备忘录(Memento)模式
2022/1/11 23:35:29
本文主要是介绍备忘录(Memento)模式,对大家解决编程问题具有一定的参考价值,需要的程序猿们随着小编来一起学习吧!
备忘录(Memento)
Intent
在不违反封装的情况下获得对象的内部状态,从而在需要时可以将对象恢复到最初状态。
Class Diagram
- Originator:原始对象
- Caretaker:负责保存好备忘录
- Memento:备忘录,存储原始对象的状态。备忘录实际上有两个接口,一个是提供给 Caretaker 的窄接口:它只能将备忘录传递给其它对象;一个是提供给 Originator 的宽接口,允许它访问到先前状态所需的所有数据。理想情况是只允许 Originator 访问本备忘录的内部状态。
Implementation
以下实现了一个简单计算器程序,可以输入两个值,然后计算这两个值的和。备忘录模式允许将这两个值存储起来,然后在某个时刻用存储的状态进行恢复。
实现参考:Memento Pattern - Calculator Example - Java Sourcecode
/** * Originator Interface */ public interface Calculator { // Create Memento PreviousCalculationToCareTaker backupLastCalculation(); // setMemento void restorePreviousCalculation(PreviousCalculationToCareTaker memento); int getCalculationResult(); void setFirstNumber(int firstNumber); void setSecondNumber(int secondNumber); }
/** * Originator Implementation */ public class CalculatorImp implements Calculator { private int firstNumber; private int secondNumber; @Override public PreviousCalculationToCareTaker backupLastCalculation() { // create a memento object used for restoring two numbers return new PreviousCalculationImp(firstNumber, secondNumber); } @Override public void restorePreviousCalculation(PreviousCalculationToCareTaker memento) { this.firstNumber = ((PreviousCalculationToOriginator) memento).getFirstNumber(); this.secondNumber = ((PreviousCalculationToOriginator) memento).getSecondNumber(); } @Override public int getCalculationResult() { // result is adding two numbers return firstNumber + secondNumber; } @Override public void setFirstNumber(int firstNumber) { this.firstNumber = firstNumber; } @Override public void setSecondNumber(int secondNumber) { this.secondNumber = secondNumber; } }
/** * Memento Interface to Originator * * This interface allows the originator to restore its state */ public interface PreviousCalculationToOriginator { int getFirstNumber(); int getSecondNumber(); }
/** * Memento interface to CalculatorOperator (Caretaker) */ public interface PreviousCalculationToCareTaker { // no operations permitted for the caretaker }
/** * Memento Object Implementation * <p> * Note that this object implements both interfaces to Originator and CareTaker */ public class PreviousCalculationImp implements PreviousCalculationToCareTaker, PreviousCalculationToOriginator { private int firstNumber; private int secondNumber; public PreviousCalculationImp(int firstNumber, int secondNumber) { this.firstNumber = firstNumber; this.secondNumber = secondNumber; } @Override public int getFirstNumber() { return firstNumber; } @Override public int getSecondNumber() { return secondNumber; } }
/** * CareTaker object */ public class Client { public static void main(String[] args) { // program starts Calculator calculator = new CalculatorImp(); // assume user enters two numbers calculator.setFirstNumber(10); calculator.setSecondNumber(100); // find result System.out.println(calculator.getCalculationResult()); // Store result of this calculation in case of error PreviousCalculationToCareTaker memento = calculator.backupLastCalculation(); // user enters a number calculator.setFirstNumber(17); // user enters a wrong second number and calculates result calculator.setSecondNumber(-290); // calculate result System.out.println(calculator.getCalculationResult()); // user hits CTRL + Z to undo last operation and see last result calculator.restorePreviousCalculation(memento); // result restored System.out.println(calculator.getCalculationResult()); } }
110 -273 110
JDK
- java.io.Serializable
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