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

This program uses the Character.isLetter() method to check if the character is a letter or not.

How to Check if the String Contains Only Letters

Let's write a Java method to check if the given String contains only letters or not:

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

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

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;

/**
 * Checks if the CharSequence contains only Unicode letters
 * @author javaguides.net
 *
 */
public class IsAlphaExample {

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

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

    @Test
    public void testIsAlpha() {
        assertFalse(isAlpha(null));
        assertFalse(isAlpha(""));
        assertFalse(isAlpha(" "));
        assertTrue(isAlpha("a"));
        assertTrue(isAlpha("A"));
        assertTrue(isAlpha("kgKgKgKgkgkGkjkjlJlOKLgHdGdHgl"));
        assertFalse(isAlpha("ham kso"));
        assertFalse(isAlpha("1"));
        assertFalse(isAlpha("hkHKHik6iUGHKJgU7tUJgKJGI87GIkug"));
        assertFalse(isAlpha("_"));
        assertFalse(isAlpha("hkHKHik*khbkuh"));
    }
}

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