Знімок на Java

Знімок — це поведінковий патерн, що дозволяє робити знімки внутрішнього стану об’єктів, а потім відновлювати їх.

При цьому Знімок не розкриває подробиць реалізації об’єктів і клієнт не має доступу до захищеної інформації об’єкта.

Складність:

Популярність:

Застосування: Знімок на Java найчастіше за все реалізовують за допомогою серіалізації. Але це не єдиний та не найефективніший метод збереження стану об’єктів під час виконання програми.

Приклади Знімка в стандартних бібліотеках Java:

Усі реалізації java.io.Serializable можуть бути використані як аналог Знімка.
Усі реалізації javax.faces.component.StateHolder

Скасування в редакторі фігур

В даному графічному редакторі ми можемо змінювати колір і позицію фігур. Користувач може скасовувати або повторювати дії, використовуючи гарячі клавіші.

Механізм скасування побудований за допомогою патерна Знімок і Команди. Перед виконанням команди, редактор зберігає в історії знімок свого стану. Якщо потрібно скасувати команду, редактор бере останній запис з історії та відновлює стан знімка. Для подальшої відміни береться попередня команда з історії.

Скасовані команди зберігаються в історії поки користувач не зробить яку-небудь дію. Це потрібно для того, щоби мати можливість повторювати скасовані команди.

editor

editor/Editor.java: Редактор

package refactoring_guru.memento.example.editor;

import refactoring_guru.memento.example.commands.Command;
import refactoring_guru.memento.example.history.History;
import refactoring_guru.memento.example.history.Memento;
import refactoring_guru.memento.example.shapes.CompoundShape;
import refactoring_guru.memento.example.shapes.Shape;

import javax.swing.*;
import java.io.*;
import java.util.Base64;

public class Editor extends JComponent {
    private Canvas canvas;
    private CompoundShape allShapes = new CompoundShape();
    private History history;

    public Editor() {
        canvas = new Canvas(this);
        history = new History();
    }

    public void loadShapes(Shape... shapes) {
        allShapes.clear();
        allShapes.add(shapes);
        canvas.refresh();
    }

    public CompoundShape getShapes() {
        return allShapes;
    }

    public void execute(Command c) {
        history.push(c, new Memento(this));
        c.execute();
    }

    public void undo() {
        if (history.undo())
            canvas.repaint();
    }

    public void redo() {
        if (history.redo())
            canvas.repaint();
    }

    public String backup() {
        try {
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            ObjectOutputStream oos = new ObjectOutputStream(baos);
            oos.writeObject(this.allShapes);
            oos.close();
            return Base64.getEncoder().encodeToString(baos.toByteArray());
        } catch (IOException e) {
            return "";
        }
    }

    public void restore(String state) {
        try {
            byte[] data = Base64.getDecoder().decode(state);
            ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(data));
            this.allShapes = (CompoundShape) ois.readObject();
            ois.close();
        } catch (ClassNotFoundException e) {
            System.out.print("ClassNotFoundException occurred.");
        } catch (IOException e) {
            System.out.print("IOException occurred.");
        }
    }
}

editor/Canvas.java: Полотно

package refactoring_guru.memento.example.editor;

import refactoring_guru.memento.example.commands.ColorCommand;
import refactoring_guru.memento.example.commands.MoveCommand;
import refactoring_guru.memento.example.shapes.Shape;

import javax.swing.*;
import javax.swing.border.Border;
import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;

class Canvas extends java.awt.Canvas {
    private Editor editor;
    private JFrame frame;
    private static final int PADDING = 10;

    Canvas(Editor editor) {
        this.editor = editor;
        createFrame();
        attachKeyboardListeners();
        attachMouseListeners();
        refresh();
    }

    private void createFrame() {
        frame = new JFrame();
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setLocationRelativeTo(null);

