✅ To-Do List Application in Java

A console-based task manager written in Java using object-oriented programming. Supports adding, completing, deleting, and filtering tasks with no external libraries or frameworks.

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📋 Table of Contents

• Features
• Concepts Covered
• Project Structure
• How It Works
• Getting Started
• Usage
• Sample Output
• Limitations

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Features

Feature	Description
Add Task	Insert a new task by title
View All Tasks	Display all tasks with completion status
Mark Complete	Mark a pending task as done
Delete Task	Remove a task by its number
View Pending	Filter and show only incomplete tasks
View Completed	Filter and show only finished tasks

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Concepts Covered

• Classes & Objects — Task and TodoList are separate classes, each with a clear responsibility
• Encapsulation — Task fields are private; accessed only through public getter methods
• ArrayList — dynamic list with no fixed size limit; grows and shrinks automatically
• toString() override — controls how a Task prints ([✓] or [ ])
• Scanner — reads user input from the console with input type validation

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Project Structure

todo-list-java/
├── Main.java      # Contains Task, TodoList, and Main classes
└── README.md

All three classes are in a single file for simplicity. The file compiles and runs with one command.

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How It Works

Class Breakdown

┌─────────────────────────────────────────────┐
│  Task                                       │
│  ─────────────────────────────────────────  │
│  - title       : String  (private)          │
│  - isCompleted : boolean (private)          │
│  ─────────────────────────────────────────  │
│  + getTitle()    : String                   │
│  + isCompleted() : boolean                  │
│  + markComplete(): void                     │
│  + toString()   : String  → "[✓] title"     │
└─────────────────────────────────────────────┘

┌─────────────────────────────────────────────┐
│  TodoList                                   │
│  ─────────────────────────────────────────  │
│  - tasks : ArrayList<Task>  (private)       │
│  ─────────────────────────────────────────  │
│  + addTask(title)       : void              │
│  + displayAll()         : void              │
│  + markComplete(index)  : void              │
│  + deleteTask(index)    : void              │
│  + showPending()        : void              │
│  + showCompleted()      : void              │
└─────────────────────────────────────────────┘

┌─────────────────────────────────────────────┐
│  Main                                       │
│  ─────────────────────────────────────────  │
│  + main(args) → menu loop + Scanner input   │
└─────────────────────────────────────────────┘

ArrayList vs Array

	Array	ArrayList
Size	Fixed at declaration	Grows/shrinks dynamically
Deletion	Manual shift required	remove(index) handles it
Syntax	tasks[i]	tasks.get(i)

This project uses ArrayList<Task> so there is no hard limit on the number of tasks.

Deletion — How ArrayList.remove() Works

When a task at index i is deleted, Java shifts all elements after it one position left automatically.

Before delete at index 1:  ["Buy milk", "Call doctor", "Study Java"]
After  delete at index 1:  ["Buy milk", "Study Java"]

No manual shifting needed — unlike C arrays where you write the shift loop yourself.

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Getting Started

Prerequisites

• JDK 8 or higher installed

Check with:

java -version

Compile

javac Main.java

Run

java Main

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Usage

After running, you will see:

================================
      TO-DO LIST APPLICATION
================================

--- MENU ---
1. Add Task
2. View All Tasks
3. Mark Task as Complete
4. Delete Task
5. View Pending Tasks
6. View Completed Tasks
7. Exit
Enter your choice:

Enter a number from 1 to 7 and follow the prompts.

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Sample Output

Adding Tasks

Enter your choice: 1
Enter task title: Complete Java assignment
Task added: "Complete Java assignment"

Enter your choice: 1
Enter task title: Buy groceries
Task added: "Buy groceries"

View All

--- TO-DO LIST ---
1. [ ] Complete Java assignment
2. [ ] Buy groceries
Total tasks: 2

Mark Complete

Enter task number to mark complete: 1
Task marked complete: "Complete Java assignment"

View All After Marking

--- TO-DO LIST ---
1. [✓] Complete Java assignment
2. [ ] Buy groceries
Total tasks: 2

View Pending Only

--- PENDING TASKS ---
2. [ ] Buy groceries

Delete

Enter task number to delete: 2
Deleted: "Buy groceries"

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Limitations

Limitation	Details
No persistence	Tasks are stored in memory only; lost when the program exits
No edit	To rename a task, delete it and add a new one
Single user	No multi-user or session support

To add persistence, tasks can be written to and read from a .txt or .csv file using FileWriter and BufferedReader — a straightforward next step.