CONCURRENCY (Java)

🧠 CONCURRENCY (Java) – MINI STUDY GUIDE

🔹 1. What is Concurrency?

Definition (simple lang):
Concurrency means multiple tasks running at the same time.

👉 Think of it like this:

• Nagla-laptop ka 💻 habang naka-play music 🎧

• Or nagdo-download habang nagba-browse

💡 This part is important kasi ito ‘yung foundation ng topic.

Key Ideas:

• A multithreaded program has multiple parts running at once

• Helps improve efficiency (di sayang oras habang naghihintay)

📌 From your handout (page 1):
Concurrency allows tasks waiting for resources to give way to other tasks.

🔹 2. Thread vs Process

🔥 Real-Life Analogy:

• Process = Restaurant 🍽

• Threads = Waiters serving tables 👨‍🍳

👉 Multiple waiters (threads) = faster service

📌 Important:

• Threads in the same process share memory

• Meaning: mabilis communication between them

🔹 3. How Threads Work (Scheduler + Context Switch)

🧠 Thread Scheduler

• OS decides which thread runs next

🔄 Context Switch

• Saving current thread → switching to another → then returning later

👉 Parang:

• You pause Netflix → do homework → balik ulit sa Netflix

📌 From page 1:
Context switching stores and restores thread state.

🔹 4. Main Thread in Java

• Every Java program starts with main thread

public static void main(String[] args)

👉 This is the starting point of everything

💡 You can create more threads to run tasks simultaneously

🔹 5. Ways to Create Threads (SUPER IMPORTANT 🔥)

✅ Method 1: Extend Thread Class

class MyThread extends Thread {
    public void run() {
        System.out.println("Running thread");
    }
}

👉 Then:

MyThread t = new MyThread();
t.start();

✅ Method 2: Implement Runnable Interface

class MyThread implements Runnable {
    public void run() {
        System.out.println("Running thread");
    }
}

👉 Then:

Thread t = new Thread(new MyThread());
t.start();

⚖️ Comparison

💡 In short:

Use Runnable if you want flexibility 💯

🔹 6. start() vs run() (COMMON CONFUSION ⚠)

👉 Important:

• start() → creates new thread
  

• run() → just runs like normal method if called directly
  

💡 In short, ganito lang ‘yan:

👉 start() = real multithreading

👉 run() = normal function lang

🔹 7. Thread Methods (Core Tools)

From page 2:

🔹 8. Thread Priority

• 
  Range: 1 (low) → 10 (high)
  

• 
  Default: 5
  

📌 From page 2:

• MIN_PRIORITY = 1
  

• MAX_PRIORITY = 10
  

• NORM_PRIORITY = 5
  

⚠ Important:

• 
  Higher priority ≠ guaranteed faster execution
  

• 
  It just has higher chance to run
  

🔹 9. Useful Thread Methods Explained

💤 sleep()

• 
  Pauses thread
  

Thread.sleep(3000); // 3 seconds

👉 Example:

• 
  Waiting before next action (like loading screen)
  

⏳ join()

• 
  Wait for another thread to finish
  

👉 Example:

• 
  Wait for download → then open file
  

🧬 isAlive()

• 
  Checks if thread is still running
  

t.isAlive(); // true or false

🔥 Example Flow (from pages 3–4)

• 
  Thread starts
  

• 
  Sleeps (pause)
  

• 
  Ends
  

• 
  Then check if alive → false
  

🔹 10. Thread.currentThread()

👉 Gets the currently running thread

Thread.currentThread().getName();

💡 Useful for debugging or tracking execution

🧠 QUICK SUMMARY (Memory Mode)

🔥 Core Idea:

🧩 Easy Memory Tricks

1. TPC Rule

• Thread = small task
  

• Process = container
  

• Concurrency = multitasking
  

2. Start vs Run

👉 “Start creates, Run executes”

3. Thread Creation

👉 “Extend OR Implement”

• 
  Extend Thread
  

• 
  Implement Runnable
  

4. Thread Methods Shortcut

👉 SRSP GGIJS

• 
  Start
  

• 
  Run
  

• 
  Sleep
  

• 
  Priority
  

• 
  Get/Set Name
  

• 
  Get/Set Priority
  

• 
  isAlive
  

• 
  Join
  

(Okay medyo sabog mnemonic but it works 😭)

🧠 FINAL RECAP (Super Simplified)

👉 Concurrency = sabay-sabay na tasks

👉 Threads = workers

👉 Process = whole system

👉 start() = new thread

👉 run() = actual work

👉 sleep/join/isAlive = control tools