1 Code Quality, Maintainability, Reusability, Debugging, Testing SIF8080, Sep. 27th 2001...

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Code Quality, Maintainability, Code Quality, Maintainability, Reusability, DebuggingReusability, Debugging, Testing, Testing

SIF8080, Sep. 27th 2001

Customer-driven project

Carl-Fredrik Sørensen mailto:[email protected]

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Spider-webSpider-web::theoretical

::pck_stream

::pck_cargo

::choke

::lift_account

::pck_stock

::pck_cargo_doc

::units

::lagkodeserver

::pck_check

::pck_stream_network

::pck_well

::sep_test

::pck_flowline

::pck_facility

::pck_system

::mathlib

::pck_regression

::calc_stream::comp_analysis::regularity

::well_node

::puf

::summarise

::tbp_product

::transfer_basis

::value_adjust

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OutlineOutline

Code Quality & Standards.Debugging, logging etc.Debugging, logging etc.Testing.Testing.

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Key Principles; CodingKey Principles; Coding

UnderstandabilityHigh cohesionLoose couplingCode FormattingConsistent Naming Information hiding Valuable Comments

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Code Standards (1)Code Standards (1)

Why?– Gives less defects.– Easier/cheaper maintenance.– Several people may work on and understand the same

code.– Code to be read, not only written.

Java coding standards:– The Elements of Java Style; Vermeulen et.al. SIGS Books.– http://java.sun.com/docs/codeconv/html/CodeConvTOC

.doc.html.

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General rules:– Simplicity – Build simple classes and methods.

Keep it as simple as possible, but not simpler (Einstein).

– Clarity – Ensure item has a clear purpose. Explain where, when, why, and how to use each.

– Completeness – Create complete documentation; document all features and functionality.

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General rules (continued):– Consistency – Similar entities should look and

behave the same; dissimilar entities should look and behave differently. Create and apply standards whenever possible.

– Robustness – Provide predictable documented behaviour in response to errors and exceptions. Do not hide errors and do not force clients to detect errors.

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Do it right the first time !Your professionalism is expressed by applying

code standards !Document any deviations!

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FormattingFormatting

Is important for readability, not for the compiler.

Use a common standard for code formatting.Do not alter the style of old code to fit new

standards.

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Examples (1)Examples (1)

class MyClass {

void function (int arg) {

if (arg < 0) {

for (int index = 0; index <= arg; index++) {

//… Some Action Code …

} // end for

} // end if

} // end function

} // end MyClass

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Examples (2)Examples (2)

Include white space:– Bad: double length=Math.sqrt(x*x+y*y);– Better: double length = Math.sqrt(x * x + y * y);– Use blank lines to separate.– Do not use hard tabs.

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NamingNaming

Clear, unambiguous, readable, meaningful. Describe the purpose of the item:– Bad: X1, X2, mth, get, tmp, temp, result.– Give a descriptive name to temporary variables.

But: scientific formulas may be better formulated with single characters/words representing symbols instead of descriptive names.

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NamingNaming

Establish and use a common naming convention. Problems creating a good name purpose of the

operation is not clear.– Bad: void get(…)., better: retrieveDataSamples.– Bad: Time day(Time p_day), better: getDate or

getTruncDate.– Bad: void result(…), better: createResults.– Bad: void gas/oil/water, better: calculate…VolumeRate.

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Java Java Naming ConventionNaming Convention

Package: scope.mypackageClasses: MyClassMethods: myMethodConstants: MY_CONSTANTAttribute: myAttributeVariable: myVariable

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ParametersParameters

Actual parameters should match the formal Input-modify-output order If several operations use similar parameters, put the

similar parameters in a consistent order Use all parameters Document interface assumptions about parameters

– access type, unit, ranges, non-valid values

Limit the number of parameters to about seven

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CommentsComments; ; Why, when, where, Why, when, where, what what

Why: To be able to find out what a operation does after a half, one or two years. Automatic API documentation.

When; Document your code before or when you write it; Design before you implement. Put the design in the operation.

Where; Before the operation, at specific formulas, decision points etc.

What; Document the algorithm, avoid unnecessary comments. Refer to a specification if existing.

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JavaDoc (1)JavaDoc (1)

Generates HTML-formatted class reference or API documentation.

Does only recognise documentation comments that appear immediately before– class– Interface– constructor, – method – field declaration.

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Purpose: To define a programming contract between a client and a supplier of a service.

Keep the documentation synchronised with the code. MAKE DOCUMENTATION FIRST, then code!

JavaDoc tags:– @author, @version, @see, @param, @return, @exception.– {@link}.

