Lab 05 - Logical Garden

In this lab, you will work with a small gardening program to practice using logical operators and conditionals.

Step 1: Compiling and Initial Runtime Errors

Run the main method in GardenHelper.java. Does your code compile? If so, great. Exit the program. Make sure that so far, your program is functioning as normal. If you have any trouble exiting your program, check your code, specifically the go() method in GardenHelper.java to see what might be causing this issue. (Hint: The prompts on the screen are correct, those should not be changed.)

Step 2: Self-Explanation

Take a look at GardenHelper.java and its methods addRow() and addPlant(). We have provided addPlant() for you, but it is important to determine what it is doing so you can implement addRow() properly. Use the code and the javadoc to write a brief explanation of what addPlant() is doing and brainstorm what else you need to do for addRow().

Step 3: Implementation

Implement addRow() in the code now that you have written out how it should work.

Step 4: Testing

We have provided two test cases for you in GardenHelper.java's main method. For testing specific methods, run from GardenHelper.java's main and only the tests you have uncommented will run. Running from GardenMain.java's main will run the program in its entirety. Add more test cases to GardenHelper.java's main make sure addRow() works properly before running the whole program too much. Once you test the methods individually, make sure to test the program in its entirety. Run your program from the GardenHelper.java main, and run through the program a few times, trying different plants and row conditions.

Step 5: Turning In

1. Turn in your program files to Zybooks
2. Show your self-explanation, pseudocode, and tests to your TA (in-person). Online students do not have the option to submit their self-explanations. They are still highly recommended to complete as they better help your understanding of the code.

Extra Practice (Optional)

You may have noticed in your testing that there are some things we just assume to be true. For example, that the user will enter row 1-3 and not some other number. For some extra practice, make a list of the methods that bugs could possibly be introduced, and make some test cases that break the code.

Additional Background Information

Something that will be very useful for this lab is understanding how to call methods from other methods. Each method has a return type, whether it be a simple getter or a complex method. We can use our knowledge of the return type as well as the functionality of a method to chain multiple methods together.

For example, we have used the .equals() method before.

str = "apples";
if(str.equals("oranges")){
    //do something
}

Now, instead of calling just one method, the .equals() method, we can call the equals() method and the getName() method. (This is assuming we have a Fruit object that has a name variable and is associated with getName() method)

Fruit fruit1 = new Fruit("orange");
if(fruit1.getName().equals("orange")){
    //do something
}

Or even more complex:

Fruit fruit1 = new Fruit("orange");
Fruit fruit2 = new Fruit("banana");
if(fruit1.getName().equals(fruit2.getName())){
    //do something
}

What's happening here is kind of like a relay race. The methods are executed one at a time, and the return value handed back to computer to use in the next method.

A more complete breakdown of how the computer goes through the if(fruit1.getName().equals(fruit2.getName())) example:

1. Evaluate the if statement, which is the result of the .equals() statement. We need to know what we are comparing first, however.
2. Look at the first part of the .equals(). Execute fruit1.getName(), which returns "orange". A simplified version would look like: if("orange".equals(fruit2.getName()))
3. Look at the second part of the .equals(). Execute fruit2.getName(), which returns "banana". A simplified version would look like: if("orange".equals("banana"))
4. Finish evaluating the if statement, which is false.

Even though the initial if statement looks long and complicated, if you are careful about what methods you are calling and when, condensing your code like this is much better practice and will reduce the likelihood of bugs since you are directly calling your methods.

To check if multiple conditions are true, logical operators and nested if-statements can be used. Each has their own benefits.

Logical Operator Examples:

//if fruit1's name is orange OR banana, do something
if(fruit1.getName().equals("orange") || fruit1.getName().equals("banana")){
    //do something
}

int a = 1;
int b = 2;
int c = 5;
//if a + b is 3 AND a OR b is less than c, do something
if( ((a + b) == 3) && ((a < c) || (b < c)) ){
    //do something
}

These if statements can get a bit lengthy, but are useful when there are multiple conditions that must be met for a particular outcome to happen.

Nested if Statement Example:

if(plant1.isVegetable()){
    if(plant1.isBroccoli()){
        //ew! don't eat it
    }
    else {
        //eat it
    }
}
else{
    //don't eat it
}

While this could have been implemented with logical operators, some situations are more useful with logical operators and some with nested if statements.

The final thing to mention for this lab is the dreaded null pointer exception. This "Billion Dollar Mistake" is important to consider if you get NullPointerException errors. Sometimes, like if you are searching for an object, if the computer doesn't find the object it will return null. If that return value is being called on by another method, there will be a null pointer exception.

For example:

int id = searchBook("Hamlet").getId();
//if searchBook("Hamlet") returns null, 
//null.getId() will result in a NullPointerException

To fix this, you can add a [variable] != null condition.

For example:

if(searchBook("Hamlet") != null){
  int id = searchBook("Hamlet").getId();
}

or

if(searchBook("Hamlet") != null && searchBook("Hamlet").getId() == 5){
    //do something
}