How to Check if the String Contains only Digits

In this post, we will write a Java program to checks if the String contains only Unicode digits.

Program explanation

This program uses Character.isDigit(cs.charAt(i) method to check if the character is digit or not.testIsNumeric() - JUnit test case for testing this program.

How to Check if the String Contains only Digits

Let's write a Java method to check if the given String contains only digits:

private static boolean isNumeric(final CharSequence cs) {
        if (isEmpty(cs)) {
            return false;
        }
        final int sz = cs.length();
        for (int i = 0; i < sz; i++) {
            if (!Character.isDigit(cs.charAt(i))) {
                return false;
            }
        }
        return true;
    }

Let's write a complete Java program with JUnit test cases to test the above method:

import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;

import org.junit.Test;

/**
 * How to Checks Checks if the String contains only digits
 * @author javaguides.net
 *
 */
public class IsNumiricExample {

    private static boolean isEmpty(final CharSequence cs) {
        return cs == null || cs.length() == 0;
    }

    private static boolean isNumeric(final CharSequence cs) {
        if (isEmpty(cs)) {
            return false;
        }
        final int sz = cs.length();
        for (int i = 0; i < sz; i++) {
            if (!Character.isDigit(cs.charAt(i))) {
                return false;
            }
        }
        return true;
    }

    @Test
    public void testIsNumeric() {
        assertFalse(isNumeric(null));
        assertFalse(isNumeric(""));
        assertFalse(isNumeric(" "));
        assertFalse(isNumeric("a"));
        assertFalse(isNumeric("A"));
        assertFalse(isNumeric("kgKgKgKgkgkGkjkjlJlOKLgHdGdHgl"));
        assertFalse(isNumeric("ham kso"));
        assertTrue(isNumeric("1"));
        assertTrue(isNumeric("1000"));
        assertTrue(isNumeric("\u0967\u0968\u0969"));
        assertFalse(isNumeric("\u0967\u0968 \u0969"));
        assertFalse(isNumeric("2.3"));
        assertFalse(isNumeric("10 00"));
        assertFalse(isNumeric("hkHKHik6iUGHKJgU7tUJgKJGI87GIkug"));
        assertFalse(isNumeric("_"));
        assertFalse(isNumeric("hkHKHik*khbkuh"));
        assertFalse(isNumeric("+123"));
        assertFalse(isNumeric("-123"));
    }
}

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

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