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How can I pad an integers with zeros on the left?

Posted by: admin November 2, 2017 Leave a comment

Questions:

How do you left pad an int with zeros in java when converting to a string?

I’m basically looking to pad out integers up to 9999 with the leading zeros (e.g. 1 = “0001”).

Answers:

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.

Questions:
Answers:

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')

Questions:
Answers:

Let’s say you want to print 11 as 011

You could use a formatter: "%03d".

enter image description here

You can use this formatter like this:

int a = 11;
String with3digits = String.format("%03d", a);
String.out.println(with3digits);

Alternatively, some java methods directly support these formatters:

System.out.printf("%03d", a);

Questions:
Answers:

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.

Questions:
Answers:

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

Questions:
Answers:

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

Questions:
Answers:

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(",",""));  
 }    
}  

Questions:
Answers:
int x = 1;
System.out.format("%05d",x);

if you want to print the formatted text directly onto the screen.

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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("
    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);
", "0")+number; } System.out.println(resultString);

Questions:
Answers:
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.

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Answers:

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.