How Jario works

Every task has four areas:

• Editor (top left): where you write your Java code. It is saved automatically.
• Console (bottom left): what your program prints, and in the Tests tab, which tests passed.
• Task (top right): what the program should do, an example and the list of tests.
• Tutor (bottom right): an AI that helps when you're stuck.

You can drag the dividers between the areas. Double-clicking a divider restores the default size. On a phone you switch areas with the tabs at the bottom.

Run only starts your program. It doesn't tell you whether the solution is right, you just see the output. It's your playground: try things, add a println, hunt for bugs.

Check compares your program with the task's tests. Each test has its own input and expects a certain output or return value. The Tests tab shows which ones passed and what went wrong with the others.

A good routine: try it with Run first, then Check.

Some programs read input with a Scanner, for example a name or two numbers. When you Run, this input comes from the field Input for “Run” (stdin) below the console.

Put each input on its own line, just as you would type it in a real terminal:

Ada
19

If the field is empty while your program wants to read something, it stops with an error (NoSuchElementException). For Check you don't need the field: the tests bring their own input.

If your code has an error, the editor marks the line in red. The console shows Java's message, exactly as it would appear on your own computer.

For the most common errors, What does this mean? appears below it. One click explains the message in plain words, with the line where it happens. No tutor and no waiting needed.

In the bottom right sits your tutor, an AI that knows your code and the task. Ask it anything about the task: what an error message means, why a test fails or how a loop works.

• Give me a hint shows a prepared hint for the task, more concrete step by step.
• The tutor doesn't give you a finished solution. It helps you get there yourself.
• With Free you have a few questions per day, with Pro many more. Without an account the tutor isn't available.

In the task list and at the top of every task, an icon shows how far you got:

Every chapter starts with a short lesson that explains everything you need for its tasks. In every task, Read the chapter takes you back there.

Every task has a level:

• Easy: one new topic, almost step by step.
• Medium: the topic combined with loops or conditions.
• Hard: several topics, you need your own idea. These are optional: Easy and Medium are enough for the next chapter.

There are also exam-style tasks. In What does it print? you read code without running it and type the output. You can run it only once you got it right. In Find the bug the starter code contains a mistake for you to find and fix.

You can solve the first tasks without an account. Your progress then stays in your browser. If you sign up later, it is carried over.

With a free account (Free) you practise the first chapters and ask the tutor a few times a day. Pro opens all chapters and gives you more tutor questions. Practising is never limited: no hearts, no energy.

The gear icon in the top right lets you choose the language, the appearance (light, dark or like your system) and the sound after running and checking code.