feat: add DoubleBuffer implementation and initial tests

Author: gaye-lamine

src/main/java/com/thealgorithms/datastructures/buffers/DoubleBuffer.java

@@ -0,0 +1,105 @@
+package com.thealgorithms.datastructures.buffers;
+
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicInteger;
+
+/**
+ * The {@code DoubleBuffer} class implements a double buffering mechanism.
+ * It maintains two buffers, allowing the program to switch between them.
+ * This class is useful for separating read/write operations and optimizing memory usage.
+ *
+ * @param <Item> The type of elements stored in the double buffer.
+ */
+public class DoubleBuffer<Item> {
+    private final Item[] primaryBuffer;
+    private final Item[] secondaryBuffer;
+    private final AtomicInteger primaryIndex;
+    private final AtomicInteger secondaryIndex;
+    private final int capacity;
+    private final AtomicBoolean isPrimaryActive;
+
+    /**
+     * Constructor to initialize the double buffer with a specified capacity.
+     *
+     * @param capacity The size of each buffer.
+     * @throws IllegalArgumentException if the capacity is zero or negative.
+     */
+    public DoubleBuffer(int capacity) {
+        if (capacity <= 0) {
+            throw new IllegalArgumentException("Buffer size must be positive");
+        }
+        // noinspection unchecked
+        this.primaryBuffer = (Item[]) new Object[capacity];
+        this.secondaryBuffer = (Item[]) new Object[capacity];
+        this.primaryIndex = new AtomicInteger(0);
+        this.secondaryIndex = new AtomicInteger(0);
+        this.capacity = capacity;
+        this.isPrimaryActive = new AtomicBoolean(true);
+    }
+
+    /**
+     * Checks if the active buffer is empty.
+     *
+     * @return {@code true} if the active buffer is empty, {@code false} otherwise.
+     */
+    public boolean isEmpty() {
+        return isPrimaryActive.get() ? primaryIndex.get() == 0 : secondaryIndex.get() == 0;
+    }
+
+    /**
+     * Switches between the primary and secondary buffers.
+     */
+    public void switchBuffer() {
+        isPrimaryActive.set(!isPrimaryActive.get());
+    }
+
+    /**
+     * Checks if the primary buffer is currently active.
+     *
+     * @return {@code true} if the primary buffer is active, {@code false} otherwise.
+     */
+    public boolean isPrimaryActive() {
+        return isPrimaryActive.get();
+    }
+
+    /**
+     * Adds an item to the active buffer.
+     *
+     * @param item The item to be added.
+     * @throws IllegalArgumentException if the item is null.
+     */
+    public void put(Item item) {
+        if (item == null) {
+            throw new IllegalArgumentException("Null items are not allowed");
+        }
+
+        if (isPrimaryActive.get()) {
+            if (primaryIndex.get() < capacity) {
+                primaryBuffer[primaryIndex.getAndIncrement()] = item;
+            }
+        } else {
+            if (secondaryIndex.get() < capacity) {
+                secondaryBuffer[secondaryIndex.getAndIncrement()] = item;
+            }
+        }
+    }
+
+    /**
+     * Retrieves and removes the item at the front of the active buffer.
+     *
+     * @return The item from the active buffer, or {@code null} if the buffer is empty.
+     */
+    public Item get() {
+        if (isPrimaryActive.get()) {
+            if (primaryIndex.get() == 0) {
+                return null;
+            }
+            return primaryBuffer[primaryIndex.decrementAndGet()];
+        } else {
+            if (secondaryIndex.get() == 0) {
+                return null;
+            }
+            return secondaryBuffer[secondaryIndex.decrementAndGet()];
+        }
+    }
+}

src/test/java/com/thealgorithms/datastructures/buffers/DoubleBufferTest.java

@@ -0,0 +1,71 @@
+package com.thealgorithms.datastructures.buffers;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+class DoubleBufferTest {
+
+    private DoubleBuffer<Integer> buffer;
+
+    @BeforeEach
+    void setUp() {
+        buffer = new DoubleBuffer<>(5);
+    }
+
+    @Test
+    void testInitialization() {
+        assertTrue(buffer.isPrimaryActive());
+        assertTrue(buffer.isEmpty());
+    }
+
+    @Test
+    void testPutAndGetFromPrimary() {
+        buffer.put(1);
+        buffer.put(2);
+        buffer.put(3);
+
+        assertEquals(3, buffer.get());
+        assertEquals(2, buffer.get());
+        assertEquals(1, buffer.get());
+        assertNull(buffer.get());
+    }
+
+    @Test
+    void testSwitchBuffers() {
+        buffer.put(1);
+        buffer.put(2);
+        buffer.switchBuffer();
+
+        // Now the buffer should be empty as we switched to the secondary buffer
+        assertTrue(buffer.isEmpty());
+
+        buffer.put(3);
+        assertEquals(3, buffer.get());
+
+        // Switch back to primary
+        buffer.switchBuffer();
+        assertEquals(2, buffer.get());
+        assertEquals(1, buffer.get());
+    }
+
+    @Test
+    void testEmptyBuffer() {
+        assertNull(buffer.get());
+        buffer.switchBuffer();
+        assertNull(buffer.get());
+    }
+
+    @Test
+    void testIllegalArguments() {
+        assertThrows(IllegalArgumentException.class, () -> new DoubleBuffer<>(0));
+        assertThrows(IllegalArgumentException.class, () -> new DoubleBuffer<>(-1));
+
+        DoubleBuffer<String> strBuffer = new DoubleBuffer<>(1);
+        assertThrows(IllegalArgumentException.class, () -> strBuffer.put(null));
+    }
+}