ToDoApp.java

import javax.swing.*;
import javax.swing.border.EmptyBorder;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

/**
 * ToDoApp is a Java Swing-based desktop application that provides
 * a clean and user-friendly interface to manage a To-Do list.
 * Users can enter tasks into a text field, add them to the list,
 * select any task, and delete it.
 * 
 * Features:
 * - Clean, modern, responsive desktop GUI layout.
 * - System Look and Feel support for native window elements.
 * - Add/Delete task actions with validation dialogs.
 * - ActionListeners bound to both buttons and keyboard events (Enter key).
 * - Dynamic list rendering with alternating row colors (zebra striping).
 * - Real-time task count status indicator.
 * 
 * Suitable as a Java developer internship assignment.
 * 
 * Author: Mummana Devi Prasad
 */
public class ToDoApp {

    // Main window container
    private JFrame frame;
    // Input field for writing new task items
    private JTextField taskField;
    // List component showing all task items
    private JList<String> taskList;
    // Underlying data model that allows adding/removing list elements dynamically
    private DefaultListModel<String> listModel;
    // Interactive buttons for user operations
    private JButton addButton;
    private JButton deleteButton;
    // Label display showing total count of current tasks
    private JLabel statusLabel;

    /**
     * Constructor for ToDoApp. Initializes components and constructs the GUI.
     */
    public ToDoApp() {
        createAndShowGUI();
    }

    /**
     * Builds, styles, and displays the main user interface.
     */
    private void createAndShowGUI() {
        // Try to apply system's native look and feel for a cleaner, modern interface
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (Exception e) {
            // Fallback to cross-platform Look & Feel if system-specific L&F fails
            System.err.println("Native Look & Feel could not be set. Using default. Error: " + e.getMessage());
        }

        // Initialize the main window JFrame
        frame = new JFrame("Task Planner - My To-Do List");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(450, 520);
        frame.setMinimumSize(new Dimension(350, 400)); // Enforce minimum window size for responsiveness
        frame.setLocationRelativeTo(null); // Centers window on user's screen

        // Create main layout panel with spacious padding
        JPanel mainPanel = new JPanel(new BorderLayout(15, 15));
        mainPanel.setBorder(new EmptyBorder(20, 20, 20, 20));
        mainPanel.setBackground(new Color(245, 247, 250)); // Modern light-blue-gray background
        frame.setContentPane(mainPanel);

        // --- 1. HEADER PANEL ---
        // Contains application title and quick description
        JPanel headerPanel = new JPanel();
        headerPanel.setLayout(new BoxLayout(headerPanel, BoxLayout.Y_AXIS));
        headerPanel.setBackground(new Color(245, 247, 250));
        
        JLabel titleLabel = new JLabel("My Tasks");
        titleLabel.setFont(new Font("Segoe UI", Font.BOLD, 26));
        titleLabel.setForeground(new Color(31, 41, 55)); // Muted charcoal/dark text
        titleLabel.setAlignmentX(Component.LEFT_ALIGNMENT);

        JLabel subtitleLabel = new JLabel("Manage your daily activities and goals");
        subtitleLabel.setFont(new Font("Segoe UI", Font.PLAIN, 13));
        subtitleLabel.setForeground(new Color(107, 114, 128)); // Soft neutral gray
        subtitleLabel.setAlignmentX(Component.LEFT_ALIGNMENT);

        headerPanel.add(titleLabel);
        headerPanel.add(Box.createRigidArea(new Dimension(0, 4))); // Small spacer
        headerPanel.add(subtitleLabel);
        mainPanel.add(headerPanel, BorderLayout.NORTH);

        // --- 2. LIST PANEL (CENTER) ---
        // Dynamically displays tasks, utilizing a DefaultListModel to handle data changes.
        listModel = new DefaultListModel<>();
        
        // Add default tasks as starting suggestions/examples
        listModel.addElement("Finish the Java internship report");
        listModel.addElement("Read about Java Swing & Layout Managers");
        listModel.addElement("Review the MVC design pattern basics");

        taskList = new JList<>(listModel);
        taskList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        taskList.setFont(new Font("Segoe UI", Font.PLAIN, 14));
        taskList.setSelectionBackground(new Color(224, 231, 255)); // Indigo highlighted selection background
        taskList.setSelectionForeground(new Color(67, 56, 202));   // Deep indigo text for selected row

        // Custom Cell Renderer: Adds modern padding, separator lines, and alternating row colors (zebra striping)
        taskList.setCellRenderer(new DefaultListCellRenderer() {
            @Override
            public Component getListCellRendererComponent(JList<?> list, Object value, int index,
                                                          boolean isSelected, boolean cellHasFocus) {
                // Get standard label configuration
                JLabel label = (JLabel) super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);
                
                // Add inner text padding and a light gray bottom border to separate items
                label.setBorder(BorderFactory.createCompoundBorder(
                        BorderFactory.createMatteBorder(0, 0, 1, 0, new Color(243, 244, 246)),
                        BorderFactory.createEmptyBorder(12, 15, 12, 15)
                ));

                // Zebra striping color logic when the item is NOT selected
                if (!isSelected) {
                    label.setBackground(index % 2 == 0 ? Color.WHITE : new Color(250, 250, 250));
                    label.setForeground(new Color(55, 65, 81));
                }
                return label;
            }
        });

        // JScrollPane is required to support lists that exceed the initial window height
        JScrollPane scrollPane = new JScrollPane(taskList);
        scrollPane.setBorder(BorderFactory.createLineBorder(new Color(229, 231, 235), 1));
        scrollPane.getViewport().setBackground(Color.WHITE);
        mainPanel.add(scrollPane, BorderLayout.CENTER);

