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BY MARKUS SPRUNCK
BY MARKUS SPRUNCK
This article focuses on preconditions which are directly part of the source code. It doesn't cover other approaches which use annotations and aspect oriented programming.
Motivation
Motivation
The use of preconditions, post-conditions and invariants is extremely helpful to develop maintainable code. Unfortunately, we find preconditions quite seldom in real world applications. In some cases you can read correct preconditions in JavaDoc comments.
Two disadvantages of JavaDoc comments are that: (i) they just get outdated in cases the implementation changes and (ii) most of the developers just don't read them or read them too late.
Example Code
Example Code
In the example code you may see four different ways to directly implement preconditions and the use of asserts (run the code with VM option -ea to enable asserts).
Find Code on GitHub
Find Code on GitHub
Dependencies
Dependencies
To compile the code (see link below) you will need the following libraries:
Summary
Summary
Usage of Plain Java Validation
Usage of Plain Java Validation
Description:
Check the needed condition and throw the appropriate exception
Advantage:
Works always without additional external libraries
Disadvantage:
Needs a lot of code.
Message string can not use parameters
Example:
Usage of Guava Preconditions
Usage of Guava Preconditions
Description:
The class Preconditions may throw:
IllegalArgumentException
NullPointerException
IllegalStateException
IndexOutOfBoundsException
Advantage:
Message string can use parameters
Works with GWT
Disadvantage:
footprint very large
Example:
Usage of Apache Commons Validate
Usage of Apache Commons Validate
Description:
The class Validate may throw:
NullPointerException
IllegalArgumentException
IndexOutOfBoundsException
Advantage:
Message string can use parameters
Disadvantage:
footprint larg
Example:
Usage of Spring Framework Assert
Usage of Spring Framework Assert
Description:
The class Validate may throw:
IllegalArgumentException
IllegalStateException
Advantage:
Automatically part of applications which use Spring framework
Disadvantage:
Message string can not use parameters
Just basic functionality
Example:
Usage of Plain Java Asserts
Usage of Plain Java Asserts
Description:
Don't use assertions to do work that your application requires for correct operation in business logic.
If the condition is false, the assert throws an AssertionError with just the message text.
Must be enabled during run time with VM option.
Advantage:
Good for checks during development and for documentation purposes
May be a source of errors if business logic is part of asserts.
Disadvantage:
An assertion failure will never throw an appropriate exceptions, everything is just an AssertionError.
Message string can not use parameters.
Example:
Expected Output
Expected Output
When you run the sample code something like this is the output:
Recommendations
Recommendations
Use Preconditions in your code, this is most of the time better than a lot of comments, but don't use asserts as preconditions.
But, I can't recommend assert to check preconditions, but you may mix asserts with the four other approaches.
Guava Preconditions and Apache Commons Validate class are the best choice. They have almost the same functionality, just take what is more convenient in your technology stack.
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