Report.md

@@ -0,0 +1,92 @@
+
+## Question 1: `start()` vs `run()`
+
+### What output do you get from the program?
+
+
+
+The first call (`t1.run()`) prints `Running in: main` because it executes on the **main thread** directly — no new thread is created. The second call (`t2.start()`) properly spawns a new thread, so it prints `Running in: Thread-2`.
+
+The `Thread.sleep(100)` between the two calls ensures `t2`'s output isn't interleaved with the first, but the ordering of the second line is still technically non-deterministic (it will almost always appear after `"Calling start()"`).
+
+### What's the difference between `start()` and `run()`?
+
+| | `run()` | `start()` |
+|---|---|---|
+| **Execution** | Runs on the **calling thread** (like a normal method call) | Spawns a **new OS thread** and runs `run()` on it |
+| **Concurrency** | None — sequential, blocking | Concurrent — the calling thread continues immediately |
+| **Thread name** | Uses the calling thread's name (`main`) | Uses the new thread's name (`Thread-2`) |
+| **Thread lifecycle** | Does not transition the thread to `RUNNABLE` state | Properly starts the thread lifecycle |
+
+Calling `run()` directly is just a regular method call. Only `start()` actually creates a new thread.
+
+---
+
+## Question 2: Daemon Threads
+
+### What output do you get from the program?
+
+```
+Main thread ends.
+Daemon thread running...
+Daemon thread running...
+(possibly a few more lines, then the program exits abruptly)
+```
+
+The exact number of "Daemon thread running..." lines is non-deterministic — typically 0 to 2. The JVM shuts down as soon as the **main thread** finishes, which kills all remaining daemon threads immediately, regardless of what they're doing.
+
+### What happens if you remove `thread.setDaemon(true)`?
+
+The thread becomes a regular (non-daemon) **user thread**. The JVM will **not exit** until all user threads complete. In this case, the loop runs all 20 iterations (taking ~10 seconds), printing `"Daemon thread running..."` 20 times before the program ends.
+
+### Real-life use cases of daemon threads
+
+- **Garbage Collector** – The JVM's own GC runs as a daemon thread; it should never prevent the JVM from shutting down.
+- **Background logging** – Flushing logs or metrics to a file/server periodically, where losing the last few entries on shutdown is acceptable.
+- **Heartbeat / keep-alive threads** – Sending periodic pings to a server while the application is alive.
+- **Cache invalidation** – A background thread that evicts stale entries from an in-memory cache.
+- **Auto-save** – Periodically saving a draft in an editor; the user closing the app shouldn't be blocked by this.
+
+---
+
+## Question 3: A Shorter Way to Create Threads (Lambda)
+
+### What output do you get from the program?
+
+```
+Thread is running using a ...!
+```
+
+(Printed from the newly spawned thread.)
+
+### What is the `() -> { ... }` syntax called?
+
+It is called a **lambda expression** (introduced in Java 8). It provides a concise way to implement a **functional interface** — an interface with exactly one abstract method. Since `Runnable` has only one method (`run()`), a lambda can be used anywhere a `Runnable` is expected.
+
+### How is this different from extending `Thread` or implementing `Runnable`?
+
+| Approach | Code required | Reusability | Notes |
+|---|---|---|---|
+| `extends Thread` | Full class definition | Low — must subclass `Thread`, can't extend anything else | Tightly couples logic to thread machinery |
+| `implements Runnable` | Full class + `new Thread(r)` | Higher — decouples task from thread | Preferred for named/reusable task classes |
+| **Lambda** | One-liner inline | Low — anonymous, inline only | Best for short, one-off tasks |
+
+The lambda approach is essentially **anonymous shorthand for `implements Runnable`** — the compiler generates an implementation of `Runnable.run()` under the hood. It is the most concise option but is best suited for simple, short tasks. For complex or reusable tasks, a named class implementing `Runnable` is clearer.
+
+```java
+// These three are functionally equivalent:
+
+// 1. Class extending Thread
+class MyThread extends Thread {
+    public void run() { System.out.println("Running"); }
+}
+new MyThread().start();
+
+// 2. Anonymous Runnable
+new Thread(new Runnable() {
+    public void run() { System.out.println("Running"); }
+}).start();
+
+// 3. Lambda (shortest)
+new Thread(() -> System.out.println("Running")).start();
+```

src/main/java/DownloadWorker.java

@@ -1,12 +1,5 @@
 import java.util.Random;
 
-/**
- * Simulates downloading a single chunk of a file.
- *
- * <p>This class is intentionally provided as a skeleton for students.
- * The main multithreading and simulation logic should be completed
- * in the run() method.</p>
- */
 public class DownloadWorker implements Runnable {
 
     private final ChunkStatus chunkStatus;
@@ -21,23 +14,32 @@ public class DownloadWorker implements Runnable {
 
