Big idea: You don't have to write everything yourself. Libraries provide ready-made classes, and the API documentation tells you how to use them without seeing their code.
Learning objectives
Identify the attributes and behaviors of a class found in the libraries contained in an API.
Libraries, packages, and APIs
A library is a collection of classes. Related classes are grouped into packages; for example, String and Math are in java.lang, which every program can use without an import. ArrayList, Scanner, and File live in packages you import (java.util, java.io).
An API (Application Program Interface) specification lists each class's constructors and methods: their names, parameters, return types, and what they do.
Attributes and behaviors
Every class defines attributes (the data each object stores, held in variables) and behaviors (what objects can do, defined by methods). Reading documentation means identifying both.
Class
Attributes
Behaviors
String
The sequence of characters
length(), substring, indexOf, equals
ArrayList
The list of elements
add, get, set, remove, size()
A BankAccount class
owner, balance
deposit, withdraw, getBalance
Key points
Libraries are collections of classes; an API specification explains how to use them.
A class defines a reference type. Classes are grouped into packages.
Attributes are data stored in variables. Behaviors are actions defined by methods.
Watch out
You can use a class correctly from its documentation alone. On the exam, read the provided method descriptions carefully instead of guessing what a method does.
Exam tip
The Java Quick Reference you get on exam day is a small API. Know where each method is so you can look it up quickly.
Quick check
In a Song class with title, artist, and a play() method, which are attributes and which are behaviors?Show answer
title and artist are attributes; play() is a behavior.