Merge remote-tracking branch 'origin/main'

# Conflicts:
#	.gitignore

src/main/java/jvm/Calculation.java

@@ -0,0 +1,68 @@
+package jvm;
+import java.lang.System; // Import System for nanoTime and printf
+
+/**
+ * A Java class to replicate the calculation performed by the Python script.
+ */
+public class Calculation {
+
+    /**
+     * Performs the iterative calculation.
+     *
+     * @param iterations The number of iterations for the loop.
+     * @param param1     The first parameter used in the calculation.
+     * @param param2     The second parameter used in the calculation.
+     * @return The result of the calculation.
+     */
+    public static double calculate(int iterations, int param1, int param2) {
+        // Initialize the result as a double
+        double result = 1.0;
+
+        // Loop from 1 to iterations (inclusive)
+        for (int i = 1; i <= iterations; i++) {
+            // Calculate the first value of j
+            // Use double for j to ensure floating-point arithmetic
+            double jMinus = (double)i * param1 - param2;
+            // Subtract 1.0 / jMinus from the result (use 1.0 for double division)
+            result -= (1.0 / jMinus);
+
+            // Calculate the second value of j
+            double jPlus = (double)i * param1 + param2;
+            // Add 1.0 / jPlus to the result
+            result += (1.0 / jPlus);
+        }
+        // Return the final calculated result
+        return result;
+    }
+
+    /**
+     * The main entry point of the program.
+     *
+     * @param args Command line arguments (not used).
+     */
+    public static void main(String[] args) {
+        // Define the parameters for the calculation
+        final int ITERATIONS = 100_000_000; // Use underscore for readability (Java 7+)
+        final int PARAM1 = 4;
+        final int PARAM2 = 1;
+
+        // Record the start time using System.nanoTime() for higher precision
+        long startTime = System.nanoTime();
+
+        // Perform the calculation and multiply the result by 4.0
+        double finalResult = calculate(ITERATIONS, PARAM1, PARAM2) * 4.0;
+
+        // Record the end time
+        long endTime = System.nanoTime();
+
+        // Calculate the duration in nanoseconds
+        long durationNanos = endTime - startTime;
+        // Convert the duration to seconds (as a double)
+        double durationSeconds = durationNanos / 1_000_000_000.0;
+
+        // Print the final result, formatted to 12 decimal places
+        System.out.printf("Result: %.12f%n", finalResult);
+        // Print the execution time, formatted to 6 decimal places
+        System.out.printf("Execution Time: %.6f seconds%n", durationSeconds);
+    }
+}

