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Java - check if string only contains letters
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In this article, we would like to show you how to check if the string only contains letters in Java.
In this example, we use a regular expression (regex) with Pattern.matcher() to check if the strings contain only letters.
xxxxxxxxxx1
import java.util.regex.Matcher;2
import java.util.regex.Pattern;3
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public class Example {5
6
public static void main(String[] args) {7
String letters = "ABCD";8
String numbers = "1234";9
String mixed = "a12b";10
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String regex = "^[a-zA-Z]+$"; // regex to check if string contains only letters12
Pattern pattern = Pattern.compile(regex); // compiles the regex13
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// find match between given string and pattern15
Matcher matcherLetters = pattern.matcher(letters);16
Matcher matcherNumbers = pattern.matcher(numbers);17
Matcher matcherMixed = pattern.matcher(mixed);18
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// return true if the string matched the regex20
Boolean lettersMatches = matcherLetters.matches();21
Boolean numbersMatches = matcherNumbers.matches();22
Boolean mixedMatches = matcherMixed.matches();23
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System.out.println(lettersMatches); // true25
System.out.println(numbersMatches); // false26
System.out.println(mixedMatches); // false27
}28
}Output:
xxxxxxxxxx1
true2
false3
falseIn this example, we create a function that loops through the string and checks if each character is a letter with Character.isLetter(char ch) method.
Practical example:
xxxxxxxxxx1
public class Example {2
3
public static void main(String[] args) {4
String letters = "ABC";5
String numbers = "1234";6
String mixed = "1ab2";7
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System.out.println(onlyLetters(letters)); // true9
System.out.println(onlyLetters(numbers)); // false10
System.out.println(onlyLetters(mixed)); // false11
}12
13
public static boolean onlyLetters(String string) {14
if (string == null || string.isEmpty()) {15
return false;16
}17
for (int i = 0; i < string.length(); ++i) {18
if (!Character.isLetter(string.charAt(i))) {19
return false;20
}21
}22
return true;23
}24
}Output:
xxxxxxxxxx1
true2
false3
false