Add memento design pattern with test scenario (#57)

Author: mperor

DesignPatterns/README.md

@@ -12,6 +12,7 @@ with practical examples and best practices for using design patterns to create r
 - [Chain of Responsibility](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/chain/of/responsibility) 🔗
 - [Command](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/command) 📝
 - [Execute Around Method (EAM)](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/eam) ⭕
+- [Memento](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/memento) 💾
 - [Observer](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/observer) 👀
 - [State](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/state) 📜
 - [Strategy](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/strategy) 🎯

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/memento/History.java

@@ -0,0 +1,19 @@
+package pl.mperor.lab.java.design.pattern.behavioral.memento;
+
+import java.util.ArrayDeque;
+import java.util.Deque;
+
+class History {
+
+ private final Deque<TextMemento> history = new ArrayDeque<>();
+
+ void save(TextEditor editor) {
+ history.push(editor.save());
+ }
+
+ void undo(TextEditor editor) {
+ if (!history.isEmpty()) {
+ editor.restore(history.pop());
+ }
+ }
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/memento/TextEditor.java

@@ -0,0 +1,23 @@
+package pl.mperor.lab.java.design.pattern.behavioral.memento;
+
+class TextEditor {
+
+ private StringBuilder content = new StringBuilder();
+
+ TextEditor write(String text) {
+ content.append(text);
+ return this;
+ }
+
+ TextMemento save() {
+ return new TextMemento(content.toString());
+ }
+
+ void restore(TextMemento memento) {
+ content = new StringBuilder(memento.content());
+ }
+
+ String getContent() {
+ return content.toString();
+ }
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/memento/TextMemento.java

@@ -0,0 +1,4 @@
+package pl.mperor.lab.java.design.pattern.behavioral.memento;
+
+record TextMemento(String content) {
+}

DesignPatterns/src/test/java/pl/mperor/lab/java/design/pattern/behavioral/memento/TextEditorMementoTest.java

@@ -0,0 +1,23 @@
+package pl.mperor.lab.java.design.pattern.behavioral.memento;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class TextEditorMementoTest {
+
+ @Test
+ public void testSavingAndRestoringWithTextMemento() {
+ var editor = new TextEditor();
+ var history = new History();
+
+ editor.write("⭐");
+ Assertions.assertEquals("⭐", editor.getContent());
+ history.save(editor);
+
+ editor.write("1️⃣").write("2️⃣").write("3️⃣");
+ Assertions.assertEquals("⭐1️⃣2️⃣3️⃣", editor.getContent());
+
+ history.undo(editor);
+ Assertions.assertEquals("⭐", editor.getContent());
+ }
+}