Add understanding Java workshop

understanding-java/.gitignore

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+/DnsResolver.class

understanding-java/DnsResolver.java

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+import java.net.InetAddress;
+import java.net.UnknownHostException;
+
+class DnsResolver {
+    public static void main(String[] args) {
+        if (args.length != 1) {
+            System.err.printf("Expected exactly one argument, but got %d%n", args.length);
+            System.exit(1);
+        }
+        String host = args[0];
+
+        String[] parts = host.split("\\.");
+        System.out.printf("The top-level domain of the host %s is %s%n", host, parts[parts.length - 1]);
+
+        try {
+            InetAddress[] ipAddresses = InetAddress.getAllByName(host);
+            if (ipAddresses.length == 0) {
+                System.out.printf("The host %s did not resolve to any IP addresses%n", host);
+            } else {
+                String pluralSuffix = ipAddresses.length == 1 ? "" : "es";
+                System.out.printf("The host %s resolved to the following IP address%s:%n", host, pluralSuffix);
+            }
+            for (InetAddress ipAddress : ipAddresses) {
+                System.out.println(ipAddress.getHostAddress());
+            }
+        } catch (UnknownHostException e) {
+            System.err.printf("Failed to resolve %s: %s%n", host, e.getMessage());
+            System.exit(1);
+        }
+    }
+}

understanding-java/README.md

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+# Understanding Java
+
+No one (neither trainees nor volunteers) involved in this workshop needs to know Java.
+
+The goal of this workshop is to work with code _even though we don't know the language_.
+
+Trainees should be familiar with any programming language (e.g. JavaScript or Python), and should be comfortable searching for and reading documentation.
+
+## Learning objectives
+
+```objectives
+- [ ] Make sense of code in a language you don't know.
+- [ ] Identify similarities and differences between programming languages.
+- [ ] Use documentation, debugging, and search techniques to fix a bug in a program in a language you don't know.
+- [ ] Use documentation, debugging, and search techniques to extend a program in a language you don't know.
+```
+
+## Introduction
+
+There are a lot of things in common across different programming languages.
+
+Even if you don't know Java, knowing other languages gives you a basis for making sense of it.
+
+All of your existing documentation/research/Googling skills will help you!
+
+Get into groups of no more than 6.
+
+## Understanding code (10 minutes)
+
+Here is some Java code:
+
+```java
+class DnsResolver {
+    public static void main(String[] args) {
+        if (args.length != 1) {
+            System.err.printf("Expected exactly one argument, but got %d%n", args.length);
+            System.exit(1);
+        }
+        String host = args[0];
+
+        String[] parts = host.split(".");
+        System.out.printf("The top-level domain of the host %s is %s%n", host, parts[parts.length - 1]);
+    }
+}
+```
+
+Set a timer for 10 minutes.
+
+Take 10 minutes to play computer with this code on your own. Read through it line-by-line and work out what you think each line does.
+
+Identify what things you don't know, or haven't seen before in another language. Try to work out what they are. First make a guess, and if you're not confident, do some research.
+
+Identify what things you _have_ seen in another language, and what the equivalent code in that language may be.
+
+## Discuss new is similar and what is new (15 minutes)
+
+Popcorn around your group discussing what things in this code are _similar_ to what you've seen in other languages, and what things are different.
+
+Discuss the things that are different:
+* What trade-offs do you think they bring?
+* What extra value do they give compared to how things would look in other languages?
+* What draw-backs do they have?
+
+## Debugging code (15 minutes)
+
+Set a timer for 15 minutes.
+
+On your own, predict what you expect this code to do and print.
+
+Save the above Java code to a file named `DnsResolver.java`. From the same directory as the file, run the following command:
+
+```bash
+javac DnsResolver.java && java DnsResolver google.com
+```
+
+This does two things - it _compiles_ the `DnsResolver.java` file into a file called `DnsResolver.class`, and then it runs that file with the argument `google.com`.
+
+If you run this command, you may see different results than what you expect. Compare this with your prediction.
+
+In your group, try to debug and fix this problem. Share theories about what's happening, suggest how you could get more information, and work together.
+
+## Extending code (50 minutes)
+
+Add additional code to the existing code to satisfy an additional requirement:
+
+Resolve the DNS hostname passed as the program's command line argument, and print out the IP addresses it resolves to.
+
+If you run your finished program, it should behave similar to below (but the actual values may be different):
+
+```console
+% java DnsResolver codeyourfuture.io
+The top-level domain of the host codeyourfuture.io is io
+The host codeyourfuture.io resolved to the following IP address:
+54.72.81.102
+
+% java DnsResolver google.com
+The top-level domain of the host google.com is com
+The host google.com resolved to the following IP addresses:
+142.250.179.238
+2a00:1450:4009:81d:0:0:0:200e
+```
+
+You can work on your own or in groups to do this.
+
+## Sample implementation
+
+A sample complete implementation of this exercise can be found in https://github.com/CodeYourFuture/CYF-Workshops/blob/main/understanding-java/DnsResolver.java but we recommend you try to completely solve the exercises yourself rather than looking at the sample implementation.