        JPanel contentPanel = new JPanel();
        Border padding = BorderFactory.createEmptyBorder(PADDING, PADDING, PADDING, PADDING);
        contentPanel.setBorder(padding);
        contentPanel.setLayout(new BoxLayout(contentPanel, BoxLayout.Y_AXIS));
        frame.setContentPane(contentPanel);

        contentPanel.add(new JLabel("Select and drag to move."), BorderLayout.PAGE_END);
        contentPanel.add(new JLabel("Right click to change color."), BorderLayout.PAGE_END);
        contentPanel.add(new JLabel("Undo: Ctrl+Z, Redo: Ctrl+R"), BorderLayout.PAGE_END);
        contentPanel.add(this);
        frame.setVisible(true);
        contentPanel.setBackground(Color.LIGHT_GRAY);
    }

    private void attachKeyboardListeners() {
        addKeyListener(new KeyAdapter() {
            @Override
            public void keyPressed(KeyEvent e) {
                if ((e.getModifiers() & KeyEvent.CTRL_MASK) != 0) {
                    switch (e.getKeyCode()) {
                        case KeyEvent.VK_Z:
                            editor.undo();
                            break;
                        case KeyEvent.VK_R:
                            editor.redo();
                            break;
                    }
                }
            }
        });
    }

    private void attachMouseListeners() {
        MouseAdapter colorizer = new MouseAdapter() {
            @Override
            public void mousePressed(MouseEvent e) {
                if (e.getButton() != MouseEvent.BUTTON3) {
                    return;
                }
                Shape target = editor.getShapes().getChildAt(e.getX(), e.getY());
                if (target != null) {
                    editor.execute(new ColorCommand(editor, new Color((int) (Math.random() * 0x1000000))));
                    repaint();
                }
            }
        };
        addMouseListener(colorizer);

        MouseAdapter selector = new MouseAdapter() {
            @Override
            public void mousePressed(MouseEvent e) {
                if (e.getButton() != MouseEvent.BUTTON1) {
                    return;
                }

                Shape target = editor.getShapes().getChildAt(e.getX(), e.getY());
                boolean ctrl = (e.getModifiers() & ActionEvent.CTRL_MASK) == ActionEvent.CTRL_MASK;

                if (target == null) {
                    if (!ctrl) {
                        editor.getShapes().unSelect();
                    }
                } else {
                    if (ctrl) {
                        if (target.isSelected()) {
                            target.unSelect();
                        } else {
                            target.select();
                        }
                    } else {
                        if (!target.isSelected()) {
                            editor.getShapes().unSelect();
                        }
                        target.select();
                    }
                }
                repaint();
            }
        };
        addMouseListener(selector);


        MouseAdapter dragger = new MouseAdapter() {
            MoveCommand moveCommand;

            @Override
            public void mouseDragged(MouseEvent e) {
                if ((e.getModifiersEx() & MouseEvent.BUTTON1_DOWN_MASK) != MouseEvent.BUTTON1_DOWN_MASK) {
                    return;
                }
                if (moveCommand == null) {
                    moveCommand = new MoveCommand(editor);
                    moveCommand.start(e.getX(), e.getY());
                }
                moveCommand.move(e.getX(), e.getY());
                repaint();
            }

            @Override
            public void mouseReleased(MouseEvent e) {
                if (e.getButton() != MouseEvent.BUTTON1 || moveCommand == null) {
                    return;
                }
                moveCommand.stop(e.getX(), e.getY());
                editor.execute(moveCommand);
                this.moveCommand = null;
                repaint();
            }
        };
        addMouseListener(dragger);
        addMouseMotionListener(dragger);
    }

    public int getWidth() {
        return editor.getShapes().getX() + editor.getShapes().getWidth() + PADDING;
    }

    public int getHeight() {
        return editor.getShapes().getY() + editor.getShapes().getHeight() + PADDING;
    }

    void refresh() {
        this.setSize(getWidth(), getHeight());
        frame.pack();
    }

    public void update(Graphics g) {
        paint(g);
    }

    public void paint(Graphics graphics) {
        BufferedImage buffer = new BufferedImage(this.getWidth(), this.getHeight(), BufferedImage.TYPE_INT_RGB);
        Graphics2D ig2 = buffer.createGraphics();
        ig2.setBackground(Color.WHITE);
        ig2.clearRect(0, 0, this.getWidth(), this.getHeight());

        editor.getShapes().paint(buffer.getGraphics());

        graphics.drawImage(buffer, 0, 0, null);
    }
}

history

history/History.java: Історія використовує знімки і команди

package refactoring_guru.memento.example.history;

import refactoring_guru.memento.example.commands.Command;

import java.util.ArrayList;
import java.util.List;

public class History {
    private List<Pair> history = new ArrayList<Pair>();
    private int virtualSize = 0;