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JavaDoc Example: Class JavaDoc Example: Class

/**

* <code> MyConstants </code> is the base class for all the constants and

* implements any general constant responsibilities.

*

* @author Carl-Fredrik Sørensen

* @version $Revision: 1.0$

* @invariants p > 0

*

* @see MySpecificConstants

*/

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Document pre-, post- and invariant conditions (OCL…).– @pre-condition, @post-condition, @invariants.

Document known defects and deficiencies.– @defect.

Document synchronisation semantics.

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JavaDoc Example: Method JavaDoc Example: Method

/**

* Method description

*

* @param paramName Name of the mechanism to search for,

* one of the constants in the <code>MyClass</code> class.

* @return The concrete instance of an <code>MyClass</code>

* that is currently in effect if one found, null if not.

* @exception Throwable Default finalizer exception.

* @pre-condition valid paramName.

* @post-condition (… described in @return here…)

*/

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Architecture; How to Avoid Architecture; How to Avoid Spider-webSpider-web

Class/package organisation (loose coupling, high cohesion):– Split classes in (package/service) layers (user, data and

business). Use package scoping (no.ntnu.idi…..).– Uni-directional dependencies.

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Refactor to a New ArchitectureRefactor to a New Architecture

::EcBpStreamFlare

::EcDpStream ::EcDpWellReservoir

::EcBpStreamFluid::EcBpStreamShipper ::EcDpWellStream

::EcDpStreamFluid::Theoretical

::EcBpStream::EcDpDerivedStream

::calc_stream

::comp_analysis

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Information HidingInformation Hiding Do not expose operations that should be local to a

package. Hide data access from the business services.

– Create separate packages for performing data services.– Define interfaces for data access, like e.g. EJB.

Scoping:– public: classes exposed by interfaces, operations in

interfaces.– package: classes and operation not exposed through

interface, but used by other classes in package.– private: local attributes and methods.

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Information HidingInformation Hiding

Hide the action part in control structures (functional cohesion) if complex, else delegate to a method.

What to hide:– Areas that are likely to change; hardware dependencies,

input/output, non-standard language features, difficult design and implementation areas, data-size constraints, business rules, potential changes.

– Complex data.– Complex logic.

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BindingBinding

Bind constants as late as possible– Do not use magic Numbers, avoid hard-coded values

totalFooDay = totalFooHour * 24;

if (me.equals(”thirsty”)) return ”water”;

– Avoid global variables (constants OK)– Use separate classes/methods to hide hard-coded values

Achieves faster maintenance, and avoids copy-paste errors Makes code better suited for reuse Static methods and/or constants

MyConstants.C1_SPECIFIC_GRAVITY

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Java Exceptions (1)Java Exceptions (1)

Unchecked run-time exception: serious unexpected errors that may indicate an error in the program’s logic Termination.

Checked exception: errors that may occur, however rarely, under normal program operation The caller must catch this exception.

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Java Exceptions (2)Java Exceptions (2)

Only convert exceptions to add information. If the method does not know how to handle an exception it should not be handled.

Do not silently absorb a run-time or error exception makes code very hard to debug.

Use finally blocks to release resources.

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Code Defensively (1)Code Defensively (1)

Check input data for validity (Pre-conditions).– Range, comment assumptions about acceptable input ranges

in the code.– Use a general approach for error handling when erroneous

data. Use exception handling only to draw attention to

unexpected cases (Do NOT perform any processing in exception code) (invariants).

Anticipate changes; Hide to minimise impact of change.

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Code Defensively (2)Code Defensively (2)

Introduce debugging aids early (logging).Check function return values (post-conditions).Return friendly error messages; Write to a log

file any system specific error messages (IO/SQL Exceptions, error codes etc.).

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SummarySummary

Remember your code should be understandable.Maintenance is often up to 70% of a total

project cost.Use quality control.

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OutlineOutline

Code quality and Code Standards.Code quality and Code Standards.Debugging, logging etc.Testing.Testing.

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DebuggingDebugging

Single thread/process.– IDE’s with debugger most often sufficient.

Multiple clients, threads, distributed applications.– Synchronisation issues to protect the state of objects.– IDE’s (most often) lack good support.– Pre-instrumentation of code is often necessary.

Non-visual services (e.g. Real-time data conversions).– May debug single runs in IDE’s.– Hard to debug in real settings: system runs continuously or

discretely at fixed times

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Application Logging: What Application Logging: What and Why?and Why?

An application log is a text history of notable events logged by your application.

The logs helps you to figure out what went wrong (and right) during the execution of your application.

With the advent of N-tier architectures, Servlets, JSPs, and EJBs, application logging is particularly important to report errors that cannot or should not be surfaced to the user interface.

