Testen en uitbreidingen

public class Main {
  public static void main(String[] args) {
    // Very small test set for beginners. Each case prints a short result.
    String[] samples = new String[] {
      "Hello world hello",
      "",                            // empty
      "   ",                         // spaces
      "Hello, HELLO, hello!",        // mixed case and punctuation
      "Numbers 1 2 3 and words",     // numbers and words
      "Only... punctuation!!!"       // punctuation only
    };

    for (int t = 0; t < samples.length; t = t + 1) {
      String text = samples[t];
      System.out.println("-- Case " + (t + 1) + " --");
      // 1) Lowercase
      String lower = text.toLowerCase();
      // 2) Replace non letters with spaces
      String cleaned = lower.replaceAll("[^a-z]+", " ");
      // 3) Split on spaces and filter empties
      String[] tokens = cleaned.trim().split("\\s+");

      java.util.Map<String, Integer> freq = new java.util.HashMap<>();
      int total = 0;
      for (int i = 0; i < tokens.length; i = i + 1) {
        String w = tokens[i];
        if (w.length() == 0) continue;
        // Optional tiny extension: skip one letter words like "a"
        if (w.length() == 1) continue;
        total = total + 1;
        Integer c = freq.get(w);
        if (c == null) freq.put(w, 1);
        else freq.put(w, c + 1);
      }

      // Print a very small summary (no top N here to keep it simple)
      System.out.println("Total words: " + total);
      System.out.println("Unique words: " + freq.size());
    }
  }
}