public class TextEditor {
   private SpellChecker spellChecker;

   public TextEditor(SpellChecker spellChecker) {
      this.spellChecker = spellChecker;
   }
}

Spellchecker 被注入到 TextEditor 的建構元裡面

The code is cleaner with the DI principle and decoupling is more effective when objects are provided with their dependencies.