java设计模式之备忘录

public class InputText {
    private StringBuilder text = new StringBuilder();
    
    public Snapshot createSnapshot() {
        return new Snapshot(text.toString());
    }

    public void append(String input) {
        text.append(input);
    }

    public void restoreSnapshot(Snapshot snapshot) {
        this.text.replace(0, this.text.length(), snapshot.getText());
    }
    
}

public class Snapshot {
    private String text;

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

    public String getText() {
        return this.text;
    }
}

public class SnapshotHolder {
    private Stack<Snapshot> snapshots = new Stack<>();

    public Snapshot popSnapshot() {
        return snapshots.pop();
    }

    public void pushSnapshot(Snapshot snapshot){
        snapshots.push(snapshot);
    }
}

public class ApplicationMain {
    public static void main(String[] args) {
        InputText inputText = new InputText();
        SnapshotHolder snapshotHolder = new SnapshotHolder();
        ScAnner scAnner = new ScAnner(System.in);
        while (scAnner.hasNext()){
            String input = scAnner.next();
            if(input.equals(":list")){
                System.out.println(inputText.toString());
            }else if(input.equals(":undo")){
                Snapshot snapshot = snapshotHolder.popSnapshot();
                inputText.restoreSnapshot(snapshot);
            }else{
                snapshotHolder.pushSnapshot(inputText.createSnapshot());
                inputText.append(input);
            }
        }
    }
}

>Hello
>:list
Hello
>world
>:list
Helloworld
>:undo
>:list
Hello