Java

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Object

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An entity with states(fields) and behavior(shown via methods)

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Class

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blueprint for an object. contains fields and methods that describe the behavior of an object

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Types a variables

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Local - declared inside a method, destroyed when method is completed

Instance - declared inside a class, but outside any method

Class - declared inside of a class, static

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Constructor

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gets invoked when an object is created. sets state (fields) of object.

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Static

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Keyword. static variables can be called upon without an instance of its class being created. all instances of class share the same variable

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Access modifier

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sets access levels for classes, variables, methods, constructors. public, private, protected, default

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Interface

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An interface is a collection of abstract methods. A class implements an interface, thereby inheriting the abstract methods of the interface.

interfaces do not provide any implementation, they are only meant to be implemented. sets up a contract for a class to conform to

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scope

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refers to section of code where variable can be accessed

REFACTOR

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Overriding

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when a class has the same method as its parent class, but the method body is different.

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Overloading

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when methods are in the same class with the same name but take in different types and/or different number of argugments

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reflection

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code examining itself.

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Encapsulation

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hiding data

the technique of making the fields in a class private and providing access to the fields via public methods.

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Nested Class

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static inner class

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Downcasting

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when you treat a parent class as a child class

Animal animal = new Animal()

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Super

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keyword used to refer to the immediate parent class

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primitive datatypes

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int, byte, short, long, boolean, double, float, character.

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Abstract class

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keyword used to specify that a class should not be instantiated. it is only used to be extended by other classes

has no implementation

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Argument

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data item specified in a method call

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array

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A collection of data items, all of the same type.

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casting

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conversion from one datatype to another

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Enumerated type

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type whose legal values consist of a fixed set of constants

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exception

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an event during program execution that prevents the program from continuing normally

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exception handling

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a mechanism that handles exceptions to keep the program running normally

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throw vs throws

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throw is a keyword that allows the user to throw an exception.

throws is keyword used in a method declaration that specify which exceptions could be thrown

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what is a checked exception

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any exception that is caught by the compilerbefore run time.

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Inheritance

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when a sub class acquires the properties of its parent class

Is a relationship

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Composition

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When you put an object inside another object. Has a relationship

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SOLID principles

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5 principals of Object Oriented Design

Single responsibility - a class should only have one job

Open closed - a class should be https://www.google.com/search?client=ubuntu&channel=fs&q=are+exception+runtime+erroreasily extended without modifying the class itself

Liskov substitution - every subclass should be substitutable with there parent class

Interface segregation - a client should not be forced to use a method or interface they dont use

Dependency Inversion - allows for decoupling

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variable

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used to store and manipulate data

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implicit conversion

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compiler will automatically convert a type into a higher type

int > long

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casting

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manually converting one type to another type

(int) long

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.this

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used when refering to the current object, allows object to pass itself as a parameter

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null

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refers to an uncreated object

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types of test

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System - testing the application as a whole

aggregate - testing component (series of classes / methods)

unit - testing a single unit of functionality (single method / class with single responsibility)

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test driven development

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Software dev process of writing test before writing code. using test to help guide the design process

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test structure

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Given - establish the preconditions for the test

When - what is being tested

Then - checking the outcome

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polymorphism

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the ability of an object to take multiple forms

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abstraction

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technique of hiding implementation details from the user and only providing them with functionality

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Wrapper class

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used to convert a primitive type to a class

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Boxing

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converting a primitive to a class

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Concurrency

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multiple threads running at the same time working with the same resources

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multithreading

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enables complete use of cpu. when multiple threads run at the same time.

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thread

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a sequence of programmed instructions

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process

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an instance of a program. has memory and atleast one thread