CS 49J - Lab 2

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. A Java REPL

1. JDK 9 has jshell, a “read-eval-print-loop”, that you saw in the videos. If you have Java 9 installed, you execute it by running

   path to JDK/bin/jshell

   We'll do that eventually, but for today we'll use the online version. Type in

   Integer.toBinaryString(5)

   and hit Enter. What do you get?
2. What do you get for

   Integer.toHexString(60)
   

   Why? (Hint: A is 10, B is 11, C is 12.)
3. What do you get for

   Integer.valueOf("101", 2)

Step 2. A Hex Viewer

1. Open Eclipse. Make a new Java project lab2. Make a new class HexViewer. Remember—be sure it is in the default package. Clear out the Package: field. Then paste this code.
   Also save this file to your Downloads directory. Depending on your browser and OS, you may need to right-click and select Save Link As or some such thing. Run the program. When the file dialog pops up, pick hello.txt from the Downloads directory. What happens?
2. This file uses the UTF-8 encoding, which is probably the most common encoding for Unicode in files. In UTF-8, each Unicode code point is encoded as a sequence of 1 - 4 bytes. In this file, all code points use one byte. What is the UTF-8 encoding in hex for the letter H? The letters e and l? The space? The exclamation mark?
3. What is the significance of the 0A at the end?

Step 3. More UTF-8 Encodings

1. This file contains the message

   Hello, San José!

   In UTF-8, the é is encoded as two bytes. What are they? Use the HexViewer and the hello2.txt file to find out. Be careful to use this exact file. Or, if you make your own file, be sure to save in UTF-8. (While the vast majority of computing devices defaults to UTF-8 for file encoding, both Windows and Mac OS still cling to archaic coding system defaults.)
2. Look up this webpage. Where do you find the UTF-8 encoding for é?
3. This file contains the message

   Hello, Java™!

   What is the UTF-8 encoding of the ™ symbol?
4. This file contains the message

   Hello 😻

   What is the UTF-8 encoding of the 😻 symbol?

Step 4. Running from the Command Line

1. A disadvantage of running a program from Eclipse is that you don't have an obvious place in the file system from where your program runs. If you need to navigate to another directory many times, that's not productive. This is where the command line comes in. Save the HexViewer source in the download directory.
2. Open a terminal window. Change to the download directory (cd Downloads). Type

   ls hello*.txt

   or, on Windows,

   dir hello*.txt

   What do you get? Then type

   ls *.java

   or, on Windows,

   dir *.java

   What do you get?
3. If you saw the various hello text files and HexViewer.java, then keep going. If not, ask for help.
4. Compile HexViewer from the command line. How do you do that?
5. Now run

   java HexViewer hello1.txt

   What happens?
6. How do you inspect hello2.txt? (Hint: Hit the ↑ key)
7. Is this better than using a file dialog? If so, why?

Step 5. Strings and UTF-16

1. Add this class to your lab2 project. Compile and run, and type in the input Hello. What happens?
2. What you are seeing are the UTF-16 encodings of the characters in the string. What is the UTF-16 code for H? For e? for l?
3. How are they related to the UTF-8 encoding?

Step 6. More UTF-16

1. We'd like to try the same thing with San José to figure out what happens with the é. But how is that going to work? Even if you know how to type an é on your computer, how do you know what character encoding is used in your console? To have complete control over this, we'll again read from a file. (As Vladimir Lenin said, “Trust is good. Control is better.”)
   Do what you did before. Download into your Downloads directory. Open a terminal window and use the cd command to change to that directory. Run

   javac StringPrinter.java
   java StringPrinter hello2.txt

   What happens? (If you get an error message, ask for help.)
2. What is the UTF-16 encoding for é?
3. What is the UTF-16 encoding for ™? How did you find out?
4. Running the same kind of experiment, what is the UTF-16 encoding for the smiling cat with heart-shaped eyes? What's different about it?

Step 7 (Optional) 🍹

1. Look at this page to find the Unicode code point for our smiling cat. What is it?
2. Ok, so how do we get from there to "\uD83D\uDE3B"? This page tells how to do it:
   • Subtract 0x10000.
   • Turn into binary strings. (See Step 1.)
   • Take the top and bottom ten digits, using substring. (You may not actually have twenty digits. Deal with that somehow.)
   • Turn each back into int. (See Step 1.)
   • Add 0xD800 to the first, 0xDC00 to the second.
   Write a Java program that carries out these steps and prints the two UTF-16 code units in hex.
3. Now make your program work for any code point ≥ U+10000. Read in the code point as a string U+1.... and do your thing. What do you get for U+1F379?
4. Even more extra time? Then tackle UTF-8.