Read the Javadoc for the WordAnalyzer class and its methods, but not the actual source.
You can open the Javadoc from IntelliJ by opening the javadoc folder,
right-clicking on index.html, and choosing "Open in Browser" from the context menu.
Assuming the code works as described in the Javadoc, if we initialized a
WordAnalyzer with the string "toothless", firstRepeatedCharacter()
would return 'o'.
Read this print debugging example.
Run the main method in WordAnalyzerTest from IntelliJ.
The class is in the tst directory (parallel to src,
in the root of the snippets package repository). Find the
main method and click the little green play button in the margin. Select 'Run WordAnalyzerTest.main()'.
From the results, you can see that the WordAnalyzer doesn't work as expected, and the tests fail.
Add some print statements to WordAnalyzer to figure out why
firstRepeatedCharacter() is not behaving as expected. Don't make any changes
to WordAnalyzerTest. When you understand the problem, fix it.
Do not fix any other methods.
Once firstRepeatedCharacter() is fixed, the print statements are no longer
helpful. In fact, they're cluttering the code and the output, causing readability
problems. Remove them.
There's more to fix here; we'll explore another debugging method before we push any code.
Watch Debugging in IntelliJ from 00:20 to 14:04. Since your icons may look a little different, pay attention to the command names, like "step over", so you can find the appropriate icons in your version of IntelliJ.
Vocabulary alert! The presenter uses some terms you may not know yet. These aren't in the learning objectives, so you don't need to memorize them:
logical bug: An error in code that causes incorrect results for valid expected inputs. Code with logical bugs compiles properly, but works improperly.flow of execution: The order that code statements are executed. This is also called "flow control". In code, statements likeifcan change the flow of execution. The debugger allows you to observe and control the flow by specifying where to interrupt and when to continue.
The presenter runs his program multiple times, and has to enter the same values each time to duplicate the error. This could be easier if they had written a test, and we'll learn an easy way to run tests in the Unit Testing lesson. If your debugging process does not include a way to make reproducing the bug easier, consider adding one.
Next, let's use the "step over", "step into", and "step out" to find another bug.
Run the WordAnalyzerTest again. Earlier, you fixed
firstRepeatedCharacter(), but now the test shows that
firstMultipleCharacter() is broken. (You didn't cause this error; the
test is just progressing farther now.)
Let's debug this problem without using any print statements at all. When you feel a print statement would be useful, use the debugger's variable panel. You could even set a watch.
Set a breakpoint that will help you observe the behavior of
firstMultipleCharacter() and start the debugger. Use step over,
step into, and step out to observe the behavior of
firstMultipleCharacter() and find(). Use the variable display in the
debugger panel to observe the state of the program.
Fix the program until the firstMultipleCharacter() tests pass.
Run the WordAnalyzerTest again. The countRepeatedCharacters() tests
have some failures.
You've already explored debugging with print statements and debugging with the
interactive debugger. Apply your debugging process with either method to find
and fix the problems in the program until the WordAnalyzerTest succeeds.