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JLog – Java Logging FrameworkJLog – Java Logging Framework

Developed by Todd Lauinger.A significant event happens in your Java code.

That event could be any of several different types and conditions. Before you start using a logging framework:– categorize and document your events so that all

users of the framework will log events consistently.

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System Event CategoriesSystem Event Categories

Levels:– CRITICAL_ERROR. (Highest - 1)– ERROR.– WARNING.– INFORMATION.– DETAIL.– TRACE. (Lowest - 6)

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Logging GranularityLogging Granularity

Agreed and documented set of event categories determine the granularity to log those events.

Separate logs for e.g.– thread pool.– SQL processor.

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Logging EventsLogging Events

Instrument code with logging statements: – AppLog.criticalError("Caught unexpected

exception: " + e);– SQLLog.info("Executing SQL query: " +

statement);– AppLog.trace("Entering method

getName()"); Notice: the code does not need to have any "if"

logic.

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Configuring the LogsConfiguring the Logs (1) (1)

Configuration from a properties file.LogFileExtension = log LogFilePath = c:\\temp\\ LoggingLevel = 2 LoggingMechanism = log.StandardErrLoggingMechanism LogFieldSeparator = |

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You may select the output logging level. Default is the INFO level.

All events logged at a level less than or equal to the log's current logging level will be output to the logging mechanisms.

Events logged at a numerically higher level (i.e., a less critical level) will be discarded.

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At runtime, you can increase or decrease the logging level of any of your logs without affecting your other logs.

If you are trying to debug a nasty problem with your thread pool, you can programmatically change the log at runtime :

ThreadLog.getInstance().setLoggingLevel(Log.TRACE_LEVEL);

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Other ways to dynamically reset the logging level at runtime:– In a debugger, you can change the value of the log's

currentLoggingLevel variable.– In an application server, you can examine and manipulate

log properties with some JSPs.– Use RMI to manipulate the log properties of a remote JVM.– There are more options you can configure both

programmatically and via a properties file.

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Reading the Logs (1)Reading the Logs (1)

Sample entries from a shared log, a vertical bar ( | ), is used to delimit the various fields of log entries:

RequestLog|L4|09:32:23:769|ExecuteThread-5|Executing request number 4

SQLLog|L4|09:32:23:835|ExecuteThread-5|select * from Customer where id = 35.

RequestLog|L4|09:32:23:969|ExecuteThread-5|Request 4 took 200 milliseconds.

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Reading the Logs (2)Reading the Logs (2)Import the log into a spreadsheet:

– ASCII text import with a vertical bar as a field delimiter.

– Sort or filter the log using various spreadsheet capabilities.

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Primary JLog Classes and Primary JLog Classes and RelationshipsRelationships

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OutlineOutline

Code quality and Code Standards.Code quality and Code Standards.Debugging, logging etc.Debugging, logging etc.Testing.

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TestingTesting

Not closely integrated with development prevents measurement of the progress of development - can't tell when something starts working or when something stops working.

JUnit to cheaply and incrementally build a test suite that helps to:– measure your progress,– spot unintended side effects.– focus your development efforts.

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JUnitJUnit

Automatic testing framework.– Acceptance tests.– Integration test.– Unit test.

Reports the number of defects graphically.May create many tests for each method.

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JUnit ExampleJUnit Example

Pay attention to the interplay of the code and the tests.– The style: to write a few lines of code, then a test

that should run, – or even better: to write a test that won't run, then

write the code that will make it run. The program presented solves the problem of

representing arithmetic with multiple currencies.

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Example: MoneyExample: Moneyclass Money {

private int fAmount; private String fCurrency; public Money(int amount, String currency) {

fAmount= amount fCurrency= currency;

} public int amount() {

return fAmount; }

public String currency() { return fCurrency; }}

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JJUUnitnit

JUnit defines how to structure your test cases and provides the tools to run them.

You implement a test in a subclass of TestCase.

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Example: MoneyExample: Money

public Money add(Money m) {

return new Money(amount()+m.amount(), currency());

}

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JunitJunitDefine MoneyTest as a subclass of TestCase. Put MoneyTest in the same package as the

classes under test access to the package private methods. – Add method testSimpleAdd, that will exercise the

simple version of Money.add() above. – A JUnit test method is an ordinary method without

any parameters.

