simulation and example. simulation simulation is used to study the performance of a physical system...

Simulationand Example

SimulationSimulation is used to study the

performance of a physical system by using a physical, mathematical, or computer model of the system

Steps to take when you do simulation◦Algorithm◦Programming techniques and coding◦Testing

Example Write a program that simulates the operation of a busy

airport that only has one run way to handle takeoff and landings. You may assume that each takeoff or landing takes 15 minutes to complete. One runway request is made during each 5 minute time interval and the likelihood of a landing request is the same as for a takeoff request. Priority is given to planes requesting a landing. If a request can not be honored, it is added to a takeoff or landing queue. This program should simulate 120 minutes of activity at the airport. Each request for runway clearance should be time-stamped to the appropriate queue. The output from your program should include the final queue contents, the number of takeoffs completed, the number of landings completed and the average number of minutes spent in each queue

Part 1: Determine Main Algorithm

Clock =0Total time =

120Time done=0

Clock < Total time?

No

Yes

Toss a coin

Head?

stopStar

t

Check landing arrival

Check takeoff arrival

Current serve done?

Serve the next one

Yes

Clock += 5

No

No

Yes

Part 2: Determine main data structureQueue:

◦Takeoff◦Landing

That queue has every attribute/action that a normal queue has and the following special attributes/actions◦Number of takeoff or landing served◦Total time wait◦Check new arrival in landing or takeoff

queues◦Update statistics

Part 2: Determine main data structureRequest:

◦processingTime◦arrivalTime◦(may be requestID)

Part 3: Make the main algorithm more specificCheck takeoff or landing arrivalGiven an arrival

timeCreate a new

request

Print status for each queue

Part 3: Make the algorithm more specificServe the next one

Landing queue is

NOT empty

currentRequest = get the first element in the landing queue

Timestamp = get arrival time of

current request

Wait =current clock -

timestamp

TotalWait +=waitNumber of landing/takeoff

served ++

YesTakeoff

queue is NOT

empty

Current request =

get the first request in the takeoff

queue

Yes

No

No

The run way is idle now

ImplementationClasses:

◦Queue (Using Lab3Queue with just a little bit change in Lab1LinkedList)

◦Request◦RunawayQueue (extends from

Queue)◦AirportSim that actually starts the

simulation and contain the main algorithm.

TestingDiscussion:

◦How can we test this simulation program:

◦Criteria: Robustness: not crashing Accuracy: correctly computed

TestingUnit test

◦Make sure Queue is working, RunawayQueue is working and Request is working correctly

Integration test◦Test if AirportSim is working correctly

Leave a trace of execution by displaying the method name as you enter it

Display values of all input parameters upon entry to a method

Chapter 2: Program Correctness and Efficiency 13

Testing ProgramsThere is no guarantee that a program

that is syntax and run-time error free will also be void of logic errors

The “best” situation is a logic error that occurs in a part of the program that always executes; otherwise, it may be difficult to find the error

The worst kind of logic error is one that occurs in an obscure part of the code (infrequently executed)


Structured WalkthroughsMost logic errors arise during the design

phase and are the result of an incorrect algorithm

Logic errors may also result from typographical errors that do not cause syntax or run-time errors

One form of testing is hand-tracing the algorithm before implementing

Structured walkthrough: designer must explain the algorithm to other team members and simulate its execution with other team members looking on


Levels and Types of TestingTesting: exercising a program under

controlled conditions and verifying the resultsPurpose is to detect program defects after all

syntax errors have been removed and the program compiles

No amount of testing can guarantee the absence of defects in sufficiently complex programs

Unit testing: checking the smallest testable piece of the software (a method or class)

Integration testing: testing the interactions among units


Levels and Types of Testing (continued)System testing: testing the program in

contextAcceptance testing: system testing

designed to show that the program meets its functional requirements

Black-box testing: tests the item based on its interfaces and functional requirements

White-box testing: tests the software with the knowledge of its internal structure


Preparations for TestingA test plan should be developed early in

the design phaseAspects of a test plan include deciding how

the software will be tested, when the tests will occur, who will do the testing, and what test data will be used

If the test plan is developed early, testing can take place concurrently with the design and coding

A good programmer practices defensive programming and includes code to detect unexpected or invalid data


Testing Tips for Program SystemsMost of the time, you will test program systems

that contain collections of classes, each with several methods

If a method implements an interface, its specification should document input parameters and expected results

Carefully document each method parameter and class attribute using comments as you write the code

Leave a trace of execution by displaying the method name as you enter it

Display values of all input parameters upon entry to a method


Testing Tips for Program Systems (continued)Display the values of any class

attributes that are accessed by this method

Display the values of all method outputs after returning from a method

Plan for testing as you write each module rather than after the fact


Developing the Test DataTest data should be specified during the

analysis and design phases for the different levels of testing: unit, integration, and system

In black-box testing, we are concerned with the relationship between the unit inputs and outputs◦There should be test data to check for all expected

inputs as well as unanticipated dataIn white-box testing, we are concerned with

exercising alternative paths through the code◦Test data should ensure that all if statement

conditions will evaluate to both true and false


Testing Boundary ConditionsWhen hand-tracing through an

algorithm or performing white-box testing, you must exercise all paths

Check special cases called boundary conditions


Why do Testing?Normally testing is done by

◦The programmer◦Other members of the software team who did

not code the module being tested◦Final users of the software product

Do not rely on programmers for testing as they are often blind to their own oversights

Companies also have quality assurance organizations that verify that the testing process is performed correctly

In extreme programming, programmers work in pairs where one writes the code and the other writes the tests


StubsIt may be difficult to test a method

or class that interacts with other methods or classes

The replacement of a method that has not yet been implemented or tested is called a stub

A stub has the same header as the method it replaces, but its body only displays a message indicating that the stub was called


DriversA driver program declares any

necessary object instances and variables, assigns values to any of the method’s inputs, calls the method, and displays the values of any outputs returned by the method

You can put a main method in a class to serve as the test driver for that class’s methods


Using a Test FrameworkA test framework is a software

product that facilitates writing test cases, organizing the test cases into test suites, running the test suites, and reporting the results

A test framework often used for Java products is JUnit, an open-source product that can be used in a stand-alone mode and is available from junit.org


Debugging a ProgramDebugging is the major activity

performed by programmers during the testing phase

Testing determines if there is an error, debugging determines the cause of it

Debugging is like detective work◦Inspect carefully the information displayed

by your program◦Insert additional diagnostic output

statements in the method to determine more information


Using a DebuggerDebuggers often are included with IDEsA debugger can execute your program

incrementally rather than all at onceSingle-step execution executes in

increments as small as one program statement

Breakpoints are used to traverse large portions of code before stopping

The actual mechanics of using a debugger depend on the IDE that you are using


Using a Debugger (continued)


Reasoning about Programs: Assertions and Loop InvariantsAssertions: logical statements about

a program that are claimed to be true; generally written as a comment

Preconditions and postconditions are assertions

A loop invariant is an assertion◦Helps prove that a loop meets it

specification◦True before loop begins, at the beginning

of each repetition of the loop body, and just after loop exit


Efficiency of AlgorithmsDifficult to get a precise measure of the

performance of an algorithm or programCan characterize a program by how the

execution time or memory requirements increase as a function of increasing input size◦Big-O notation

A simple way to determine the big-O of an algorithm or program is to look at the loops and to see whether the loops are nested


Efficiency of Algorithms (continued)

simulation and example. simulation simulation is used to study the performance of a physical system...

Documents

queue slide

types of testing testing

system testing

coding testing slide

simulation program

takeoff request

landing request

form of testing