Data Structures

You will need the Java Development Kit, an editor to write Java code, and extensions to add helpful features. Install all of the following links, in this order.

You will also need to install Java 17. Visit this page, and select Java 17 and which Operating System you are on. Then download an installer for Java 17 and run it.

Visual Studio Code is a text editor we use in CS112 to write Java code, install it from here.

Once you install Java 17 and VSCode, you can type “java -version” in the terminal, which should show you the version installed. If you get an error, but did download AND run the JDK, try restarting VSCode.

You should also install the following VSCode extension packs for Java, either through your web browser or the “Extensions” tab in VSCode.

• Extension Pack for Java
• Project Manager for Java
• Debugger for Java
• Test Runner for Java

Terminal / Command line. The terminal is a text interface to interact with the computer, it is already part of VScode. It’s a program that takes in commands, which it passes on to the computer’s operating system to run.

From the command line, you can navigate through files and folders on your computer, just as you would with a file graphic navigation interface like Windows’ File Explorer or Mac Os’ Finder. Here is a list of commands.

Some Useful Commands Are:

• “pwd” aka Print Working Directory, which prints the file path of the folder which the terminal is currently in. While the terminal is inside a folder, it only has direct access to the files in that folder. To access files outside, you must either move the current working directory (next command) or specify the exact path.
• “cd” aka Change Directory, which changes the current working directory of the terminal.
  • Note: Typing “.” represents the current working directory. So if there your current working directory is in a folder called “Test”, and inside that Test folder there is another folder called “Inner”, then you can navigate to that Inner folder with “cd ./Inner” or just “cd Inner”.
  • Note: To back out of a folder, into the folder which contains it, use “..” (i.e. to reverse the example above and go from Inner back to Test, do “cd ..”)
• “ls” aka List, which lists all the files and folders in the current working directory.
• You can also compile and run java programs with arguments through the command line. See any specific programming assignment for more info.

These commands are useful, as you will need to be in the main project folder for assignments to compile and run via the terminal. The main project folder is the one which directly contains the “src” folder as well as input files.

• For assignments to run via the VSCode run button, you will also need to be in the main project folder. However, the terminal does not control the VSCode working directory (it only controls the terminals working directory). Instead, ensure you open the main project folder with File -> Open Folder.

Short videos on how to use basic command line commands:

• Linux/MacOS
• Windows.

Writing your first Java program. How to video on how to use VScode and the command line.

Read the OOP Review for a rundown on Object Oriented Java programming.

Try it! Open a New Folder in VSCode, and create a new Java file named “HelloWorld.java”. This should automatically create a “public class HelloWorld { }” class header. Inside the brackets, you can then create methods and class attributes.

Write a method with the header “public static void main(String[] args) { }”, this is referred to as the main method. This method’s code is what is actually ran when you run your java file directly, either through vscode or the command line.

• The Drivers from your programming assignments use main() to start the Display and test cases.

Then inside the body of your main method, write “System.out.println(“Hello World!”);

When saved, compiled, and ran, this should now print “Hello World!” to your Teminal.

How do I approach a programming assignment? We suggest the following steps to complete your programming assignments successfully:

1. Spend some time thinking about the problem. Remember that the computer is really stupid and requires very specific and incremental steps to solve a problem. Think about the inputs and outputs to your algorithm, as well as possible errors you may encounter. Use psedocode to write test algorithms
2. Think about how you can test your code as you write it. As you write methods and implement algorithms, you should be confirming that it functions as you expect. This helps you to narrow down the amount of areas which you have to debug later on. See the Debugging and Testing Page for more.
3. Unzip the files we provide, and start coding your algorithm into the appropriate file. A good practice is to compile your program often to catch syntax errors sooner rather than later and ending up with a huge number of errors. If your program has compiling errors, always fix the first one and compile again. Often fixing the first one will remove the remaining errors.
4. DO NOT IGNORE any red lines (errors) in VSCode. These will prevent your program from running. When you hover over these, they will tell you what the issue is. It is important to be able to understand these error messages and determine the cause, and fix them. Often, it is a very simple fix, or a misunderstanding of the code which causes them.
5. Once you compile successfully, run your test cases and evaluate your output.
6. Come to office hours for help, or ask questions on Piazza. Piazza’s link is on Canvas sidebar.
7. When fully satisfied with your results and test cases submit your assignment.
8. Read the Hints given by autolab, and try to determine the cause of any errors. Use more custom tests with edge cases to try and find tiny issues in your program.

How can I extract the .zip file associated with an assignment? All files related to an assignment are bundled together in a .zip file, which you will need to extract:

• Zip files on MacOS. Download the .zip file listed on the assignment page. In Finder, view the directory containing the downloaded .zip file. Some browsers will automatically unzip the .zip file and create a project folder — which will have the same name without the .zip extension — containing the individual files. (Some browsers may also delete the original .zip file.) Otherwise, if you see the .zip file but no project folder, double-click the .zip file to create the project folder. You will want to create the .java files in this project folder.
• Zip files on Windows. Download the .zip file listed on the assignment page. In File Explorer, view the directory containing the downloaded .zip file. Right-click on the .zip file and select Extract All…, which will ask you to choose the extraction location. This creates a new project folder — which will have the same name without the .zip extension — containing the individual files.. (Do not double click the .zip file—that browses the contents instead of extracting them.)