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Example: MoneyTestExample: MoneyTest

public class MoneyTest extends TestCase {

//…

public void testSimpleAdd() {

Money m12CHF= new Money(12, "CHF"); // (1)

Money m14CHF= new Money(14, "CHF");

Money expected= new Money(26, "CHF");

Money result= m12CHF.add(m14CHF); // (2)

assert(expected.equals(result)); // (3)

}

}

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Developing TestsDeveloping Tests

public void testEquals() {



assert(!m12CHF.equals(null));

assertEquals(m12CHF, m12CHF);

assertEquals(m12CHF, new Money(12, "CHF")); // (1)

assert(!m12CHF.equals(m14CHF));

}

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Developing TestsDeveloping Testspublic boolean equals(Object anObject) {

if (anObject instanceof Money) {

Money aMoney= (Money)anObject;

return aMoney.currency().equals(currency())

&& amount() == aMoney.amount();

}

return false;

}

Override the method hashCode whenever you override method equals.

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AssertionsAssertions

Verification in JUnit by calling assert which is inherited from TestCase. – Assert triggers a failure that is logged by JUnit when

the argument isn't true. – Since assertions for equality are very common,

TestCase defines an assertEquals convenience method. Logs the printed value of the two objects if they differ.

– Shows why a test failed in a JUnit test result report. Logged as a string representation created by toString.

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Test FixtureTest Fixture

public class MoneyTest extends TestCase {

private Money f12CHF;

private Money f14CHF;

protected void setUp() {

f12CHF= new Money(12, "CHF");

f14CHF= new Money(14, "CHF");

}

}

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Tests RefactoredTests Refactoredpublic void testEquals() {

assert(!f12CHF.equals(null));

assertEquals(f12CHF, f12CHF);

assertEquals(f12CHF, new Money(12, "CHF"));

assert(!f12CHF.equals(f14CHF));

}

public void testSimpleAdd() {

Money expected= new Money(26, "CHF");

Money result= f12CHF.add(f14CHF);

assert(expected.equals(result));

}

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Running of TestsRunning of Tests

Two additional steps are needed to run the two test cases:1. define how to run an individual test case,

2. define how to run a test suite.

JUnit supports two ways of running single tests:– static.– dynamic.

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Test Case: StaticTest Case: Static Overrides the runTest method inherited from TestCase and

call the desired test case. – Convenient way: anonymous inner class.– Note: each test must be given a name to identify it if it fails.

TestCase test = new MoneyTest("simple add") {

public void runTest() {

testSimpleAdd();

}

};

– A template method in the super-class will make sure runTest is executed when the time comes.

Dynamic: TestCase test = new MoneyTest("testSimpleAdd");

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Test Suite: DynamicTest Suite: Dynamic

Illustration of the creation of a test suite with the dynamic way to run a test:– You only pass the class with the tests to a TestSuite

and it extracts the test methods automatically.

public static Test suite() {return new TestSuite(MoneyTest.class);

}

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Test Suite: StaticTest Suite: Staticpublic static Test suite() { TestSuite suite= new TestSuite(); suite.addTest(new MoneyTest("money equals"){ protected void runTest() {

testEquals(); }

} ); suite.addTest(new MoneyTest("simple add") { protected void runTest() {

testSimpleAdd(); }

} ); return suite; }

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JUnit ReviewJUnit Review (1) (1)

In general: development will go much smoother writing tests a little at a time when developing.

When coding the imagination of how the code will work. Capture the thoughts in a test.

Test code is just like model code in working best if it is factored well.

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JUnit ReviewJUnit Review (2) (2)

Keeping old tests running is just as important as making new ones run.

The ideal is to always run all of your tests. When you are struck by an idea, defer thinking

about the implementation. First write the test. Then run it. Then work on the implementation.

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Testing PracticesTesting Practices (1) (1)

Martin Fowler: "Whenever you are tempted to type something into a print statement or a debugger expression, write it as a test instead.”

Only a fraction of the tests are actually useful. – Write tests that fail even though they should work,

or tests that succeed even though they should fail. – Think of it is in cost/benefit terms. You want tests

that pay you back with information.

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Receive a reasonable return on your testing investment: – During Development. – During Debugging.

Caution:– Once you get them running, make sure they stay running.

Ideally, run every test in the suite every time you change a method. Practically, the suite will soon grow too large to run all the time.

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Try to optimise your set-up code so you can run all the tests.

Or, – create special suites that contain all the tests that might

possibly be affected by your current development. – run the suite every time you compile. – make sure you run every test at least once a day: overnight,

during lunch, during one of those long meetings….

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ReferencesReferences

Code Complete; Steve McConnell, Microsoft Press.

The Elements of Java Style; Allan Vermeulen, SIGS Reference Library, Cambridge

http://www.javareport.com/ http://www.catapult-technologies.com/whitepapers/jlog/ http://www.junit.org/

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