Listing tasks
- Java course
- Beginner
- Lesson 85/116
- 6 min
Print tasks with listTasks.
Listing tasks: listTasks
Now we will add a method to TodoList that prints tasks in a readable form: listTasks. This method prints each task on its own line.
void listTasks() {
for (Task t : tasks) {
System.out.println(t);
}
}The for-each loop puts each Task from the list into the t variable in turn. println(t) then calls the toString method and prints a readable line like [ ] Shopping.
Empty list case
When the list is empty, listTasks prints nothing; the for-each loop runs zero times. This silent behavior is usually what we want.
TodoList empty = new TodoList();
empty.listTasks();
// (the call ends without printing anything)If you wish, you can print a notice at the top with if (tasks.isEmpty()). For now we keep it simple; you can customize this later.
Practice Write the listTasks method
Inside the TodoList class, define void listTasks(); the body should walk with for (Task t : tasks) and print each task with System.out.println(t). In main, add two tasks and call 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");
// 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));
}
// Define the listTasks method: print each task on its own line
}Sample solution
// inside TodoList:
void listTasks() {
for (Task t : tasks) {
System.out.println(t);
}
}
// inside main:
list.listTasks();Expected output
[ ] Shopping [ ] Homework
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match part to purpose
| Term | Meaning |
|---|---|
for (Task t : tasks) |
Walks the list |
println(t) |
Prints the task |
toString |
Turns the task into text |
tasks |
The list of all tasks |
2 What does listTasks do when the list is empty?
- It prints nothing
- It prints null Correct answer
- It throws an error
- It prints an empty line
Explanation: For-each runs zero times on an empty list.
3 Fill in the blank: listTasks loop
void listTasks() {
for (Task t : ____) {
System.out.println(t);
}
}void listTasks() {
for (Task t : tasks) {
System.out.println(t);
}
}Explanation: for (Task t : tasks) walks the list.