Change project structure to a Maven Java project + Refactor (#2816)

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

@@ -0,0 +1,30 @@
+package com.thealgorithms.strings;
+
+public class Upper {
+
+    /**
+     * Driver Code
+     */
+    public static void main(String[] args) {
+        String[] strings = {"ABC", "ABC123", "abcABC", "abc123ABC"};
+        for (String s : strings) {
+            assert toUpperCase(s).equals(s.toUpperCase());
+        }
+    }
+
+    /**
+     * Converts all of the characters in this {@code String} to upper case
+     *
+     * @param s the string to convert
+     * @return the {@code String}, converted to uppercase.
+     */
+    public static String toUpperCase(String s) {
+        char[] values = s.toCharArray();
+        for (int i = 0; i < values.length; ++i) {
+            if (Character.isLetter(values[i]) && Character.isLowerCase(values[i])) {
+                values[i] = Character.toUpperCase(values[i]);
+            }
+        }
+        return new String(values);
+    }
+}