     @Override
     public void run() {
-        // TODO: Record the chunk start time in chunkStatus.
+
         double downloaded = 0.0;
-
+        long startTime = System.currentTimeMillis();
-        // TODO: Print a message that this chunk has started downloading.
+        chunkStatus.setStartTimeMs(startTime);
-
+        System.out.println("Chunk: " + chunkStatus.getChunkId() + " has started downloading.");
         while (downloaded < chunkStatus.getChunkSizeMB()) {
-            // TODO: Generate a random sleep delay between min and max delay.
+
-            // TODO: Sleep for that delay.
+            long randomSleep = random.nextLong(config.getMinStepDelayMs(), config.getMaxStepDelayMs());
-            // TODO: Generate a random download amount for this step.
+
-            // TODO: Increase downloaded, but do not go beyond chunk size.
+            try {
-            // TODO: Save the updated downloaded value into chunkStatus.
+                Thread.sleep(randomSleep);
-            // TODO: Optionally print step-by-step progress.
+            }
+            catch (InterruptedException e) {
+                System.out.println(e.getMessage());
+            }
+
+            double down = random.nextDouble();
+            downloaded = Math.min(downloaded + down, chunkStatus.getChunkSizeMB());
+            chunkStatus.setDownloadedMB(chunkStatus.getDownloadedMB() + down);
         }
 
-        // TODO: Mark the chunk as completed.
+        chunkStatus.setCompleted(true);
-        // TODO: Record the chunk end time in chunkStatus.
+        Long endTime = System.currentTimeMillis();
-        // TODO: Print a message that this chunk has finished downloading.
+        chunkStatus.setEndTimeMs(endTime);
+        System.out.println("Chunk: " + chunkStatus.getChunkId() +
+                " has completed downloading (" + chunkStatus.getDownloadDurationMs() +" ms)");
     }
 
 }

src/main/java/Main.java

@@ -1,5 +1,6 @@
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Random;
 
 public class Main {
     public static void main(String[] args) {
@@ -19,13 +20,13 @@ public class Main {
         System.out.println("Chunk count: " + config.getChunkCount());
         System.out.println();
 
-        // 2. Create chunks
+
         List<ChunkStatus> chunks = ChunkUtils.createChunks(
                 config.getTotalSizeMB(),
                 config.getChunkCount()
         );
 
-        // 3. Create worker threads
+
         List<Thread> workerThreads = new ArrayList<>();
 
         for (ChunkStatus chunk : chunks) {
@@ -34,50 +35,37 @@ public class Main {
 
             workerThreads.add(workerThread);
 
-            // TODO:
+            System.out.println("Assigned Worker-" + chunk.getChunkId()
-            // Students may print helpful debug information here,
+                    + " to chunk #" + chunk.getChunkId()
-            // for example which chunk is assigned to which worker thread.
+                    + " (" + chunk.getChunkSizeMB() + " MB)");
         }
 
-        // 4. Create and start monitor thread
+        System.out.println();
+
         ProgressMonitor monitor = new ProgressMonitor(config, chunks);
         Thread monitorThread = new Thread(monitor, "Progress-Monitor");
+        
+        monitorThread.start();
 
-        // TODO:
+        for (Thread workerThread : workerThreads) {
-        // Start the monitor thread before starting the workers
+            workerThread.start();
-        // so that progress can be displayed while downloading happens.
+        }
-        //
-        // Example idea:
-        // monitorThread.start();
 
-        // 5. Start worker threads
+        for (Thread workerThread : workerThreads) {
-        // TODO:
+            try {
-        // Start each worker thread in workerThreads.
+                workerThread.join();
-        // Use a loop and call start() on each thread.
+            } catch (InterruptedException e) {
+                System.out.println("Thread was interrupted: " + e.getMessage());
+            }
+        }
 
-        // 6. Wait for workers to finish
+        try {
-        // TODO:
+            monitorThread.join();
-        // Wait for all worker threads to complete by calling join().
+        }
-        // This should be done inside a try-catch block for InterruptedException.
+        catch (InterruptedException e) {
-        //
+            System.out.println("Thread was interrupted: " + e.getMessage());
-        // Hint:
+        }
-        // for (Thread thread : workerThreads) {
-        //     thread.join();
-        // }
 
-        // TODO:
-        // After all workers finish, the monitor thread may also need to stop.
-        // Depending on how ProgressMonitor is implemented, students may:
-        // - wait for it to finish on its own, or
-        // - add a stopping mechanism in ProgressMonitor later.
-        //
-        // If your monitor finishes automatically, you may join it here.
-
-        // NOTE:
-        // this final report may show 0 progress because no worker has actually run yet.
-        // Until students complete the thread start/join TODOs above,
-
-        // 7. Print final report
         System.out.println();
         System.out.println("=== Final Report ===");
 
