Software dev midterm

waterfall process model

• requirements

• design

• implementation

• verification

• maintenance

6 reasons for project failure

• functionality issues

• substantially late

• quality issues

• high cost variance

• canceled after launch

• rejected or not implemented for other reasons

three steps in a SW project

• analysis

• design

• implementation

what superseded the waterfall model?

Agile Software Development, managed by Scrum

• build software incrementally

• use short 1-4 week iterations

• keep development aligned with changing needs

ISA

• instruction set architecture

• machine code

compiled languages

• translated into machine code ahead of time by the compiler

• compiler produces an executable file that runs directly on the CPU

• fast and efficient at run time

• must be recompiled separately for each machine architecture/OS

interpreted langauge

• code is read and executed line by line by an interpreter

• can move the same program between different systems and run it unchanged

• slower since each instruction is translated at runtime

java language

• compiles into java bytecode and runs on a Java Virtual Machine

• that same bytecode can be run on any machine with a JVM

• JVM uses a JIT (just in time) compiler, which watches which parts of the code run a lot, then compiles those hot spots into machine code (pretranslated)

• portability of interpreted languages + efficiency of compiled languages

Local Version Control System

• database of changes on local computer

• delta base version control

• stores a base version and then only saves the specific changes for each version

• no collaboration

• example: revision control system

Centralized Version Control System

• entire version database is stored on a central network server

• supports collaboration

• workflow:

  • sync with VCS server

  • update to latest version from VCS

  • work on local version

    • commit changes to VCS (after potential conflict resolution)

• single point of failure

  • if a server goes down, no one can save their work

Distributed Verson Control System

• everyone gets a clone of the repository, including its full history

• if central server crashes, repository can be restored from any local copy

• workflow:

  • commit: save changes to local repository history

  • push: to share local commits to the upstream repository

• Git is the actual software

• Github provides the central repository

Git

• series of snapshots of a miniature file system

• no duplicate files as snapshots share references to identical files

• operations are local because I have a fully copy of snapshots and history

• checksum SHA-1 Hash key used as id for files/folders

Git: 3 states for a file

• committed: data is safely stored in the local database

• modified: file changed but not yet committed to local database

• staged: modified file is marked in its current version to go into the next commit snapshot

trunk(green)

• main line of development

• Git: “master” branch (default) or main branch

tag(blue)

release, a full snapshot of a version that is not supposed to be changed

branch (yellow)

• side tracks to the trunk line that results from maintenance, bug fixes of released versions, or as a general stratedgy to support team work and concurrent development

• merging occurs if one wants to incorporate improvements from a branch into the trunk

hardware has separate units for integer and floating point arithmetic

• basic types for discrete numbers: integer, short, long integer

• basic types for floating point: float, double precision

program counter (PC)

• special register in the CPU that holds the memory address of the very next instructions to be run

• After the CPU finishes an instruction, the PC increments to the next address (pc + 1)

heap

• large, less structured pool of memory available

• memory can be allocated (requested) and deallocated (released) at runtime

• garbage collection

  • finds any objects on the heap that are no longer being used by the program and frees memory

• Java’s type system tells the program how to interpret raw bit patterns

• it is important to initialize variables bc it might contain leftover garbage

• Dynamic data structures

  • it can always request more memory from the heap as it grows

volatile memory

• short-term memory that requires constant power to maintain its data, losing everything when the device is turned off

• RAM

• CPU cache

• main memory

persistent memory

• long term storage that retains its data after power is turned off

• SSD, hard drive

object-oriented programming

a paradigm that bundles data (attributes) and the functions that operate on that data(methods) into a single unit called an object

encapsulation

practice of hiding an object’s internal data and complexity, exposing only safe, public methods for interaction

polymorphism

• the ability to treat objects of different types as if they are the same, as long as they share a common role/interface

• allows for flexible and reusable code

• ability to select different methods (of same signature) according to the actual type of an object

package

• a mechanism for organizing related classes and interfaces into a group/namespace

