refactor: CharactersSame (#5396)

Author: alxkm

src/main/java/com/thealgorithms/strings/CharactersSame.java

@@ -5,25 +5,19 @@ private CharactersSame() {
     }
 
     /**
-     * Driver Code
-     */
-    public static void main(String[] args) {
-        assert isAllCharactersSame("");
-        assert !isAllCharactersSame("aab");
-        assert isAllCharactersSame("aaa");
-        assert isAllCharactersSame("11111");
-    }
-
-    /**
-     * check if all the characters of a string are same
+     * Checks if all characters in the string are the same.
      *
      * @param s the string to check
-     * @return {@code true} if all characters of a string are same, otherwise
-     * {@code false}
+     * @return {@code true} if all characters in the string are the same or if the string is empty, otherwise {@code false}
      */
     public static boolean isAllCharactersSame(String s) {
-        for (int i = 1, length = s.length(); i < length; ++i) {
-            if (s.charAt(i) != s.charAt(0)) {
+        if (s.isEmpty()) {
+            return true; // Empty strings can be considered as having "all the same characters"
+        }
+
+        char firstChar = s.charAt(0);
+        for (int i = 1; i < s.length(); i++) {
+            if (s.charAt(i) != firstChar) {
                 return false;
             }
         }

src/test/java/com/thealgorithms/strings/CharacterSameTest.java

@@ -1,28 +1,15 @@
 package com.thealgorithms.strings;
 
-import static org.junit.jupiter.api.Assertions.assertFalse;
-import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
-import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
 
-public class CharacterSameTest {
+class CharactersSameTest {
 
-    @Test
-    public void isAllCharactersSame() {
-        String input1 = "aaa";
-        String input2 = "abc";
-        String input3 = "1  1  1  1";
-        String input4 = "111";
-        String input5 = "";
-        String input6 = "           ";
-        String input7 = ".       ";
-
-        assertTrue(CharactersSame.isAllCharactersSame(input1));
-        assertFalse(CharactersSame.isAllCharactersSame(input2));
-        assertFalse(CharactersSame.isAllCharactersSame(input3));
-        assertTrue(CharactersSame.isAllCharactersSame(input4));
-        assertTrue(CharactersSame.isAllCharactersSame(input5));
-        assertTrue(CharactersSame.isAllCharactersSame(input6));
-        assertFalse(CharactersSame.isAllCharactersSame(input7));
+    @ParameterizedTest
+    @CsvSource({"aaa, true", "abc, false", "'1  1  1  1', false", "111, true", "'', true", "'           ', true", "'.       ', false", "'a', true", "'  ', true", "'ab', false", "'11111', true", "'ababab', false", "'       ', true", "'+++', true"})
+    void testIsAllCharactersSame(String input, boolean expected) {
+        assertEquals(CharactersSame.isAllCharactersSame(input), expected);
     }
 }