Completing tasks

Update status with completeTask.

Completing tasks: completeTask

Now we will add a completeTask(int index) method that marks a task as completed. This method sets the done field of the task at the given index to true.

void completeTask(int index) {
  tasks.get(index).done = true;
}

Here tasks.get(index) fetches the Task object at that index, then .done = true updates its state. Because the object reference stays the same, the change is permanent on the task in the list.

Invalid index hazard

If you pass an index that is not in the list to completeTask, tasks.get(index) throws an IndexOutOfBoundsException. To prevent this, you can add a bounds check at the top of the method.

void completeTask(int index) {
  if (index < 0 || index >= tasks.size()) return;
  tasks.get(index).done = true;
}

For now we do not add this check; but in a real app, always validating an index that comes from the user is good practice.

Exercise Write the completeTask method

Inside TodoList, define void completeTask(int index); the body should run tasks.get(index).done = true. In main, add two tasks, call list.completeTask(0), and print with list.listTasks().

Show example solution

// inside TodoList:
void completeTask(int index) {
  tasks.get(index).done = true;
}
// inside main:
list.completeTask(0);
list.listTasks();

Test yourself

What does tasks.get(0) return?
- The first Task object
- The title of the first task
- boolean done
- The index 0
Show answer

boolean done — get(0) returns the first Task object itself.
Match call to meaning

tasks.get(0)

First task object
tasks.get(0).done = true

Complete the first task
tasks.size()

Number of tasks
tasks.add(new Task(...))

Add a new task

Fill in the blank: complete the task

void completeTask(int index) {
  tasks.____(index).done = true;
}

Show answer

void completeTask(int index) {
  tasks.get(index).done = true;
}

Next lesson: Putting it together

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