---
tags: Setup-Summer21
---

# Lecture 4 Setup/Prep

In lecture 4, we will learn
- how to share helper functions and common fields across classes

We will continue building on the `Dillo`, `Boa`, and `Zoo` example from lecture 3. Download the [starter zip file for `lec04`](https://cs18-summer-2021.github.io/static/classes/4/lec04.zip). You can unzip this into your lectures project's `src` directory within IntelliJ.

Remember to use `Right-Click-on-lec03 -> Mark Directory As -> Excluded` to hide your `lec03` directory while we work on `lec04`.

## Prep
Last class, we saw the idea of an *interface* as the way to create a new type name in Java.

We also began to look at how to define a method (`isNormalSize`) that could work on either `Dillo` or `Boa` objects. At the very end of class, we put a version of that method in each of the two classes, and added it to the interface. This code is in the starter zip.

In lecture 4, we will:
- work through why we list method names in interfaces
- see how to handle code that is repeated across classes

In lecture 4, we'll build on that idea to better understand Java types, and add a helper function that should work with both `Dillo` and `Boa`.

We will work towards getting a well-designed Java program that supports the following `healthCheck` method in the `Zoo` class:

public class Zoo {
    IAnimal animal1;
    IAnimal animal2;

    public Zoo(IAnimal ani1, IAnimal ani2) {
        this.animal1 = ani1;
        this.animal2 = ani2;
    }

    /**
     Checks whether all animals in the zoo are normal size
     @return string indicating whether check passed or failed
     **/
    public String healthCheck() {
        if (animal1.isNormalSize() && animal2.isNormalSize()) {
            return "Passed";
        }
        else {
            return "Failed";
        }
    }
}

Things to prepare:

- Download the starter code (if relevant)
- Look at the `healthCheck` tests in the `AnimalTest` class: see if you can figure out how Java runs this function by tracking references to objects in memory
- List any questions that you have about the starter code