1. PA1 Discussion

2. Today Review Multithreading in Java Discuss Client-Server Architecture
Some Hints on PA1

3. Thread Concepts
A program may consist of many tasks that can run concurrently. A thread is the flow of execution of a task.

4. Thread Concepts
In Java, each task is an instance of the Runnable interface, also called a runnable object. A thread is essentially an object that facilitates the execution of a task.

5. Thread Concepts
When your program executes as an application, the Java interpreter starts a thread for main method. You can create additional threads to run concurrent tasks.
Task 1: print the letter “a” 50 times
Task 2: print the letter “b” 50 times
Task 3: print the integers 1 through 50
Example 1: TestThread1.java

6. Thread Concepts
Another way to create a multithreading program is to define a class that extends class Thread and implements the run() method.

7. Thread Concepts We will take this approach for PA1!
Another way to create a multithreading program is to define a class that extends class Thread and implements the run method.
Task 1: print letter “z” 50 times
Task 2: print integers 1 through 50
Example 2: TestThread2.java

8. Thread Synchronization
A shared resource may become corrupted if it is accessed simultaneously by multiple threads. To avoid race conditions, it is necessary to prevent more than one thread from simultaneously entering a certain part of the program.
The keyword synchronized: acquire a lock of an object or class first before executing a block of code or a method.
Example 3: TestThread3.java

9. Part I: Writing a Client-Server Application
#status I just woke up!
#statusPosted
User
User input: I just woke up!

10. Part II: Implementing a Broadcast Status Update Using Multi-threading
How does the server manage multiple clients?
How does each user broadcast messages?

11. Part III: Adding Friendship / Multicast Capability to the Social Media App
private final userThread[] threads;
ArrayList<String> friends = new ArrayList<String>();
ArrayList<String> friendrequests = new ArrayList<String>(); //keep track of sent friend requests