Java Programming Best Practices Part V. Timothy Fagan Ishi Systems, Inc.

Transcription

1 Java Programming Best Practices Part V Timothy Fagan Ishi Systems, Inc.

2 Agenda Why do we need best practices? The Importance of Type-safety When and How to Summary

3 Why do we need best practices? Who will read your code? Compiler will tell you straight away if your code is invalid. You when you look at it again in three months. Some other luckless developer two years from now while you are on vacation - from your new job! What is worse, buggy code or incomprehensible code? Buggy but comprehensible code can be easily corrected. Correct but incomprehensible code is destined to become buggy as requirements change. Best practices help us to write maintainable code. Every week I see code like the examples included here - bad code is being written - do not contribute toward it.

4 The Importance of Type-safety private Object[] findmostcommon( List<String> alistofstrings) { int mostcommonoccurrences = 0; String mostcommonstring = null; for (String string : alistofstrings) { final int count = count(string, alistofstrings); if (count > mostcommonoccurrences ) { mostcommonoccurrences = count; mostcommonstring = string; return new Object[] { mostcommonstring, mostcommonoccurrences ;

5 The Importance of Type-safety final List<String> listofwords = Arrays.asList( new String[] { "bob", "mary", "max", "zoe", "mary", "frank" ); Object[] mostcommon = utility.findmostcommon(listofwords); String mostcommonword = (String) mostcommon[0]; int frequencyofmostcommonword = (Integer) mostcommon[1];

6 Introduce a type to return the result public static class Mode { public int count; public String string; public Mode(String astring, int acount) { count = acount; string = astring; private Mode findmode2(list<string> alistofstrings) { // as per previous version, then... return new Mode(mostCommonString, mostcommonoccurrences);

7 Introduce a type to return the result final List<String> listofwords = Arrays.asList( new String[] { "bob", "mary", "max", "zoe", "mary", "frank" ); Mode mostcommon = utility.findmostcommon2(listofwords); String mostcommonword = mostcommon.string; int frequencyofmostcommonword = mostcommon.count;

8 Annotations are not Edible { class Foo { String x;

9 Annotations are not Type-safe... yet! public void eat(object o) { if (o.getclass().isannotationpresent(edible.class)) { System.out.println("yum"); public void test() { Object object = new Foo(); // compiles and prints "yum" eat(object); String string = "don't eat me"; // compiles and prints nothing eat(string);

10 JSR 308: Annotations on Java Types public void Object o) { System.out.println("yum"); public void test() { Object object = new Foo(); // compiles and prints "yum" eat(object); String string = "don't eat me"; // using the correct pluggable type checker, // will not compile! eat(string);

11 Type-safety Relying upon compiler is never a substitute for good testing; however, failing to take advantage of the language and compiler's support for good design is inviting disaster. The compiler is your friend. Let is do as much boring heavy lifting as possible. Generics were added specifically because Java in general, and collections in particular, were prone to so many run-time errors. Down-casts are performed at run-time and are only discovered when the line of code is run. If the line of code is run infrequently, the error may not be detected for months. If the line of code is only run during error conditions, the error may eclipse the root cause!

12 Avoid private Future pollrequest(long delay, long frequency) { ThreadGroup threadgroup = new ThreadGroup(threadGroupName); scheduledexecutorservice = Executors.newScheduledThreadPool(threadPoolSize); final ScheduledFuture future = scheduledexecutorservice.schedulewithfixeddelay( new Runnable() public void run() { // do something, delay, frequency, TimeUnit.MINUTES); return future;

13 Limit it to the statement that requires it private Future pollrequest() { threadgroup = new ThreadGroup(threadGroupName); scheduledexecutorservice = Executors.newScheduledThreadPool(threadPoolSize); final Runnable command = new Runnable() public void run() { // do something final ScheduledFuture future = scheduledexecutorservice.schedulewithfixeddelay( command, initialdelay, frequency, TimeUnit.MINUTES); return future;

14 @SuppressWarnings as little as possible. The warnings that are provided are useful and typically help you write good code. Limit the will suppress warnings in all code within the scope of the annotated statement or block.

15 Summary Best practices are important. Type safety always Casting is mostly a sign of bad design Annotations are not safe... yet. Favour compile-time checks over runtime suppresses meaningful warnings Limit their use and limit their scope to maximize the quality of your code. They are only warnings, not errors, and sometimes they need to be ignored. Anyone can write complex code - few people can maintain it.