toblick / cs101 / exam 2 review

class: center, middle # Exam 2 Review Intro to Computer Science --- # Agenda 1. [ArrayList](#arraylist) 1. [Multidimensional Arrays](#multidimensional-arrays) 1. [Object-Oriented Programming](#oop) 1. [Pillars](#pillars) 1. [Patterns](#patterns) 1. [Strings](#strings) 1. [Inheritance](#inheritance) 1. [This is Super](#this-super) 1. [Conclusions](#conclusions) --- name: structure # Structure -- name: arraylist # ArrayList -- ## Main themes - a class in the Java API (i.e. `java.util.ArrayList`) - behaves similarly to the fundamental primitive array data structure, but has a malleable length and stores only objects - easy to `add()`, `remove()`, and `get()` objects to/from an `ArrayList`. - odd syntax, e.g. `ArrayList<Alien> = new ArrayList<Alien>()`, which we won't talk about (called Java "generics" or parameterized types) --- name: multidimensional-arrays # Multidimensional Arrays -- ## Main themes - Arrays of arrays - Two-dimensional arrays can be visualized as tables with rows and columns - first dimension is like the rows - second dimension is like the columns - Declaring, allocating, and assigning values - Looping through multi-dimensional arrays - the "standard" way using nested counter-based loops - using the **foreach** type of loop (e.g. `for (String[] val : values) { /* ... */ }`) - Ragged arrays exist - Passing arrays as arguments to methods --- name: #oop # Object-Oriented Programming -- ## Main themes Basic object-oriented programming - Classes are essentially custom data types. - Classes are reference types in Java. - Objects are instances of a class. - Defining a class - Constructors - Instance methods and properties - Static methods and properties - Instantiating an object --- name: patterns # Patterns ## Main themes: - `private` for instance properties and methods - Getters and setters to provide public access for `private` properties, where desired - Perform validation in setters - Always use those setters, even within the same class file - Overloaded methods and contructors provide multiple variants of the same action - `static` for shared properties and methods - `final` for values that never change (final variables can be initialized only once) - Inheritance vs. composition --- name: strings # Strings -- ## Main themes: - `String` is a class in the Java API, not a fundamental primitive data type. - because different objects are stored at different locations in memory, compare the value of two `String` objects with its custom `.equals()` method, not `==`. - `String` is designed following the principle of object-oriented abstraction (e.g. `.length()` rather than `.length`) - Encapsulated within every `String` is a `char` array. --- name: inheritance # Inheritance -- ## Main themes: - Child classes inherit properties and methods of parent classes, except... - `private` properties and methods are not inherited... - ...but `private` properties are still accessible via any inherited `public` getters and setters - `protected` properties and methods are accessible from subclasses (those can be in other packages, too) - constructors are not inherited, but are accessible via the `super` keyword - Use of the `super` keyword to refer to code belonging to the parent class -- - Motivations: readability, modularity, avoiding code duplication, ... --- template: inheritance ## Polymorphism Polymorphism goes hand-in-hand with inheritance. - Child objects can be considered to be of their parent class. - e.g., if `B` inherits from `A`, then a `B` object can be referred to as both a `B` and an `A` object. - Can be useful when storing objects of a variety of child types into a single array typed as the parent type. - This allows you to easily loop through them all. - `instanceof` operator allows you to check whether an object is of a given type. --- name: this-super # This is Super -- ## Main themes: - the `this` keyword, when used within a method, refers to the object upon which that method was called. - you cannot use the `this` keyword within a `static` method, since that method can never be called on an object. - the `super` keyword, when used within a method, refers to code in the parent class. - a call to the parent class's constructor can be added to a child class constructor, if useful (e.g. `super()` or `super(someArgs)`) ---