src/main/java/jvm/Calculation2.java

@@ -0,0 +1,166 @@
+package jvm;
+import java.lang.System; // Import System for nanoTime and printf
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+
+/**
+ * A Java class to replicate the calculation performed by the Python script,
+ * optimized using multithreading.
+ */
+public class Calculation2 {
+
+    /**
+     * Represents a task that calculates a partial sum for a given range of iterations.
+     * Implements Callable so it can be executed by an ExecutorService and return a result.
+     */
+    private static class PartialCalculator implements Callable<Double> {
+        private final int startIteration;
+        private final int endIteration;
+        private final int param1;
+        private final int param2;
+
+        /**
+         * Constructor for the partial calculator task.
+         * @param startIteration The starting iteration (inclusive).
+         * @param endIteration The ending iteration (exclusive).
+         * @param param1 The first parameter for calculation.
+         * @param param2 The second parameter for calculation.
+         */
+        public PartialCalculator(int startIteration, int endIteration, int param1, int param2) {
+            this.startIteration = startIteration;
+            this.endIteration = endIteration;
+            this.param1 = param1;
+            this.param2 = param2;
+        }
+
+        /**
+         * The computation performed by this task. Calculates the sum for the assigned range.
+         * @return The partial sum for the range.
+         */
+        @Override
+        public Double call() {
+            double partialSum = 0.0;
+            // Loop through the assigned range of iterations
+            // Note: loop goes up to < endIteration
+            for (int i = startIteration; i < endIteration; i++) {
+                // Calculate the first value of j
+                double jMinus = (double)i * param1 - param2;
+                // Subtract 1.0 / jMinus from the partial sum
+                partialSum -= (1.0 / jMinus);
+
+                // Calculate the second value of j
+                double jPlus = (double)i * param1 + param2;
+                // Add 1.0 / jPlus to the partial sum
+                partialSum += (1.0 / jPlus);
+            }
+            return partialSum;
+        }
+    }
+
+    /**
+     * Performs the iterative calculation using multiple threads.
+     *
+     * @param iterations The total number of iterations for the loop.
+     * @param param1     The first parameter used in the calculation.
+     * @param param2     The second parameter used in the calculation.
+     * @param numThreads The number of threads to use for the calculation.
+     * @return The result of the calculation.
+     * @throws InterruptedException If thread execution is interrupted.
+     * @throws ExecutionException If computation threw an exception.
+     */
+    public static double calculateParallel(int iterations, int param1, int param2, int numThreads)
+            throws InterruptedException, ExecutionException {
+
+        // Create a fixed-size thread pool
+        ExecutorService executor = Executors.newFixedThreadPool(numThreads);
+        // List to hold the Future objects representing the results of each task
+        List<Future<Double>> futureResults = new ArrayList<>();
+
+        // Calculate the approximate number of iterations per thread
+        int iterationsPerThread = iterations / numThreads;
+        int start = 1; // Start iteration from 1
+
+        // Divide the work and submit tasks to the executor
+        for (int i = 0; i < numThreads; i++) {
+            int end = start + iterationsPerThread;
+            // For the last thread, ensure it covers all remaining iterations
+            if (i == numThreads - 1) {
+                end = iterations + 1; // Go up to iterations (inclusive)
+            }
+            // Ensure end doesn't exceed the total iterations + 1 boundary
+            if (end > iterations + 1) {
+                end = iterations + 1;
+            }
+
+            // Create and submit the task for the calculated range
+            // The loop inside PartialCalculator runs from start (inclusive) to end (exclusive)
+            Callable<Double> task = new PartialCalculator(start, end, param1, param2);
+            futureResults.add(executor.submit(task));
+
+            // Set the start for the next chunk
+            start = end;
+        }
+
+        // Initialize the total result (starting from the base 1.0)
+        double totalResult = 1.0;
+        // Retrieve results from each Future and add to the total result
+        for (Future<Double> future : futureResults) {
+            // future.get() blocks until the result is available
+            totalResult += future.get();
+        }
+
+        // Shut down the executor service gracefully
+        executor.shutdown();
+
+        // Return the final combined result
+        return totalResult;
+    }
+
+    /**
+     * The main entry point of the program.
+     *
+     * @param args Command line arguments (not used).
+     */
+    public static void main(String[] args) {
+        // Define the parameters for the calculation
+        final int ITERATIONS = 100_000_000;
+        final int PARAM1 = 4;
+        final int PARAM2 = 1;
+        // Determine the number of threads based on available processors
+        final int NUM_THREADS = Runtime.getRuntime().availableProcessors();
+
+        System.out.println("Using " + NUM_THREADS + " threads.");
+
+        // Record the start time
+        long startTime = System.nanoTime();
+
+        double finalResult = 0;
+        try {
+            // Perform the parallel calculation and multiply the result by 4.0
+            finalResult = calculateParallel(ITERATIONS, PARAM1, PARAM2, NUM_THREADS) * 4.0;
+
+            // Record the end time
+            long endTime = System.nanoTime();
+
+            // Calculate the duration
+            long durationNanos = endTime - startTime;
+            double durationSeconds = durationNanos / 1_000_000_000.0;
+
+            // Print the final result and execution time
+            System.out.printf("Result: %.12f%n", finalResult);
+            System.out.printf("Execution Time: %.6f seconds%n", durationSeconds);
+
+        } catch (InterruptedException | ExecutionException e) {
+            // Handle potential exceptions during parallel execution
+            System.err.println("Calculation failed: " + e.getMessage());
+            e.printStackTrace();
+            // Ensure System.exit is not used in production code without careful consideration
+            // System.exit(1);
+        }
+    }
+}