@@ -91,17 +79,15 @@ public class Main {
                 completedChunks++;
             }
 
-            System.out.println(
+            System.out.printf("  Chunk %d: %.2f/%.0f MB | Duration: %d ms%n",
-                    "Chunk " + chunk.getChunkId()
+                    chunk.getChunkId(), chunk.getDownloadedMB(),
-                            + ": " + chunk.getDownloadedMB()
+                    chunk.getChunkSizeMB(), chunk.getDownloadDurationMs());
-                            + "/" + chunk.getChunkSizeMB()
+
-                            + " MB"
-            );
         }
 
         System.out.println();
-        System.out.println("Completed chunks: " + completedChunks + "/" + chunks.size());
+        System.out.println("Completed chunks : " + completedChunks + "/" + chunks.size());
-        System.out.println("Downloaded total: " + downloadedMB + "/" + config.getTotalSizeMB() + " MB");
+        System.out.printf("Downloaded total : %.2f/%d MB%n", downloadedMB, config.getTotalSizeMB());
-        System.out.println("Simulation finished.");
+
     }
 }

src/main/java/ProgressMonitor.java

@@ -16,16 +16,7 @@ public class ProgressMonitor implements Runnable {
 
     @Override
     public void run() {
-        // TODO:
+        double previousProgress = 0.0;
-        // Repeatedly check chunk progress until all chunks are completed.
-        // In each loop:
-        // 1. Read the downloaded size from every chunk
-        // 2. Add all downloaded amounts to totalDownloadedMB
-        // 3. Count completed chunks
-        // 4. Print a progress message
-        // 5. If completedChunks == chunks.size(), print a final monitor message and stop
-        // 6. Otherwise sleep for monitorDelayMs and continue
-
 
         while (true) {
             double totalDownloadedMB = 0.0;
@@ -44,25 +35,49 @@ public class ProgressMonitor implements Runnable {
                 percent = (totalDownloadedMB * 100.0) / totalSizeMB;
             }
 
-            System.out.printf(
+
-                    "Progress for %s: %.1f/%.1f MB (%.2f%%), completed chunks: %d/%d%n",
+            double deltaMB = totalDownloadedMB - previousProgress;
-                    fileName,
+            double speedMBps = deltaMB / (monitorDelayMs / 1000.0);
-                    totalDownloadedMB,
+            previousProgress = totalDownloadedMB;
-                    (double) totalSizeMB,
-                    percent,
-                    completedChunks,
-                    chunks.size()
-            );
 
 
-            // TODO:
+            double remainingMB = totalSizeMB - totalDownloadedMB;
-            // If all chunks are completed, print a final message and exit the loop
+            long etaSeconds = (speedMBps > 0) ? (long)(remainingMB / speedMBps) : 0;
 
-            try {
+
-                Thread.sleep(monitorDelayMs);
+            int barWidth = 30;
-            } catch (InterruptedException e) {
+            int filled = (int)(percent / 100.0 * barWidth);
-                System.out.println("Progress monitor interrupted.");
+            filled = Math.min(filled, barWidth);
-                return;
+            String bar = "=".repeat(filled) + (filled < barWidth ? ">" : "") + " ".repeat(Math.max(0, barWidth - filled - 1));
+
+
+            System.out.printf("\r[%-30s] %5.1f%% | %5.1f/%d MB | Speed: %.2f MB/s | ETA: %ds | Chunks: %d/%d   ",
+                    bar, percent, totalDownloadedMB, totalSizeMB,
+                    speedMBps, etaSeconds,
+                    completedChunks, chunks.size());
+
+//            System.out.printf(
+//                    "Progress for %s: %.1f/%.1f MB (%.2f%%), completed chunks: %d/%d%n",
+//                    fileName,
+//                    totalDownloadedMB,
+//                    (double) totalSizeMB,
+//                    percent,
+//                    completedChunks,
+//                    chunks.size()
+//            );
+
+
+            if (completedChunks == chunks.size()) {
+                System.out.println("download completed!");
+                break;
+            } else {
+
+                try {
+                    Thread.sleep(monitorDelayMs);
+                } catch (InterruptedException e) {
+                    System.out.println("Progress monitor interrupted.");
+                    return;
+                }
             }
         }
     }

src/main/resources/download_config.txt

@@ -1,7 +1,7 @@
 fileName=movie.mkv
 totalSizeMB=120
-chunkCount=6
+chunkCount=10
-minStepDelayMs=80
+minStepDelayMs=200
-maxStepDelayMs=200
+maxStepDelayMs=600
-minStepDownloadMB=2
+minStepDownloadMB=.1
-maxStepDownloadMB=6
+maxStepDownloadMB=.4