How do I insert a precondition in a java class method or constructor?

java assert design-by-contract preconditions
Jay Rohrssen picture Jay Rohrssen · Nov 18, 2012 · Viewed 13.5k times · Source

This is for a java class I'm taking. The book mentions preconditions and postconditions but doesn't give any examples how to code them. It goes on to talk about asserts, I have that down, but the assignment I'm doing specifically states to insert preconditions and test the preconditions with asserts.

Any help would be great.

Answer

paulsm4 picture paulsm4 · Nov 18, 2012

Languages like Eiffel support "preconditions" and "postconditions" as a basic part of the language.

One can make a compelling argument that the whole purpose of an "object constructor" is precisely to establish "the class invariant".

But with Java (as with just about every other post-C++ object oriented language), you pretty much have to fake it.

Here's an excellent tech note on leveraging Java "assert":

Related questions

How do you assert that a certain exception is thrown in JUnit 4 tests?

How can I use JUnit4 idiomatically to test that some code throws an exception? While I can certainly do something like this: @Test public void testFooThrowsIndexOutOfBoundsException() { boolean thrown = false; try { foo.doStuff(); } catch (IndexOutOfBoundsException e) { thrown = true; } assertTrue(thrown); } I …

Read More
Java/ JUnit - AssertTrue vs AssertFalse

I'm pretty new to Java and am following the Eclipse Total Beginner's Tutorials. They are all very helpful, but in Lesson 12, he uses assertTrue for one test case and assertFalse for another. Here's the code: // Check the book out to …

Read More
How to do a JUnit assert on a message in a logger

I have some code-under-test that calls on a Java logger to report its status. In the JUnit test code, I would like to verify that the correct log entry was made in this logger. Something along the following lines: methodUnderTest(…

Read More