Merge pull request #7423 from dupirefr/bael-3090

dupirefr/dupire.francois+pro@gmail.com [BAEL-3090] Memento Design Pattern

patterns/design-patterns-2/pom.xml

@@ -30,6 +30,12 @@
             <groupId>org.apache.commons</groupId>
             <artifactId>commons-lang3</artifactId>
             <version>${commons-lang3.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
         </dependency>
    		<dependency>
             <groupId>org.inferred</groupId>
@@ -49,6 +55,7 @@
         <maven.compiler.source>1.8</maven.compiler.source>
         <maven.compiler.target>1.8</maven.compiler.target>
         <intellij.annotations.version>16.0.2</intellij.annotations.version>
+        <assertj.version>3.12.2</assertj.version>
         <freebuilder.version>2.4.1</freebuilder.version>
         <javax.annotations.version>3.0.2</javax.annotations.version>
     </properties>

patterns/design-patterns-2/src/main/java/com/baeldung/memento/TextEditor.java

@@ -0,0 +1,27 @@
+package com.baeldung.memento;
+
+public class TextEditor {
+
+    private TextWindow textWindow;
+    private TextWindowState savedTextWindow;
+
+    public TextEditor(TextWindow textWindow) {
+        this.textWindow = textWindow;
+    }
+
+    public void write(String text) {
+        textWindow.addText(text);
+    }
+
+    public String print() {
+        return textWindow.getCurrentText();
+    }
+
+    public void hitSave() {
+        savedTextWindow = textWindow.save();
+    }
+
+    public void hitUndo() {
+        textWindow.restore(savedTextWindow);
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/memento/TextWindow.java

@@ -0,0 +1,26 @@
+package com.baeldung.memento;
+
+public class TextWindow {
+
+    private StringBuilder currentText;
+
+    public TextWindow() {
+        this.currentText = new StringBuilder();
+    }
+
+    public String getCurrentText() {
+        return currentText.toString();
+    }
+
+    public void addText(String text) {
+        currentText.append(text);
+    }
+
+    public TextWindowState save() {
+        return new TextWindowState(currentText.toString());
+    }
+
+    public void restore(TextWindowState save) {
+        currentText = new StringBuilder(save.getText());
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/memento/TextWindowState.java

@@ -0,0 +1,14 @@
+package com.baeldung.memento;
+
+public class TextWindowState {
+
+    private String text;
+
+    public TextWindowState(String text) {
+        this.text = text;
+    }
+
+    public String getText() {
+        return text;
+    }
+}

patterns/design-patterns-2/src/test/java/com/baeldung/memento/TextEditorUnitTest.java

@@ -0,0 +1,20 @@
+package com.baeldung.memento;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class TextEditorUnitTest {
+
+    @Test
+    void givenTextEditor_whenAddTextSaveAddMoreAndUndo_thenSavecStateRestored() {
+        TextEditor textEditor = new TextEditor(new TextWindow());
+        textEditor.write("The Memento Design Pattern\n");
+        textEditor.write("How to implement it in Java?\n");
+        textEditor.hitSave();
+        textEditor.write("Buy milk and eggs before coming home\n");
+        textEditor.hitUndo();
+
+        assertThat(textEditor.print()).isEqualTo("The Memento Design Pattern\nHow to implement it in Java?\n");
+    }
+}