src/main/java/jvm/SpeedTest.java

@@ -0,0 +1,36 @@
+package jvm;
+
+/**
+ * it converts from python code
+ * just check performance differences between python and java
+ */
+public class SpeedTest {
+
+    public double calculate(int iter, int param1, int param2) {
+        double result = 1.0;
+
+        for (int i = 1; i <= iter; i++) {
+            double jMinus = (double)i * param1 - param2;
+            // Subtract 1.0 / jMinus from the result (use 1.0 for double division)
+            result -= (1.0 / jMinus);
+
+            // Calculate the second value of j
+            double jPlus = (double)i * param1 + param2;
+            // Add 1.0 / jPlus to the result
+            result += (1.0 / jPlus);
+        }
+
+        return result;
+    }
+
+    public static void main(String[] args) {
+        SpeedTest speedTest = new SpeedTest();
+        long start = System.nanoTime();
+        double result = speedTest.calculate(100_000_000, 4, 1) * 4.0;
+        System.out.println(result);
+        long end = System.nanoTime();
+        long durationNanos = end - start;
+        double durationSeconds = durationNanos / 1_000_000_000.0;
+        System.out.println( durationSeconds );
+    }
+}

src/main/java/jvm/VolatileTest.java

@@ -0,0 +1,42 @@
+package jvm;
+
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.locks.ReentrantLock;
+
+public class VolatileTest {
+
+    public  static  volatile int race = 0;
+    private static final Object lock = new Object();
+    private static final ReentrantLock lock1 = new ReentrantLock();
+    public static AtomicInteger race1 = new AtomicInteger(0);
+
+    public static void increase() {
+//       synchronized (lock) {
+//           race++;
+//       }
+        race1.getAndAdd(1);
+        lock1.lock();
+        race++;
+        lock1.unlock();
+    }
+
+    private static final int THREADS_COUNT = 20;
+
+    static void main() {
+        Thread[] threads = new Thread[THREADS_COUNT];
+        for (int i = 0; i < THREADS_COUNT; i++) {
+            threads[i] = new Thread(() -> {
+                for (int j = 0; j < 1000; j++) {
+                    increase();
+                }
+            });
+            threads[i].start();
+        }
+        // for idea only. otherwise should be 1
+        while (Thread.activeCount() > 2) {
+            Thread.yield();
+        }
+        System.out.println(race);
+        System.out.println(race1.get());
+    }
+}

src/main/java/loader/CustomLoader.java

@@ -0,0 +1,56 @@
+
+package loader;
+
+import java.io.*;
+
+public class CustomLoader extends ClassLoader{
+
+    private String classPath;
+
+    public CustomLoader(String classPath) {
+        this.classPath = classPath;
+    }
+
+    private byte[] loadClassBytes(String className) {
+        String path = STR."\{classPath}\{File.separatorChar}\{className.replace('.', File.separatorChar)}.class".trim();
+//        File file = new File("C:\\Users\\wjluk\\projects\\java_multithread\\src\\main\\java\\loader\\LoaderTest.class");
+        File file = new File(path);
+        System.out.println(file.exists());
+        try (InputStream is = new FileInputStream(path);
+             ByteArrayOutputStream baos = new ByteArrayOutputStream()) {
+            byte[] buffer = new byte[4096];
+            int bytesRead;
+            while ((bytesRead = is.read(buffer)) != -1) {
+                baos.write(buffer, 0, bytesRead);
+            }
+            return baos.toByteArray();
+        } catch (IOException e) {
+            return null;
+        }
+    }
+
+
+    @Override
+    protected Class<?> findClass(String name) throws ClassNotFoundException {
+        byte[] classBytes = loadClassBytes(name);
+        if (classBytes == null) {
+            throw new ClassNotFoundException();
+        }
+        return defineClass(name, classBytes, 0, classBytes.length);
+    }
+
+    static void main(String[] args) throws Exception {
+        CustomLoader loader = new CustomLoader(" D:\\");
+        Class<?> clazz = loader.loadClass("LoaderTest");
+        Object obj = clazz.newInstance();
+        clazz.getMethod("greeting").invoke(obj);
+        System.out.println(clazz.getClassLoader());
+
+        System.out.println("---------------------for parent loader-------------------");
+        ClassLoader classLoader = loader.getClass().getClassLoader();
+        while (classLoader != null) {
+            System.out.println( "\t" + classLoader);
+            classLoader = classLoader.getParent();
+        }
+    }
+}