    private class Pair {
        Command command;
        Memento memento;
        Pair(Command c, Memento m) {
            command = c;
            memento = m;
        }

        private Command getCommand() {
            return command;
        }

        private Memento getMemento() {
            return memento;
        }
    }

    public void push(Command c, Memento m) {
        if (virtualSize != history.size() && virtualSize > 0) {
            history = history.subList(0, virtualSize - 1);
        }
        history.add(new Pair(c, m));
        virtualSize = history.size();
    }

    public boolean undo() {
        Pair pair = getUndo();
        if (pair == null) {
            return false;
        }
        System.out.println("Undoing: " + pair.getCommand().getName());
        pair.getMemento().restore();
        return true;
    }

    public boolean redo() {
        Pair pair = getRedo();
        if (pair == null) {
            return false;
        }
        System.out.println("Redoing: " + pair.getCommand().getName());
        pair.getMemento().restore();
        pair.getCommand().execute();
        return true;
    }

    private Pair getUndo() {
        if (virtualSize == 0) {
            return null;
        }
        virtualSize = Math.max(0, virtualSize - 1);
        return history.get(virtualSize);
    }

    private Pair getRedo() {
        if (virtualSize == history.size()) {
            return null;
        }
        virtualSize = Math.min(history.size(), virtualSize + 1);
        return history.get(virtualSize - 1);
    }
}

history/Memento.java: Знімок

package refactoring_guru.memento.example.history;

import refactoring_guru.memento.example.editor.Editor;

public class Memento {
    private String backup;
    private Editor editor;

    public Memento(Editor editor) {
        this.editor = editor;
        this.backup = editor.backup();
    }

    public void restore() {
        editor.restore(backup);
    }
}

commands

commands/Command.java: Інтерфейс команд

package refactoring_guru.memento.example.commands;

public interface Command {
    String getName();
    void execute();
}

commands/ColorCommand.java: Команда зміни кольору

package refactoring_guru.memento.example.commands;

import refactoring_guru.memento.example.editor.Editor;
import refactoring_guru.memento.example.shapes.Shape;

import java.awt.*;

public class ColorCommand implements Command {
    private Editor editor;
    private Color color;

    public ColorCommand(Editor editor, Color color) {
        this.editor = editor;
        this.color = color;
    }

    @Override
    public String getName() {
        return "Colorize: " + color.toString();
    }

    @Override
    public void execute() {
        for (Shape child : editor.getShapes().getSelected()) {
            child.setColor(color);
        }
    }
}

commands/MoveCommand.java: Команда переміщення

package refactoring_guru.memento.example.commands;

import refactoring_guru.memento.example.editor.Editor;
import refactoring_guru.memento.example.shapes.Shape;

public class MoveCommand implements Command {
    private Editor editor;
    private int startX, startY;
    private int endX, endY;

    public MoveCommand(Editor editor) {
        this.editor = editor;
    }

    @Override
    public String getName() {
        return "Move by X:" + (endX - startX) + " Y:" + (endY - startY);
    }

    public void start(int x, int y) {
        startX = x;
        startY = y;
        for (Shape child : editor.getShapes().getSelected()) {
            child.drag();
        }
    }

    public void move(int x, int y) {
        for (Shape child : editor.getShapes().getSelected()) {
            child.moveTo(x - startX, y - startY);
        }
    }

    public void stop(int x, int y) {
        endX = x;
        endY = y;
        for (Shape child : editor.getShapes().getSelected()) {
            child.drop();
        }
    }

    @Override
    public void execute() {
        for (Shape child : editor.getShapes().getSelected()) {
            child.moveBy(endX - startX, endY - startY);
        }
    }
}

shapes: Різноманітні фігури

shapes/Shape.java

package refactoring_guru.memento.example.shapes;

import java.awt.*;
import java.io.Serializable;

public interface Shape extends Serializable {
    int getX();
    int getY();
    int getWidth();
    int getHeight();
    void drag();
    void drop();
    void moveTo(int x, int y);
    void moveBy(int x, int y);
    boolean isInsideBounds(int x, int y);
    Color getColor();
    void setColor(Color color);
    void select();
    void unSelect();
    boolean isSelected();
    void paint(Graphics graphics);
}

shapes/BaseShape.java

package refactoring_guru.memento.example.shapes;

import java.awt.*;

public abstract class BaseShape implements Shape {
    int x, y;
    private int dx = 0, dy = 0;
    private Color color;
    private boolean selected = false;

