CODESAMPLE

Snapshot - Java

Snapshot Java

The Snapshot pattern captures the internal state of an object at a certain point in time, allowing it to be restored later. This is useful for implementing features like undo/redo, transaction rollback, or saving game states. The code defines a Snapshot class holding the object’s state and an Originator class that creates snapshots and restores from them. The Caretaker simply stores snapshots without knowing the Originator’s internals. This implementation uses simple getters and setters for state, making it straightforward and readable, fitting Java’s object-oriented style. Immutability of the Snapshot class is also a good practice.

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

// Originator
class TextEditor {
    private String text;

    public TextEditor(String initialText) {
        this.text = initialText;
    }

    public String getText() {
        return text;
    }

    public void setText(String text) {
        this.text = text;
    }

    public Snapshot createSnapshot() {
        return new Snapshot(this.text);
    }

    public void restore(Snapshot snapshot) {
        this.text = snapshot.getText();
    }
}

// Snapshot
class Snapshot {
    private final String text;

    public Snapshot(String text) {
        this.text = text;
    }

    public String getText() {
        return text;
    }
}

// Caretaker
class History {
    private List<Snapshot> snapshots = new ArrayList<>();

    public void addSnapshot(Snapshot snapshot) {
        snapshots.add(snapshot);
    }

    public Snapshot getSnapshot(int index) {
        if (index >= 0 && index < snapshots.size()) {
            return snapshots.get(index);
        }
        return null; // Or throw an exception
    }
}

// Example Usage
public class Main {
    public static void main(String[] args) {
        TextEditor editor = new TextEditor("Initial text.");
        History history = new History();

        history.addSnapshot(editor.createSnapshot()); // Save initial state

        editor.setText("More text added.");
        history.addSnapshot(editor.createSnapshot()); // Save after addition

        System.out.println("Current text: " + editor.getText());

        Snapshot snapshot = history.getSnapshot(0);
        if (snapshot != null) {
            editor.restore(snapshot);
            System.out.println("Restored text: " + editor.getText());
        }
    }
}