4. Code Standards
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/CodeConvTO
C.doc.html.
4
5. Code Standards
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.
5
6. Code Standards
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.
6
7. Code Standards
Do it right the first time !
Your professionalism is expressed by
applying code standards !
Document any deviations!
7
8. Formatting
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.
8
9. 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
9
10. 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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11. Naming
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.
11
12. Naming
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.
12
14. Parameters
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
14
15. Comments; Why, when, where, 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.
15
17. Architecture; How to Avoid Spider-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.
17
18. Refactor to a New Architecture
::EcBpStreamShipper ::EcBpStreamFlare ::EcBpStreamFluid ::EcDpWellStream
::EcBpStream
::EcDpDerivedStream ::comp_analysis
::Theoretical ::EcDpStream ::EcDpWellReservoir ::EcDpStreamFluid ::calc_stream
18
19. Information 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.
19
20. Binding
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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21. Java Exceptions
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.
21
22. Java Exceptions
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.
22
23. Code Defensively
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.
23
24. Code Defensively
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.).
24
25. Summary
Remember your code should be
understandable.
Maintenance is often up to 70% of a total
project cost.
Use quality control.
25
27. Debugging
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
27
28. Application Logging: What 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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30. Logging Granularity
The greater the granularity, the deeper the
level of detail.
Agreed and documented set of event
categories determine the granularity to
log those events.
Separate logs for e.g.
– thread pool.
– SQL processor.
30
31. Logging 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.
31
32. Configuring the Logs
Configuration from a properties file.
LogFileExtension = log
LogFilePath = c:temp
LoggingLevel = 2
LoggingMechanism = log.StandardErrLoggingMechanism
LogFieldSeparator = |
32
33. Configuring the Logs
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.
33
34. Configuring the Logs
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);
34
35. Configuring the Logs
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.
35
36. Reading the Logs
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.
36
37. Reading the Logs
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.
37
39. Testing
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.
39
40. JUnit
Automatic testing framework.
– Acceptance tests.
– Integration test.
– Unit test.
Reports the number of defects graphically.
May create many tests for each method.
40
41. JUnit 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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42. Example: Money
class 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;
}
}
42
43. JUnit
JUnit defines how to structure your test
cases and provides the tools to run them.
You implement a test in a subclass of
TestCase.
43
45. Junit
Define 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.
45
46. Example: MoneyTest
public class MoneyTest extends TestCase {
//…
public void testSimpleAdd() {
Money m12JPY= new Money(12, “JPY"); // (1)
Money m14JPY= new Money(14, “JPY");
Money expected= new Money(26, “JPY");
Money result= m12JPY.add(m14JPY); // (2)
assert(expected.equals(result)); // (3)
}
}
46
47. Developing Tests
public void testEquals() {
Money m12CHF= new Money(12, "CHF");
Money m14CHF= new Money(14, "CHF");
assert(!m12CHF.equals(null));
assertEquals(m12CHF, m12CHF);
assertEquals(m12CHF, new Money(12, "CHF")); // (1)
assert(!m12CHF.equals(m14CHF));
}
47
48. Developing Tests
public 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.
48
49. Assertions
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.
49
50. Test 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");
}
}
50
51. Tests Refactored
public 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));
}
51
52. Running 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.
52
53. Test 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");
53
54. Test 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);
}
54
55. Test Suite: Static
public 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;
}
55
56. JUnit Review
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.
56
57. JUnit Review
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.
57
58. Testing Practices
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.
58
59. Testing Practices
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.
59
60. Testing Practices
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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