Java programs to add left padding to a string in such a way that total string length should be a fixed predefined number. For example, if we have a string of length 10
, and we want to increase it’s length to 15
– by adding left padding then use the example given this post.
1. How left padding is added
When you add left padding, you essentially add a character repeatedly until string length reaches to defined length.
For example –
howtodoinjava.com //no padding howtodoinjava.com //left padding of 4 spaces ....howtodoinjava.com //left padding of 4 dots 0000howtodoinjava.com //left padding of 4 zeros
Read More: Java remove leading whitespaces from String
2. Java left padding with spaces
To add left padding, most useful and easy way is to use StringUtils.leftPad() method.
2.1. Maven dependency
<dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-lang3</artifactId> <version>3.8</version> </dependency>
2.2. Method Syntax (overloaded)
/** * @param str - the String to pad out, may be null * @param size - the size to pad to i.e. Total length of result string * @param padChar - the character or string to pad with * * @return left padded String or original String if no padding is necessary or if null String input */ public static String leftPad(final String str, final int size) {...} public static String leftPad(final String str, final int size, String padStr) {...} public static String leftPad(final String str, final int size, final char padChar) { ... }
2.3. Left padding example
System.out.println( StringUtils.leftPad("howtodoinjava", 20, " ") ); System.out.println( StringUtils.leftPad("howtodoinjava", 30, " ") ); System.out.println( StringUtils.leftPad("howtodoinjava", 15, " ") );
Program output:
howtodoinjava howtodoinjava howtodoinjava
3. Java left pad a string with zeros
Java program to use StringUtils.leftPad()
method to left pad a string with zeros, by adding leading zeros to string.
System.out.println( StringUtils.leftPad("0123456789", 10, "0") ); System.out.println( StringUtils.leftPad("789", 10, "0") ); System.out.println( StringUtils.leftPad("56789", 10, "0") );
Program output:
0123456789 0000000789 0000056789
4. Summary
In above examples, we learned to left pad string with spaces to fixed length. We also saw to left pad a number with zeros.
Use this left padding to format strings to fixed length – to display in UI.
Happy Learning !!
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