Resolve build errors & cleanup structure (#2334)

Strings/CharactersSame.java

@@ -0,0 +1,27 @@
+package Strings;
+
+public class 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
+   *
+   * @param s the string to check
+   * @return {@code true} if all characters of a string are same, 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)) {
+        return false;
+      }
+    }
+    return true;
+  }
+}