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Published byNathan Parks Modified over 9 years ago
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By : Robert Apeldorn
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What is OOP? Object-oriented programming is a programming paradigm that uses “objects” to design applications and computer programs
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Terms needed to know Class blueprint or prototype from which objects are created Object data structures consisting of data fields and methods together with their interactions Inheritance "Subclasses" are more specialized versions of a class, which inherit attributes and behaviors from their parent classes, and can introduce their own. Interface group of related methods with empty bodies Package namespace that organizes a set of related classes and interfaces
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Objects An object stores its state in fields and exposes its behavior through methods Methods operate on an object's internal state and serve as the primary mechanism for object-to-object communication
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Example of a bicycle
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Pros with Objects Modularity The source code for an object can be written and maintained independently of the source code for other objects Information-hiding By interacting only with an object's methods, the details of its internal implementation remain hidden from the outside world Code re-use If an object already exists, you can use that object in your program. This allows specialists to implement/test/debug complex, task-specific objects, which you can then trust to run in your own code Pluggability and debugging ease If a particular object turns out to be problematic, you can simply remove it from your application and plug in a different object as its replacement
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Classes The basic structure of Java programs with user defined classes: public class ClassName { public static void main(String[] args) { program statements } user defined methods } user defined classes
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Class Definitions Constructors special block of statements called when an object is created, either when it is declared or when it is dynamically constructed on the heap through the keyword “new” Methods consists of a sequence of programming statements to perform an action Field data member of the class
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Different Class Modifiers Public Can be accessed outside the program Private Cannot be accessed outside of the current class Protected A subclass can directly access a superclass Ex) subclass square can access class shape
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Example of a Class class Bicycle { int cadence = 0; int speed = 0; int gear = 1; void changeCadence(int newValue) { cadence = newValue; } void changeGear(int newValue) { gear = newValue; } void speedUp(int increment) { speed = speed + increment; } void applyBrakes(int decrement) { speed = speed - decrement; } void printStates() { System.out.println("cadence:"+cadence+" speed:"+speed+" gear:"+gear); }
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Inheritance
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How to use inheritance Class MountainBike extends Bicycle { //properties of mountain bike }
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Interface example public interface Bicycle { void changeCadence(int newValue); // wheel revolutions per minute void changeGear(int newValue); void speedUp(int increment); void applyBrakes(int decrement); }
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How to implement the interface Class ACMEBicycle implements Bicycle { // remainder of this class implemented as before }
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Sources “Java OOP basics” http://www.cs.drexel.edu/~knowak/cs265_fall_2 009/java_OOP_and_%20inheritance.pdf The Java Tutorials. Trail: Learning the Java Language. Oct 19, 2009.
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