Completing tasks
- Java course
- Beginner
- Lesson 86/116
- 6 min
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.
Practice 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().
Starter code
import java.util.ArrayList;
public class Main {
public static void main(String[] args) {
TodoList list = new TodoList();
list.addTask("Shopping");
list.addTask("Homework");
// Mark the first task as completed
// List the tasks
}
}
class Task {
String title;
boolean done;
Task(String title) {
this.title = title;
this.done = false;
}
public String toString() {
return (done ? "[x] " : "[ ] ") + title;
}
}
class TodoList {
ArrayList<Task> tasks = new ArrayList<>();
void addTask(String title) {
tasks.add(new Task(title));
}
void listTasks() {
for (Task t : tasks) {
System.out.println(t);
}
}
// Define completeTask(int index): mark the task at that index as done
}Sample solution
// inside TodoList:
void completeTask(int index) {
tasks.get(index).done = true;
}
// inside main:
list.completeTask(0);
list.listTasks();Expected output
[x] Shopping [ ] Homework
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does tasks.get(0) return?
- The first Task object
- The title of the first task
- boolean done Correct answer
- The index 0
Explanation: get(0) returns the first Task object itself.
2 Match call to meaning
| Term | 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 |
3 Fill in the blank: complete the task
void completeTask(int index) {
tasks.____(index).done = true;
}void completeTask(int index) {
tasks.get(index).done = true;
}Explanation: tasks.get(index).done = true completes the task.