CS 49J - Lab 1

Cay S. Horstmann

Lab Rules

• Work with a buddy (the person sitting next to you)
• Post lab report to Canvas
  • Plain text
  • Need not be literary masterpiece
  • Both you and your buddy submit, but you can submit the same if you like
• Share your results with the class
  • Show and tell

Step 1. Housekeeping

1. Did you sign up to Piazza?
2. Did you upload your picture to Canvas?

Step 2. Eclipse

1. Open Eclipse. Make a new Java project lab1. Make a new class Hello. Be sure it is in the default package. Clear out the Package: field. Then paste in this code:

   public class Hello
   {
      public static void main(String[] args)
      {
         System.out.println("Hello \uD83D\uDE3B!");
      }
   }
   

   Run the program. What happens?
2. Change main to Main. Compile and run. What happens?
3. Change it back. Change System.out to System.uot. What happens?
4. Change it back. Move the cursor after the second ", i.e. before the );. Type a period and to. If nothing happens, hit Ctrl+Space. (Might be Option+Space on the Mac.) What happens?
5. Select toUpperCase() and run the program again. What happens?

Step 3. Book Code

1. Unzip the book code somewhere on your computer. (Link on course web page...)
2. In Eclipse, make a new project. But this time, uncheck the box Use default location. Then browse to corejava/v1ch02/ImageViewer whereever you unzipped the book code. Note that the project name is set to ImageViewer. Click Finish.
3. Run the app. What does it do?
4. Glance at the code. In your opinion, is that a lot of code for writing such an app, or not very much code at all?

Step 4. The Command Line

1. Open a terminal window. Type

   javac -version

   What happens? (If you get an error message and don't know how to fix it, ask for help.)
2. Change to the corejava/v1ch02/Welcome directory in the terminal.
3. Run

   javac Welcome.java
   java Welcome

   What happens?
4. What happens when you run

   javac Welcome

   ? Why?
5. What happens when you run

   java Welcome.java

   Why?

Step 5. CodeCheck

• In homework 1A, you solved a problem in C++/C/Python. Now you'll do it in Java. Go to this CodeCheck problem. Some parts are filled in since haven't yet learned how to do functions and loops in Java. Look at your solution in C++/C/Python, and turn it into a Java solution that fits into the outline. What did you get?
• What happened when you submitted it?
• What is in the zip file that you get when you click on the Download link?

Step 6. CodeCheck and Eclipse

• For a very simple problem, you can type your work into the CodeCheck text area. But then you lose all the goodness of Eclipse, such as autocompletion. Also, it's easy to lose all your work. It's better to work in Eclipse and only paste your answer into CodeCheck when you are happy with it.
  Make a project hw1a in Eclipse. Add two classes, Arrays and Tester. Copy/paste from CodeCheck. The Arrays class should have your solution from the preceding page. What happens when you run it?
• As you can see, you don't get green and red lines. Eclipse knows nothing about the Expected: syntax. You'll need to compare the output yourself. Once you are satisfied, check it with CodeCheck.

Step 7. CodeCheck and Eclipse Part 2

• Now look at the CodeCheck for the Java version of the second problem in homework 1. Note that there isn't a Tester. Instead, the test cases are invisible.
  To see the test cases, change the body of the splice method to

  return "";

  Now run CodeCheck. What happens?
• In Eclipse, make a project hw1b and make classes Strings and Tester. In the Tester class, do something similar to the Tester class in the the first assignment. That is, print the values that you actually get when calling the method with the test arguments. Then print "Expected: HWeolrllod" for the first test case, and similarly for the others.
• Now go back to CodeCheck for the Java version and paste the skeleton code for the Java solution into your Strings class. It tells you enough about strings that you should be able to translate your C++/C/Python solution. Ask for help if you can't. What is your Java solution?
• What happens when you run the Tester in Eclipse?
• What happens when you run your solution in CodeCheck?

Step 8 (Optional). The Most Frequent Element

• Remember what we talked about on Monday? How do you find the most frequent element in an array? Let's make a very long array.

  int[] values = new int[1000000];
  for (int i = 0; i < values.length; i++) values[i] = (int) (values.length *Math.sin(i));
  

  Let's sort it:

  java.util.Arrays.sort(values);
  

  Let's see the first 10000 elements:

  for (int i = 0; i < 10000; i++) System.out.println(values[i]);

  Put all this into a class MostFrequent and run it. What do you get?
• Ok, we still don't know what the most frequent value is. Put in the code that we discussed on Monday. What is your code?
• What is the most frequent value?
• Is it unique? Or are there multiple values of that maximum frequency? How did you find out?