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The object that protects itself

A basket whose rules live in every caller. Move them inside.

Beginner12 min on the clock4 graded checks · 100 pointsObjects That Behave

Graded by running your code against real cases.

What you build

Make the items unreachable from outside the class
Add through a method that rejects a quantity of zero or less
Adding the same sku twice should increase the quantity, not duplicate the line
Expose the lines for reading without handing over the array itself
Expose a count derived from the items

Done means

No caller outside the class can put the basket into a state its methods would refuse.

How it is graded

Published in full, before you start — every point is one of these and there is nothing else. Each one runs your code; it is not a search for keywords.

The items cannot be reached from outside+30Objects that protect themselves
It refuses a quantity that makes no sense+25Objects that protect themselves
The same sku twice is one line+20Objects that protect themselves
The contents are readable and the count is derived+25Objects that protect themselves

What it teaches

Objects that protect themselvesbeginner

If a caller can reach the data, every rule you wrote about it is optional — and a getter that hands back the real array is the most common way that happens.

The rest of Objects That Behave

One caller, many shapesIntermediate · 15 min Has-a beats is-aIntermediate · 15 min The subclass that broke its parentAdvanced · 18 min