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notes/设计模式.md

@@ -1204,9 +1204,176 @@ doSprinkler()
 
 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。
 
+### 类图
+
+- Originator：原始对象
+- Caretaker：负责保存好备忘录
+- Menento：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。
+
+<div align="center"> <img src="../pics//867e93eb-3161-4f39-b2d2-c0cd3788e194.png"/> </div><br>
+
+### 实现
+
+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](https://www.oodesign.com/memento-pattern-calculator-example-java-sourcecode.html)
+
+```java
+/**
+ * Originator Interface
+ */
+public interface Calculator {
+
+    // Create Memento
+    PreviousCalculationToCareTaker backupLastCalculation();
+
+    // setMemento
+    void restorePreviousCalculation(PreviousCalculationToCareTaker memento);
+
+    int getCalculationResult();
+
+    void setFirstNumber(int firstNumber);
+
+    void setSecondNumber(int secondNumber);
+}
+```
+
+```java
+/**
+ * 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;
+    }
+}
+```
+
+```java
+/**
+ * Memento Interface to Originator
+ * 
+ * This interface allows the originator to restore its state
+ */
+public interface PreviousCalculationToOriginator {
+    int getFirstNumber();
+    int getSecondNumber();
+}
+```
+
+```java
+/**
+ *  Memento interface to CalculatorOperator (Caretaker)
+ */
+public interface PreviousCalculationToCareTaker {
+    // no operations permitted for the caretaker
+}
+```
+
+```java
+/**
+ * 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;
+    }
+}
+```
+
+```java
+/**
+ * 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());
+    }
+}
+```
+
+```html
+110
+-273
+110
+```
+
 ### JDK
 
-- [java.util.Date](http://docs.oracle.com/javase/8/docs/api/java/util/Date.html)
+- java.io.Serializable
 
 ## 7. 观察者（Observer）