• implemented as sub directories on the file system

class

• fundamental coding unit

• can only have one public class per file

• it is reccomended to give each class its own file

non static method

• belongs to a specific instance of a class

• works w/ the unique data (attributes) of that instance

• must create an object first to be able to call the method

static method

• belongs to the class itself, not to any one object

• a general function that doesn’t depend on the state of a specific instance

• can call it directly on the class without ever creating an object

try{

}

finally{

}

• guaranteed to execute after the try block, regardless of whether an exception was thrown or not

• primary purpose is for resource cleanup, such as closing files or network connections

unchecked exception

• represent a bug/logical error

• things the programmer could have and should have prevented

• the compiler doesn’t check to see if you handle them

• NullPointerException

• ArrayIndexOutOfBoundsException

checked exception

• expected probemems with external resources that a correct program might encounter

• compiiler checks your code and forces you to acknowledge that this error might happen and have a plan for it

• if you call a method that is declared to throw a checked exception, you have to handle it with a try-catch or a throw

• IOE exception - if a file is deleted or network connection is lost

primitive type

• value is stored directly in memory

• byte, short, int, long, float, double, char, and boolean

tokenization

• the process of splitting a string into a sequence of smaller strings, called tokens

• based on a separater called a delimiter

hasMoreTokens()

• boolean method that returns true if there are more tokens left to process

• used as the condition for a while loop

nextToken()

returns the next token as a string and advances the internal cursor

countTokens()

returns the number of tokens remaining to be processed

parseInt()

static method that takes a string and returns the corresponding int

call stack

• stores local variables for primitive types

• for object types (String, ArrayList) : stores a reference that points to where the actual object lives on the heap

object state

• constructor establishes a valid initial state

• an object can use its state to control the order in which its methods are called

interface

• a contract that defines a set of abstract method signatures

• what a class must do, not how

• a class that uses “implements” promises it will provide the code for all methods in the interface

• enables polymorphism, allowing to write code that works with any object that fulfils the contract

static field

• a variable that is shared across all instances of a class

• only one copy of a static variable, no matter how many objects you create

constant

• static final

• only one instance of this variable associated with the class

• its value can never be changed after it is initalized

what is the superclass of all objects?

java.lang.Object

HashMap

• a data structure that stores key-value pairs

• uses a key’s hashCode() to find the correct array index for storing/retrieving a value

• then uses equals() to find the exact key in the bucket, which is needed to handle hash collisions

• if two objects are equal, they must have the same hash code

superclass

• you can use a subclass object whenever a superclass object is expected

• a subclass method can’t be more demanding/stricter about its inputs then its parent method

• user super.method() to call a method from your direct parent class

• climbs are just one level in hierarchy

• For constructors:

  • super() used to call a constructor from the direct parent class

  • it must be the 1st statement

  • if a subclass constructor doesn’t call super, the superclass must have a constructor with no parameters

SOLID principles in OO Design

• S: single responsibility principle

  • class should only have one responsibility

  • concerns: effect of changes, complexity of a class, class reuse

• O: Open/Closed principle

  • software entities should be open for extension, closed for modification

  • concerns: inherit from abstract base classes, keep interface fixed

• L: Liskow’s substitution principle

  • objects in a program should be replaceable w/ instances of their subtype w/o altering the correctness of the program

• I: interface segregation principle

  • many client-specific interfaces are better than one general-purpose interface

• D: dependency inversion principle

  • depend upon abstractions

  • don’t depend on concretions

The percentage of large software development projects (budget exceeds $1M) that fail is in the following range (based on a Gartner study of 2012)

20-40%

what is method signature?

• method name

• parameter list

java primitive types

• byte

• short

• int

• float

• long

• double

• boolean

• char

Wrapper classes

• Byte

• Integer

• Short

• Double

• Long

• Float

• Boolean

• Character