    BaseShape(int x, int y, Color color) {
        this.x = x;
        this.y = y;
        this.color = color;
    }

    @Override
    public int getX() {
        return x;
    }

    @Override
    public int getY() {
        return y;
    }

    @Override
    public int getWidth() {
        return 0;
    }

    @Override
    public int getHeight() {
        return 0;
    }

    @Override
    public void drag() {
        dx = x;
        dy = y;
    }

    @Override
    public void moveTo(int x, int y) {
        this.x = dx + x;
        this.y = dy + y;
    }

    @Override
    public void moveBy(int x, int y) {
        this.x += x;
        this.y += y;
    }

    @Override
    public void drop() {
        this.x = dx;
        this.y = dy;
    }

    @Override
    public boolean isInsideBounds(int x, int y) {
        return x > getX() && x < (getX() + getWidth()) &&
                y > getY() && y < (getY() + getHeight());
    }

    @Override
    public Color getColor() {
        return color;
    }

    @Override
    public void setColor(Color color) {
        this.color = color;
    }

    @Override
    public void select() {
        selected = true;
    }

    @Override
    public void unSelect() {
        selected = false;
    }

    @Override
    public boolean isSelected() {
        return selected;
    }

    void enableSelectionStyle(Graphics graphics) {
        graphics.setColor(Color.LIGHT_GRAY);

        Graphics2D g2 = (Graphics2D) graphics;
        float[] dash1 = {2.0f};
        g2.setStroke(new BasicStroke(1.0f,
                BasicStroke.CAP_BUTT,
                BasicStroke.JOIN_MITER,
                2.0f, dash1, 0.0f));
    }

    void disableSelectionStyle(Graphics graphics) {
        graphics.setColor(color);
        Graphics2D g2 = (Graphics2D) graphics;
        g2.setStroke(new BasicStroke());
    }

    @Override
    public void paint(Graphics graphics) {
        if (isSelected()) {
            enableSelectionStyle(graphics);
        }
        else {
            disableSelectionStyle(graphics);
        }

        // ...
    }
}

shapes/Circle.java

package refactoring_guru.memento.example.shapes;

import java.awt.*;

public class Circle extends BaseShape {
    private int radius;

    public Circle(int x, int y, int radius, Color color) {
        super(x, y, color);
        this.radius = radius;
    }

    @Override
    public int getWidth() {
        return radius * 2;
    }

    @Override
    public int getHeight() {
        return radius * 2;
    }

    @Override
    public void paint(Graphics graphics) {
        super.paint(graphics);
        graphics.drawOval(x, y, getWidth() - 1, getHeight() - 1);
    }
}

shapes/Dot.java

package refactoring_guru.memento.example.shapes;

import java.awt.*;

public class Dot extends BaseShape {
    private final int DOT_SIZE = 3;

    public Dot(int x, int y, Color color) {
        super(x, y, color);
    }

    @Override
    public int getWidth() {
        return DOT_SIZE;
    }

    @Override
    public int getHeight() {
        return DOT_SIZE;
    }

    @Override
    public void paint(Graphics graphics) {
        super.paint(graphics);
        graphics.fillRect(x - 1, y - 1, getWidth(), getHeight());
    }
}

shapes/Rectangle.java

package refactoring_guru.memento.example.shapes;

import java.awt.*;

public class Rectangle extends BaseShape {
    private int width;
    private int height;

    public Rectangle(int x, int y, int width, int height, Color color) {
        super(x, y, color);
        this.width = width;
        this.height = height;
    }

    @Override
    public int getWidth() {
        return width;
    }

    @Override
    public int getHeight() {
        return height;
    }

    @Override
    public void paint(Graphics graphics) {
        super.paint(graphics);
        graphics.drawRect(x, y, getWidth() - 1, getHeight() - 1);
    }
}

shapes/CompoundShape.java

package refactoring_guru.memento.example.shapes;

import java.awt.*;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class CompoundShape extends BaseShape {
    private List<Shape> children = new ArrayList<>();

    public CompoundShape(Shape... components) {
        super(0, 0, Color.BLACK);
        add(components);
    }

    public void add(Shape component) {
        children.add(component);
    }

    public void add(Shape... components) {
        children.addAll(Arrays.asList(components));
    }

    public void remove(Shape child) {
        children.remove(child);
    }

    public void remove(Shape... components) {
        children.removeAll(Arrays.asList(components));
    }

    public void clear() {
        children.clear();
    }

    @Override
    public int getX() {
        if (children.size() == 0) {
            return 0;
        }
        int x = children.get(0).getX();
        for (Shape child : children) {
            if (child.getX() < x) {
                x = child.getX();
            }
        }
        return x;
    }

