basic

.idea/misc.xml

@@ -8,7 +8,7 @@
       </list>
     </option>
   </component>
-  <component name="ProjectRootManager" version="2" languageLevel="JDK_21" default="true" project-jdk-name="21" project-jdk-type="JavaSDK">
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_26" project-jdk-name="26" project-jdk-type="JavaSDK">
     <output url="file://$PROJECT_DIR$/out" />
   </component>
 </project>

Report.md

@@ -0,0 +1,142 @@
+
+# `start()` vs `run()`
+
+## Output
+
+The output will be similar to:
+
+```text
+Calling run()
+Running in: main
+Calling start()
+Running in: Thread-2
+```
+
+(The exact order of the last two lines may vary slightly because `start()` creates a new thread that runs independently.)
+
+## Why?
+
+When `t1.run()` is called, the `run()` method is executed like a normal method call. It does not create a new thread. Since `main()` is the thread currently executing the code, `Thread.currentThread().getName()` returns `main`.
+
+When `t2.start()` is called, Java creates a new thread and the JVM schedules that thread to execute the `run()` method. Because the new thread was created with the name `"Thread-2"`, the output shows `Thread-2` as the executing thread.
+
+## Difference between `start()` and `run()`
+
+The main difference is that `start()` creates a new thread of execution, while `run()` only executes the method in the current thread.
+
+* Calling `run()` directly does not start a new thread. The code runs sequentially in the same thread that called it.
+* Calling `start()` creates a new thread and then internally calls the `run()` method on that new thread.
+* `start()` allows multiple threads to run concurrently, while `run()` behaves like a normal method call.
+
+In this example, `t1.run()` runs inside the `main` thread, but `t2.start()` runs inside a separate thread named `Thread-2`.
+
+## 2.Daemon Threads
+
+## Output
+
+The output will usually be:
+
+```text
+Main thread ends.
+```
+
+Sometimes it may also print one or more lines like:
+
+```text
+Daemon thread running...
+Main thread ends.
+```
+
+The exact output depends on the timing of the JVM shutting down.
+
+## Why?
+
+The thread is marked as a daemon thread using:
+
+```java
+thread.setDaemon(true);
+```
+
+Daemon threads run in the background and do not prevent the JVM from exiting. When the `main` thread finishes, there are no remaining non-daemon threads, so the JVM terminates. As a result, the daemon thread may be stopped before it completes its loop of printing messages 20 times.
+
+## What happens if `thread.setDaemon(true)` is removed?
+
+If `setDaemon(true)` is removed, the thread becomes a normal (user) thread. The JVM will wait for this thread to finish before shutting down.
+
+The output will look something like:
+
+```text
+Main thread ends.
+Daemon thread running...
+Daemon thread running...
+Daemon thread running...
+...
+```
+
+The daemon thread will continue running until the loop completes, even though the `main` thread has already finished.
+
+## Real-life use cases of daemon threads
+
+Daemon threads are useful for background tasks that should automatically stop when the main application ends. Some examples include:
+
+* **Garbage collection:** The JVM uses background daemon threads to manage memory cleanup.
+* **Background monitoring:** Applications can use daemon threads to monitor system resources, logs, or application status.
+* **Auto-save features:** A text editor or IDE might use a daemon thread to periodically save temporary data.
+* **Cache cleanup:** A server application might run a daemon thread to remove expired cache entries.
+* **Scheduled background tasks:** Tasks like checking for updates or refreshing data can run as daemon threads.
+
+Daemon threads are mainly used for tasks that support the main application but are not essential for the application to finish running.
+
+# 3. A Shorter Way to Create Threads
+
+## Output
+
+The output will be:
+
+```text id="q7k4m3"
+Thread is running using a ...!
+```
+
+The message is printed from the new thread created by calling `thread.start()`.
+
+## What is the `() -> { ... }` syntax called?
+
+The `() -> { ... }` syntax is called a **lambda expression** in Java.
+
+A lambda expression is a shorter way to write an implementation of a functional interface. In this example, it replaces the need to create a separate class that implements `Runnable`.
+
+The code:
+
+```java id="9xw2aq"
+() -> {
+    System.out.println("Thread is running using a ...!");
+}
+```
+
+acts as the implementation of the `Runnable` interface's `run()` method.
+
+## How is this different from creating a class that extends `Thread` or implements `Runnable`?
+
+Using a lambda expression makes the code shorter and easier to read because it avoids creating an extra class.
+
+With `implements Runnable`, we normally create a separate class:
+
+```java id="6g5v1p"
+class MyRunnable implements Runnable {
+    public void run() {
+        System.out.println("Thread running");
+    }
+}
+```
+
+With a lambda expression, the same idea can be written directly:
+
+```java id="v4c2km"
+Thread thread = new Thread(() -> {
+    System.out.println("Thread running");
+});
+```
+
+Extending `Thread` means creating a new class that inherits from the `Thread` class and overrides the `run()` method. This gives more control over the thread object but is less flexible because Java only allows a class to extend one class.
+
+Using `Runnable` or a lambda expression is generally preferred because it separates the task being performed from the thread itself and allows the code to be more reusable.

src/main/java/DownloadWorker.java

@@ -1,12 +1,6 @@
 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 +15,74 @@ public class DownloadWorker implements Runnable {
 
     @Override
     public void run() {
-        // TODO: Record the chunk start time in chunkStatus.
+
+        chunkStatus.setStartTimeMs(System.currentTimeMillis());
         double downloaded = 0.0;
 
