BAEL-16653 (#7691)

* added module 'design-patterns-behavioral'

* added module 'design-patterns-structural'

* added module 'design-patterns-creational'

* added module 'design-patterns-architectural'

* added module 'design-patterns-functional'

* moved facade code examples from design-patterns to design-patterns-structural

* moved singleton examples from design-patterns to design-patterns-creational

* moved bridge examples from design-patterns to design-patterns-structural

* moved creational examples from design-patterns to design-patterns-creational

* moved observer examples from design-patterns to design-patterns-behavioral

* moved flyweight examples from design-patterns to design-patterns-creational

* moved service locator examples from design-patterns to design-patterns-architectural

* moved double checked locking singleton examples from design-patterns to design-patterns-creational

* moved composite examples from design-patterns to design-patterns-structural

* moved visitor examples from design-patterns to design-patterns-behavioral

* moved dao examples from design-patterns to design-patterns-architectural

* moved interpreter examples from design-patterns to design-patterns-behavioral

* moved state examples from design-patterns to design-patterns-behavioral

* moved decorator examples from design-patterns to design-patterns-structural

* renamed LogerUtil to LoggerUtil

* moved template method examples from design-patterns to design-patterns-behavioral

* moved chain of responsibility examples from design-patterns to design-patterns-behavioral

* moved command examples from design-patterns to design-patterns-behavioral

* moved constructor vs static factory method examples from design-patterns to design-patterns-creational

* moved adapter examples from design-patterns to design-patterns-structural

* moved currying examples from design-patterns to design-patterns-functional

* moved proxy examples from design-patterns to design-patterns-structural

* moved persistence.xml from design-patterns to design-patterns-architectural

* deleted empty module: design-patterns

* moved mediator examples from design-patterns-2 to design-patterns-behavioral

* moved null object examples from design-patterns-2 to design-patterns-behavioral

* moved null check examples from design-patterns to design-patterns-behavioral

* moved freebuilder examples from design-patterns-2 to design-patterns-creational

* added module design-patterns-behavioral-2

* moved memento examples from design-patterns-2 to design-patterns-behavioral-2

* removed empty module design-patterns-2

* changed http to https in readmes in modules design-patterns-*

patterns/design-patterns-behavioral-2/README.md

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+### Relevant Articles:
+- [Memento Design Pattern in Java](https://www.baeldung.com/java-memento-design-pattern)

patterns/design-patterns-behavioral-2/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>design-patterns-behavioral-2</artifactId>
+    <version>1.0</version>
+    <name>design-patterns-behavioral-2</name>
+	<packaging>jar</packaging>
+	
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>patterns</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+        <relativePath>..</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+	
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <maven.compiler.source>1.8</maven.compiler.source>
+        <maven.compiler.target>1.8</maven.compiler.target>
+        
+        <assertj.version>3.12.2</assertj.version>
+    </properties>
+</project>

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

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+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-behavioral-2/src/main/java/com/baeldung/memento/TextWindow.java

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+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-behavioral-2/src/main/java/com/baeldung/memento/TextWindowState.java

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+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-behavioral-2/src/test/java/com/baeldung/memento/TextEditorUnitTest.java

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+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");
+    }
+}