatted Integer : " + nf.format(inputNo));
Output: 0001
回答13:
public static String zeroPad(long number, int width) {
long wrapAt = (long)Math.pow(10, width);
return String.valueOf(number % wrapAt + wrapAt).substring(1);
}
The only problem with this approach is that it makes you put on your thinking hat to figure out how it works.
回答14:
No packages needed:
String paddedString = i < 100 ? i < 10 ? "00" + i : "0" + i : "" + i;
This will pad the string to three characters, and it is easy to add a part more for four or five. I know this is not the perfect solution in any way (especially if you want a large padded string), but I like it.
来源：https://stackoverflow.com/questions/473282/how-can-i-pad-an-integer-with-zeros-on-the-left