应用场景也比较明确和有限,主要是用来防丢失、撤销、恢复等。
备忘录模式的原理与实现
备忘录模式,也叫快照(Snapshot)模式,英文翻译是 Memento Design Pattern。
在不违背封装原则的前提下,捕获一个对象的内部状态,并在该对象之外保存这个状态,以便之后恢复对象为先前的状态。
利用栈:
public class InputText {
private StringBuilder text = new StringBuilder();
public String getText() {
return text.toString();
}
public void append(String input) {
text.append(input);
}
public Snapshot createSnapshot() {
return new Snapshot(text.toString());
}
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 snapshotsHolder = 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 = snapshotsHolder.popSnapshot();
inputText.restoreSnapshot(snapshot);
} else {
snapshotsHolder.pushSnapshot(inputText.createSnapshot());
inputText.append(input);
}
}
}
}
如何优化内存和时间消耗?
低频率全量备份”和“高频率增量备份”相结合的方法。