todo/src/main/java/ru/kamask/pet/todo/TodoApp.java

@@ -1,18 +1,30 @@
 package ru.kamask.pet.todo;
 
 import ru.kamask.pet.todo.model.SimpleTask;
+import ru.kamask.pet.todo.repo.InMemoryTaskRepository;
 
 public class TodoApp {
 
-    @SuppressWarnings("unused")
     public static void main(String[] args) {
-        var task = new SimpleTask("TodoApp");
-        System.out.println(task);
+        var repo = new InMemoryTaskRepository();
 
-        task.markAsCompleted();
+        repo.save(new SimpleTask("Задача номер один"));
+        repo.save(new SimpleTask("Задача номер два"));
+        repo.save(new SimpleTask("Задача номер три"));
+        repo.save(new SimpleTask("Задача номер четыре"));
 
-        var taskData = task.data();
-        System.out.println(taskData);
+        System.out.println(repo.findAll());
+
+        var taskOption = repo.findById(2);
+        if (taskOption.isPresent()) {
+            SimpleTask task = (SimpleTask) taskOption.get();
+            task.markAsCompleted();
+            var data = task.data();
+            System.out.println(data);
+        }
+
+        repo.delete(1);
+        System.out.println(repo.findAll());
     }
 
 }

todo/src/main/java/ru/kamask/pet/todo/model/Task.java

@@ -11,6 +11,10 @@ public abstract class Task {
         this.title = title;
     }
 
+    public int id() {
+        return id;
+    }
+
     @Override
     public String toString() {
         return String.format("Задача: id - %d, title: \"%s\"", id, title);

todo/src/main/java/ru/kamask/pet/todo/repo/InMemoryTaskRepository.java

@@ -0,0 +1,33 @@
+package ru.kamask.pet.todo.repo;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+
+import ru.kamask.pet.todo.model.Task;
+
+public class InMemoryTaskRepository implements TaskRepository {
+    private Map<Integer, Task> storage = new HashMap<>();
+
+    @Override
+    public void save(Task task) {
+        storage.put(task.id(), task);
+    }
+
+    @Override
+    public Optional<Task> findById(int id) {
+        return Optional.ofNullable(storage.get(id));
+    }
+
+    @Override
+    public List<Task> findAll() {
+        return new ArrayList<>(storage.values());
+    }
+
+    @Override
+    public void delete(int id) {
+        storage.remove(id);
+    }
+}

todo/src/main/java/ru/kamask/pet/todo/repo/TaskRepository.java

@@ -0,0 +1,16 @@
+package ru.kamask.pet.todo.repo;
+
+import java.util.List;
+import java.util.Optional;
+
+import ru.kamask.pet.todo.model.Task;
+
+public interface TaskRepository {
+    void save(Task task);
+
+    Optional<Task> findById(int id);
+
+    List<Task> findAll();
+
+    void delete(int id);
+}