《一天聊一个设计模式》备忘录

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);
}

  

 

  
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/**
 * 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; }
}

  

 

  
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/**
 * Memento Interface to Originator
 *
 * This interface allows the originator to restore its state
 */
public interface PreviousCalculationToOriginator { int getFirstNumber(); int getSecondNumber();
}

  

 

  
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/**
 *  Memento interface to CalculatorOperator (Caretaker)
 */
public interface PreviousCalculationToCareTaker { // no operations permitted for the caretaker
}

  

 

  
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/**
 * 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; }
}

  

 

  
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/**
 * 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()); }
}

  

 

  
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110
-273
110

  

 

  
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JDK

• java.io.Serializable

文章来源: fantianzuo.blog.csdn.net，作者：兔老大RabbitMQ，版权归原作者所有，如需转载，请联系作者。

原文链接：fantianzuo.blog.csdn.net/article/details/114656191