Todo list class

Todo.java

public class Todo {
  private final Map<String, Set<TodoItem>> tasks;
  private final Map<String, TodoItem> allTasks;
  
  public Todo() {
    tasks = new HashMap<>();
    allTasks = new HashMap<>();
  }
  
  public Todo(File f) {
    this();
    load(f);
  }
  
  public void load(File f) {
    Scanner scanner = null;
    try {
      scanner = new Scanner(f);
      Set<TodoItem> cat = null;
      while (scanner.hasNext()) {
        String line = scanner.nextLine();
        if (line.beginsWith(':')) {
          cat = getCategory(line.substring(1));
        } else {
          cat.add(new TodoItem(line));
        }
      }
    } catch (IOException e) {
      if (scanner != null) {
        try {
          scanner.close();
        } catch (IOException ignored) {}
      }
      throw new RuntimeException("Exception loading state!", e);
    }
  }
  
  public void save(File f) {
    Writer writer = null;
    try {
      writer = new FileWriter(f);
      for (String catName : tasks.keySet()) {
        writer.write(":" + catName + "\n");
        Set<TodoItem> cat = tasks.get(catName);
        for (TodoItem task : cat) {
          writer.write(task.item.trim() + "\n");
        }
      }
      writer.close();
    } catch (IOException e) {
      if (writer != null) {
        try {
          writer.close();
        } catch (IOException ignored) {}
      }
      throw new RuntimeException("Exception saving list!", e);
    }
  }
  
  private Set<TodoItem> getCategory(String name) {
    Set<TodoItem> cat = tasks.get(name);
    if (cat == null) {
      tasks.put(name, cat = new HashSet<>());
    }
    return cat;
  }
  
  public void addItem(String task, File f, String ... categories) {
    addItem(task, categories);
    save(f);
  }
    
  public void addItem(String task, String ... categories) {
    TodoItem todo = new TodoItem(task);
    allTasks.put(task, todo);
    for (String cat : categories) {
      getCategory(cat).add(todo);
    }
  }
  
  public void deleteItem(String task, File f, String ... categories) {
    deleteItem(task, categories);
    save(f);
  }
  
  public void deleteItem(String task, String ... categories) {
    TodoItem todo = new TodoItem(task);
    allTasks.remove(todo);
    for (String cat : categories) {
      getCategory(cat).remove(todo);
    }
  }
  
  public void updateItem(String task, String newTask) {
    TodoItem todo = allTasks.get(task);
    if (todo != null) {
      todo.item = newTask;
    }
  }
  
  public void viewList() {
    for (String catName : tasks.keySet()) {
      viewCategory(catName);
    }
  }
  
  public void viewCategory(String catName) {
    System.out.println("Tasks in category \"" + catName + "\":\n");
    Set<TodoItem> cat = tasks.get(catName);
    for (TodoItem task : cat) {
      System.out.println("  " + task.item + "\n");
    }
  }
  
  public static void main(String[] args) {
    Todo todo = new Todo();
    todo.addItem("Work on easy DP challenge", "programming");
    todo.addItem("Work on intermediate DP challenge", "programming");
    todo.save("./tasks.lst");
    
    todo = new Todo("./tasks.lst");
    todo.viewList();
  }
  
  private static class TodoItem {
    private String item;
    
    public TodoItem(item) {
      this.item = item;
    }
    
    public int hashCode() {
      return item.hashCode();
    }
    
    public boolean equals(Object other) {
      if (other == this) return true;
      if (!(other instanceof TodoItem)) return false;
      return item.equals(((TodoItem)other).item);
    }
  }
}