-        // TODO: Print a message that this chunk has started downloading.
+
+        System.out.println(Thread.currentThread().getName()
+                + " started downloading Chunk #" + chunkStatus.getChunkId()
+                + " (" + chunkStatus.getChunkSizeMB() + " MB)");
 
         while (downloaded < chunkStatus.getChunkSizeMB()) {
-            // TODO: Generate a random sleep delay between min and max delay.
+
-            // TODO: Sleep for that delay.
+            int delay = randomBetween(config.getMinStepDelayMs(), config.getMaxStepDelayMs());
-            // TODO: Generate a random download amount for this step.
+
-            // TODO: Increase downloaded, but do not go beyond chunk size.
+
-            // TODO: Save the updated downloaded value into chunkStatus.
+            try {
-            // TODO: Optionally print step-by-step progress.
+                Thread.sleep(delay);
+            } catch (InterruptedException e) {
+                System.out.println(Thread.currentThread().getName() + " was interrupted.");
+                Thread.currentThread().interrupt();
+                return;
+            }
+
+
+            double step = randomBetween(config.getMinStepDownloadMB(), config.getMaxStepDownloadMB());
+
+
+            downloaded += step;
+            if (downloaded > chunkStatus.getChunkSizeMB()) {
+                downloaded = chunkStatus.getChunkSizeMB();
+            }
+
+
+            chunkStatus.setDownloadedMB(downloaded);
+
+
+            System.out.printf("%s -> Chunk #%d: %.1f/%.1f MB (%.1f%%)%n",
+                    Thread.currentThread().getName(),
+                    chunkStatus.getChunkId(),
+                    downloaded,
+                    chunkStatus.getChunkSizeMB(),
+                    chunkStatus.getProgressPercentage());
         }
 
-        // TODO: Mark the chunk as completed.
+
-        // TODO: Record the chunk end time in chunkStatus.
+        chunkStatus.setCompleted(true);
-        // TODO: Print a message that this chunk has finished downloading.
+
+
+        chunkStatus.setEndTimeMs(System.currentTimeMillis());
+
+
+        System.out.println(Thread.currentThread().getName()
+                + " finished Chunk #" + chunkStatus.getChunkId()
+                + " in " + chunkStatus.getDownloadDurationMs() + " ms");
     }
 
+
+    private int randomBetween(int min, int max) {
+        if (min >= max) {
+            return min;
+        }
+        return min + random.nextInt(max - min + 1);
+    }
+
+
+    private double randomBetween(double min, double max) {
+        if (min >= max) {
+            return min;
+        }
+        return min + random.nextDouble() * (max - min);
+    }
 }

src/main/java/Main.java

@@ -34,50 +34,41 @@ public class Main {
 
             workerThreads.add(workerThread);
 
-            // TODO:
+            System.out.println("Assigned Chunk #" + chunk.getChunkId()
-            // Students may print helpful debug information here,
+                    + " (" + chunk.getChunkSizeMB() + " MB) to " + workerThread.getName());
-            // for example which chunk is assigned to which worker thread.
         }
 
-        // 4. Create and start monitor thread
+
         ProgressMonitor monitor = new ProgressMonitor(config, chunks);
         Thread monitorThread = new Thread(monitor, "Progress-Monitor");
 
-        // TODO:
-        // Start the monitor thread before starting the workers
-        // so that progress can be displayed while downloading happens.
-        //
-        // Example idea:
-        // monitorThread.start();
 
-        // 5. Start worker threads
+        monitorThread.start();
-        // TODO:
-        // Start each worker thread in workerThreads.
-        // Use a loop and call start() on each thread.
 
-        // 6. Wait for workers to finish
-        // TODO:
-        // Wait for all worker threads to complete by calling join().
-        // This should be done inside a try-catch block for InterruptedException.
-        //
-        // Hint:
-        // for (Thread thread : workerThreads) {
-        //     thread.join();
-        // }
 
-        // TODO:
+        for (Thread thread : workerThreads) {
-        // After all workers finish, the monitor thread may also need to stop.
+            thread.start();
-        // Depending on how ProgressMonitor is implemented, students may:
+        }
-        // - wait for it to finish on its own, or
+
-        // - add a stopping mechanism in ProgressMonitor later.
+
-        //
+        for (Thread thread : workerThreads) {
-        // If your monitor finishes automatically, you may join it here.
+            try {
+                thread.join();
+            } catch (InterruptedException e) {
+                System.out.println("Main thread interrupted while waiting for " + thread.getName());
+                Thread.currentThread().interrupt();
+            }
+        }
+
+
+        try {
+            monitorThread.join();
+        } catch (InterruptedException e) {
+            System.out.println("Main thread interrupted while waiting for monitor.");
+            Thread.currentThread().interrupt();
+        }
 
-        // 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 ===");
 

src/main/java/ProgressMonitor.java

@@ -1,5 +1,6 @@
 import java.util.List;
 
+
 public class ProgressMonitor implements Runnable {
 
     private final String fileName;
@@ -16,21 +17,11 @@ public class ProgressMonitor implements Runnable {
 
     @Override
     public void run() {
-        // TODO:
-        // 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;
             int completedChunks = 0;
 
+
             for (ChunkStatus chunk : chunks) {
                 totalDownloadedMB += chunk.getDownloadedMB();
 
@@ -44,6 +35,7 @@ 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",
                     fileName,
@@ -55,8 +47,11 @@ public class ProgressMonitor implements Runnable {
             );
 
 
-            // TODO:
+            if (completedChunks == chunks.size()) {
-            // If all chunks are completed, print a final message and exit the loop
+                System.out.println("Progress monitor: all chunks completed. Stopping monitor.");
+                return;
+            }
+
 
             try {
                 Thread.sleep(monitorDelayMs);