created own ArrayList collection which implements our List interface …

src/main/java/core/basesyntax/ArrayList.java

@@ -1,48 +1,115 @@
 package core.basesyntax;
 
+import java.util.NoSuchElementException;
+
 public class ArrayList<T> implements List<T> {
+    private static final int DEFAULT_CAPACITY = 10;
+    private static final double RESIZE_COEFFICIENT = 1.5;
+    private Object[] elements;
+    private int size;
+
+    public ArrayList() {
+        this.elements = new Object[DEFAULT_CAPACITY];
+    }
+
     @Override
     public void add(T value) {
-
+        ensureCapacity();
+        elements[size++] = value;
     }
 
     @Override
     public void add(T value, int index) {
-
+        if (index < 0 || index > size) {
+            throw new ArrayListIndexOutOfBoundsException("Index outed of bounds, Index: " + index
+                    + ", Size: "
+                    + size);
+        }
+        ensureCapacity();
+        System.arraycopy(elements, index, elements, index + 1, size - index);
+        elements[index] = value;
+        size++;
     }
 
     @Override
     public void addAll(List<T> list) {
-
+        for (int i = 0; i < list.size(); i++) {
+            add(list.get(i));
+        }
     }
 
     @Override
     public T get(int index) {
-        return null;
+        if (index < 0 || index >= size) {
+            throw new ArrayListIndexOutOfBoundsException("Index outed of bounds, Index: " + index
+                    + ", Size: "
+                    + size);
+        }
+        return (T) elements[index];
     }
 
     @Override
     public void set(T value, int index) {
-
+        if (index < 0 || index >= size) {
+            throw new ArrayListIndexOutOfBoundsException("Index outed of bounds, Index: " + index
+                    + ", Size: "
+                    + size);
+        }
+        elements[index] = value;
     }
 
     @Override
     public T remove(int index) {
-        return null;
+        if (index < 0 || index >= size) {
+            throw new ArrayListIndexOutOfBoundsException("Index outed of bounds, Index: " + index
+                    + ", Size: "
+                    + size);
+        }
+        T removedValue = (T) elements[index];
+        System.arraycopy(elements, index + 1, elements, index, size - index - 1);
+        elements[--size] = null;
+        return removedValue;
     }
 
     @Override
     public T remove(T element) {
-        return null;
+        if (element == null) {
+            for (int i = 0; i < size; i++) {
+                if (elements[i] == null) {
+                    return remove(i);
+                }
+            }
+            throw new NoSuchElementException("Element not found");
+        }
+
+        for (int i = 0; i < size; i++) {
+            if (element.equals(elements[i])) {
+                return remove(i);
+            }
+        }
+        throw new NoSuchElementException("Element not found");
     }
 
     @Override
     public int size() {
-        return 0;
+        return size;
     }
 
     @Override
     public boolean isEmpty() {
-        return false;
+        return size == 0;
+    }
+
+    private void resize() {
+        int newCapacity = (int) (elements.length * RESIZE_COEFFICIENT);
+        Object[] newElements = new Object[newCapacity];
+        System.arraycopy(elements, 0, newElements, 0, size);
+        elements = newElements;
+    }
+
+    private void ensureCapacity() {
+        if (size == elements.length) {
+            resize();
+        }
     }
 }