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Java - check if string only contains numbers
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In this article, we would like to show you how to check if the string only contains numbers in Java.
In this example, we use a regular expression (regex) with Pattern.matcher() to check if the strings contain only numbers.
xxxxxxxxxx1
import java.util.regex.Matcher;2
import java.util.regex.Pattern;3
4
public class Example {5
6
public static void main(String[] args) {7
String numbers = "1234";8
String text = "ABC";9
10
String regex = "^[0-9]+$"; // regex to check if string contains only digits11
Pattern pattern = Pattern.compile(regex); // compiles the regex12
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// find match between given string and pattern14
Matcher matcherNumbers = pattern.matcher(numbers);15
Matcher matcherText = pattern.matcher(text);16
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// return true if the string matched the regex18
Boolean numbersMatches = matcherNumbers.matches();19
Boolean textMatches = matcherText.matches();20
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System.out.println(numbersMatches); // true22
System.out.println(textMatches); // false23
}24
}Output:
xxxxxxxxxx1
true2
falseIn this example, we create a function that loops through the string and checks if each character is a digit with Character.isDigit(char ch) method.
Practical example:
xxxxxxxxxx1
public class Example {2
3
public static void main(String[] args) {4
String numbers = "1234";5
String text = "ABC";6
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System.out.println(onlyNumbers(numbers)); // true8
System.out.println(onlyNumbers(text)); // false9
}10
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public static boolean onlyNumbers(String string) {12
if (string == null || string.isEmpty()) {13
return false;14
}15
for (int i = 0; i < string.length(); ++i) {16
if (!Character.isDigit(string.charAt(i))) {17
return false;18
}19
}20
return true;21
}22
}Output:
xxxxxxxxxx1
true2
false