common java problems when developing with android

Software Engineering Large Practical

Common Java problems when coding forAndroid and advice for dealing with them

Stephen Gilmore

School of Informatics, University of Edinburgh

October 24th, 2012

Stephen Gilmore Software Engineering Large Practical

Java problems

For some, developing for the Android platform might provide theirfirst experience of working with a complex, modern Java API. Thismay test your knowledge of the Java programming language,especially with regard to features such as generics. The AndroidAPIs make use of generics throughout and so you will have toknow how to create and handle generic classes.


Raw types

Raw types are a backwards compatibility feature which allowednew generic Java code to use old non-generic libraries and to allownon-generic Java code to continue to compile and work on modernJava versions. Raw types are not needed when working with theAndroid API and your project should not contain them.


Common Java problems: raw types, 8 warnings

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Quick fix: a bad suggestion

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Check the constructor documentation

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Check the class documentation

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What type of array are we adapting?

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Type parameter added, 6 warnings

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Raw type parameters

Raw types need special treatment in method headers wheninstances of generic classes are being passed as parameters tomethods. A special syntax is used to specify when we do not knowthe type of the parameter to the generic class.


Raw type in method header, 5 warnings

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Consult the Java documentation

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Adapter doesn’t work here

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Adapter is an interface

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T is not a class

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Object: the goto class

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T extends Adapter doesn’t work

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“?” — the wild card parameter, 3 warnings

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“Quick fix” would have worked here

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Same result

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Working with the Java compiler

The Java compiler used Eclipse allows you to tune the level ofchecking which your program receives during compilation. Thischecking (“static analysis”) evaluates the correctness of yourprogram without executing it.

The default settings do not apply particularly strict checking. Werecommend tightening the default settings to detect errors in yourJava code which you may otherwise miss.


Setting Java compiler preferences

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Changing defaults

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Potential programming problems

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Tighter checking

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Bug found

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Remembering and forgetting while developing

Leaving an empty block is a classic “I must remember to do thatlater” error. By turning on stricter checking with the staticanalysis tools in the Java compiler we get automatic reminders inthe form of Java problems. These will persist in our project untilwe do go back and write the remaining code block.


Logging

As we have seen, the Android emulator occupies all of the screenreal estate of our virtual device, in order to allow us to test apps asthey will be used in practice. If we want to log informationalmessages for our own purposes then we should use the Androidlogging API.


Don’t forget to add logging . . .

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