    @Override
    public int getY() {
        if (children.size() == 0) {
            return 0;
        }
        int y = children.get(0).getY();
        for (Shape child : children) {
            if (child.getY() < y) {
                y = child.getY();
            }
        }
        return y;
    }

    @Override
    public int getWidth() {
        int maxWidth = 0;
        int x = getX();
        for (Shape child : children) {
            int childsRelativeX = child.getX() - x;
            int childWidth = childsRelativeX + child.getWidth();
            if (childWidth > maxWidth) {
                maxWidth = childWidth;
            }
        }
        return maxWidth;
    }

    @Override
    public int getHeight() {
        int maxHeight = 0;
        int y = getY();
        for (Shape child : children) {
            int childsRelativeY = child.getY() - y;
            int childHeight = childsRelativeY + child.getHeight();
            if (childHeight > maxHeight) {
                maxHeight = childHeight;
            }
        }
        return maxHeight;
    }

    @Override
    public void drag() {
        for (Shape child : children) {
            child.drag();
        }
    }

    @Override
    public void drop() {
        for (Shape child : children) {
            child.drop();
        }
    }

    @Override
    public void moveTo(int x, int y) {
        for (Shape child : children) {
            child.moveTo(x, y);
        }
    }

    @Override
    public void moveBy(int x, int y) {
        for (Shape child : children) {
            child.moveBy(x, y);
        }
    }

    @Override
    public boolean isInsideBounds(int x, int y) {
        for (Shape child : children) {
            if (child.isInsideBounds(x, y)) {
                return true;
            }
        }
        return false;
    }

    @Override
    public void setColor(Color color) {
        super.setColor(color);
        for (Shape child : children) {
            child.setColor(color);
        }
    }

    @Override
    public void unSelect() {
        super.unSelect();
        for (Shape child : children) {
            child.unSelect();
        }
    }

    public Shape getChildAt(int x, int y) {
        for (Shape child : children) {
            if (child.isInsideBounds(x, y)) {
                return child;
            }
        }
        return null;
    }

    public boolean selectChildAt(int x, int y) {
        Shape child = getChildAt(x,y);
        if (child != null) {
            child.select();
            return true;
        }
        return false;
    }

    public List<Shape> getSelected() {
        List<Shape> selected = new ArrayList<>();
        for (Shape child : children) {
            if (child.isSelected()) {
                selected.add(child);
            }
        }
        return selected;
    }

    @Override
    public void paint(Graphics graphics) {
        if (isSelected()) {
            enableSelectionStyle(graphics);
            graphics.drawRect(getX() - 1, getY() - 1, getWidth() + 1, getHeight() + 1);
            disableSelectionStyle(graphics);
        }

        for (Shape child : children) {
            child.paint(graphics);
        }
    }
}

Demo.java: Клієнтський код

package refactoring_guru.memento.example;

import refactoring_guru.memento.example.editor.Editor;
import refactoring_guru.memento.example.shapes.Circle;
import refactoring_guru.memento.example.shapes.CompoundShape;
import refactoring_guru.memento.example.shapes.Dot;
import refactoring_guru.memento.example.shapes.Rectangle;

import java.awt.*;

public class Demo {
    public static void main(String[] args) {
        Editor editor = new Editor();
        editor.loadShapes(
                new Circle(10, 10, 10, Color.BLUE),

                new CompoundShape(
                        new Circle(110, 110, 50, Color.RED),
                        new Dot(160, 160, Color.RED)
                ),

                new CompoundShape(
                        new Rectangle(250, 250, 100, 100, Color.GREEN),
                        new Dot(240, 240, Color.GREEN),
                        new Dot(240, 360, Color.GREEN),
                        new Dot(360, 360, Color.GREEN),
                        new Dot(360, 240, Color.GREEN)
                )
        );
    }
}