        // --- 3. INPUT AND CONTROL PANEL (SOUTH) ---
        // Holds task entry field, operational action buttons, and status label.
        JPanel southPanel = new JPanel();
        southPanel.setLayout(new BoxLayout(southPanel, BoxLayout.Y_AXIS));
        southPanel.setBackground(new Color(245, 247, 250));

        // Sub-panel for text input
        JPanel inputPanel = new JPanel(new BorderLayout(10, 10));
        inputPanel.setBackground(new Color(245, 247, 250));

        taskField = new JTextField();
        taskField.setFont(new Font("Segoe UI", Font.PLAIN, 14));
        taskField.setToolTipText("Enter task description here");
        // Modern input styling with comfortable margin/padding
        taskField.setBorder(BorderFactory.createCompoundBorder(
                BorderFactory.createLineBorder(new Color(209, 213, 219), 1),
                BorderFactory.createEmptyBorder(10, 12, 10, 12)
        ));

        inputPanel.add(taskField, BorderLayout.CENTER);
        southPanel.add(inputPanel);
        southPanel.add(Box.createRigidArea(new Dimension(0, 12))); // Vertical gap

        // Action Buttons Row: Grid layout ensures buttons have uniform sizes
        JPanel buttonPanel = new JPanel(new GridLayout(1, 2, 15, 0));
        buttonPanel.setBackground(new Color(245, 247, 250));

        // Create and style "Add Task" button
        addButton = new JButton("Add Task");
        addButton.setFont(new Font("Segoe UI", Font.BOLD, 14));
        addButton.setBackground(new Color(79, 70, 229)); // Indigo blue theme
        addButton.setForeground(Color.WHITE);
        addButton.setFocusPainted(false);
        addButton.setBorder(BorderFactory.createEmptyBorder(12, 0, 12, 0));
        addButton.setCursor(new Cursor(Cursor.HAND_CURSOR));

        // Create and style "Delete Task" button
        deleteButton = new JButton("Delete Task");
        deleteButton.setFont(new Font("Segoe UI", Font.BOLD, 14));
        deleteButton.setBackground(new Color(239, 68, 68)); // Soft crimson red theme
        deleteButton.setForeground(Color.WHITE);
        deleteButton.setFocusPainted(false);
        deleteButton.setBorder(BorderFactory.createEmptyBorder(12, 0, 12, 0));
        deleteButton.setCursor(new Cursor(Cursor.HAND_CURSOR));

        buttonPanel.add(addButton);
        buttonPanel.add(deleteButton);
        southPanel.add(buttonPanel);
        southPanel.add(Box.createRigidArea(new Dimension(0, 12))); // Vertical gap

        // Status bar panel showing task counts
        JPanel statusPanel = new JPanel(new FlowLayout(FlowLayout.LEFT, 0, 0));
        statusPanel.setBackground(new Color(245, 247, 250));

        statusLabel = new JLabel("Total Tasks: " + listModel.getSize());
        statusLabel.setFont(new Font("Segoe UI", Font.ITALIC, 12));
        statusLabel.setForeground(new Color(156, 163, 175)); // Muted gray text
        statusPanel.add(statusLabel);
        
        southPanel.add(statusPanel);
        mainPanel.add(southPanel, BorderLayout.SOUTH);

        // --- 4. ACTION LISTENERS (EVENT HANDLING) ---

        // Shared action handler to add a new task item
        ActionListener addTaskListener = new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                addTask();
            }
        };

        // Add task when clicking the button OR pressing "Enter" inside the text field
        addButton.addActionListener(addTaskListener);
        taskField.addActionListener(addTaskListener);

        // Delete task action listener
        deleteButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                deleteTask();
            }
        });

        // Finally, make the window frame visible to user
        frame.setVisible(true);
    }

    /**
     * Retrieves the text from the input field, validates it, and adds it to the list model.
     */
    private void addTask() {
        String taskText = taskField.getText().trim();
        
        if (taskText.isEmpty()) {
            // Trigger warning dialog if field is blank
            JOptionPane.showMessageDialog(frame,
                    "Task content cannot be empty! Please type a description.",
                    "Input Warning",
                    JOptionPane.WARNING_MESSAGE);
        } else {
            // Append task to the dynamic list model
            listModel.addElement(taskText);
            // Reset input field and bring cursor focus back
            taskField.setText("");
            taskField.requestFocusInWindow();
            // Re-render task count status
            updateStatusLabel();
        }
    }

    /**
     * Determines the currently selected task and deletes it.
     */
    private void deleteTask() {
        int selectedIndex = taskList.getSelectedIndex();
        
        if (selectedIndex == -1) {
            // Trigger warning dialog if deletion was clicked without picking a target
            JOptionPane.showMessageDialog(frame,
                    "Please select a task from the list below to delete it.",
                    "Selection Warning",
                    JOptionPane.WARNING_MESSAGE);
        } else {
            // Remove selection index from the list model
            listModel.remove(selectedIndex);
            // Re-render task count status
            updateStatusLabel();
        }
    }

    /**
     * Calculates the list model size and updates the status label text.
     */
    private void updateStatusLabel() {
        statusLabel.setText("Total Tasks: " + listModel.getSize());
    }

    /**
     * Entry point of the program.
     */
    public static void main(String[] args) {
        // Safely schedule the GUI construction task on the Event Dispatch Thread (EDT)
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new ToDoApp();
            }
        });
    }
}