Equivalent If Statements

Sometimes there are many different ways to write boolean expression to get the result that you want. If you attempt to write a solution and it doesn't look exactly the way we present it in these tutorials, that doesn't mean that you are wrong necessarily. This is also true if you are working with another programmer. In this section, we will look at how to write statements that all do the same thing in a variety of ways.

Your Turn

Let's try it in the Java Playground.

In this example, we want to increase the grade level of a student, if they passed and are not a senior. If they passed and are a senior we want to print, "Congratulations!".
Recall that ++ updates the value of the variable to the current value plus 1.
Predict the output of the code.
Run the code and determine if your prediction is correct.
Adjust the value of passed to false. Predict the output. Run the code and determine if your prediction is correct.
Adjust the values of passed to true and gradeLevel to 12. Predict the output. Run the code and detemine if your prediction is correct.
Adjust the value of passed to false. Predict the output. Run the code and determine if your prediction is correct.

Alternate Solution

The following is an alternate solution.
Predict the output of the code.
Run the code and determine if your prediction is correct.
Adjust the value of passed to false. Predict the output. Run the code and determine if your prediction is correct.
Adjust the values of passed to true and gradeLevel to 12. Predict the output. Run the code and detemine if your prediction is correct.
Adjust the value of passed to false. Predict the output. Run the code and determine if your prediction is correct.

Not Equivalent Solution

The following solution is not equivalent.
Predict the output of the code.
Run the code and determine if your prediction is correct.
Adjust the value of passed to false. Predict the output. Run the code and determine if your prediction is correct.
Adjust the values of passed to true and gradeLevel to 12. Predict the output. Run the code and detemine if your prediction is correct.
Adjust the value of passed to false. Predict the output. Run the code and determine if your prediction is correct.
Update the code to initialize gradeLevel to 11. The first boolean condition will evaluate to true and gradeLevel will have the value 12. Then the second boolean condition will also evaluate to true and the program will print "Congratulations!".

Testing Your Code

As you can see, this last solution looks good on the surface but does not function the same way in the case of gradeLevel having an initial value of 11. Writing out the expected behavior of your program code before you start can be helpful when you test and debug your code later. For the code provided, here are some test cases that would help us identify whether the program code is function as we expect it to or not. Take a few minutes to run each test case on the original code, alternate solution, and the not equivalent alternate solution to see which case causes the not equivalent solution to fail.

Test Case	Expected Result	Description
`gradeLevel = 9` `passed = true`	prints: `10`	The value of `gradeLevel` will be increased to `10` and `Congratulations!` is not printed.
`gradeLevel = 12` `passed = true`	prints: `Congratulations! 12`	The value of `gradeLevel` will stay `12` and `Congratulations!` will be printed.
`gradeLevel = 11` `passed = true`	prints: `11`	The value of `gradeLevel` will be increased to `12` and `Congratulations!` is not printed.
`gradeLevel = 9` `passed = false`	prints: `10`	The value of `gradeLevel` will stay the same and `Congratulations!` is not printed.
`gradeLevel = 12` `passed = false`	prints: `12`	The value of `gradeLevel` will stay the same and `Congratulations!` is not printed.
`gradeLevel = 11` `passed = false`	prints: `11`	The value of `gradeLevel` will stay the same and `Congratulations!` is not printed.

Resources

Next Learn Tutorial

Learn: Using the Conditional Operator