From a4a8e1dc6cce17ed5ace6ddd41be3b0a42f03728 Mon Sep 17 00:00:00 2001
From: Denis <dev.szczukocki.denis@gmail.com>
Date: Sun, 27 May 2018 13:40:54 +0200
Subject: [PATCH] BAEL-1792 overview of visitor design pattern

---
 .../java/com/baeldung/visitor/Document.java   | 20 ++++++++++++++++
 .../java/com/baeldung/visitor/Element.java    | 12 ++++++++++
 .../com/baeldung/visitor/ElementVisitor.java  | 14 +++++++++++
 .../com/baeldung/visitor/JsonElement.java     | 12 ++++++++++
 .../java/com/baeldung/visitor/Visitor.java    |  8 +++++++
 .../com/baeldung/visitor/VisitorDemo.java     | 23 +++++++++++++++++++
 .../java/com/baeldung/visitor/XmlElement.java | 12 ++++++++++
 7 files changed, 101 insertions(+)
 create mode 100644 patterns/design-patterns/src/main/java/com/baeldung/visitor/Document.java
 create mode 100644 patterns/design-patterns/src/main/java/com/baeldung/visitor/Element.java
 create mode 100644 patterns/design-patterns/src/main/java/com/baeldung/visitor/ElementVisitor.java
 create mode 100644 patterns/design-patterns/src/main/java/com/baeldung/visitor/JsonElement.java
 create mode 100644 patterns/design-patterns/src/main/java/com/baeldung/visitor/Visitor.java
 create mode 100644 patterns/design-patterns/src/main/java/com/baeldung/visitor/VisitorDemo.java
 create mode 100644 patterns/design-patterns/src/main/java/com/baeldung/visitor/XmlElement.java

diff --git a/patterns/design-patterns/src/main/java/com/baeldung/visitor/Document.java b/patterns/design-patterns/src/main/java/com/baeldung/visitor/Document.java
new file mode 100644
index 0000000000..575146a8e0
--- /dev/null
+++ b/patterns/design-patterns/src/main/java/com/baeldung/visitor/Document.java
@@ -0,0 +1,20 @@
+package com.baeldung.visitor;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Document extends Element {
+
+    List<Element> elements = new ArrayList<>();
+
+    public Document(String uuid) {
+        super(uuid);
+    }
+
+    @Override
+    public void accept(Visitor v) {
+        for (Element e : this.elements) {
+            e.accept(v);
+        }
+    }
+}
\ No newline at end of file
diff --git a/patterns/design-patterns/src/main/java/com/baeldung/visitor/Element.java b/patterns/design-patterns/src/main/java/com/baeldung/visitor/Element.java
new file mode 100644
index 0000000000..70c96c99e1
--- /dev/null
+++ b/patterns/design-patterns/src/main/java/com/baeldung/visitor/Element.java
@@ -0,0 +1,12 @@
+package com.baeldung.visitor;
+
+public abstract class Element {
+
+    public String uuid;
+
+    public Element(String uuid) {
+        this.uuid = uuid;
+    }
+
+    public abstract void accept(Visitor v);
+}
\ No newline at end of file
diff --git a/patterns/design-patterns/src/main/java/com/baeldung/visitor/ElementVisitor.java b/patterns/design-patterns/src/main/java/com/baeldung/visitor/ElementVisitor.java
new file mode 100644
index 0000000000..f8af42d554
--- /dev/null
+++ b/patterns/design-patterns/src/main/java/com/baeldung/visitor/ElementVisitor.java
@@ -0,0 +1,14 @@
+package com.baeldung.visitor;
+
+public class ElementVisitor implements Visitor {
+
+    @Override
+    public void visit(XmlElement xe) {
+        System.out.println("processing xml element with uuid: " + xe.uuid);
+    }
+
+    @Override
+    public void visit(JsonElement je) {
+        System.out.println("processing json element with uuid: " + je.uuid);
+    }
+}
\ No newline at end of file
diff --git a/patterns/design-patterns/src/main/java/com/baeldung/visitor/JsonElement.java b/patterns/design-patterns/src/main/java/com/baeldung/visitor/JsonElement.java
new file mode 100644
index 0000000000..a65fe277f1
--- /dev/null
+++ b/patterns/design-patterns/src/main/java/com/baeldung/visitor/JsonElement.java
@@ -0,0 +1,12 @@
+package com.baeldung.visitor;
+
+public class JsonElement extends Element {
+
+    public JsonElement(String uuid) {
+        super(uuid);
+    }
+
+    public void accept(Visitor v) {
+        v.visit(this);
+    }
+}
\ No newline at end of file
diff --git a/patterns/design-patterns/src/main/java/com/baeldung/visitor/Visitor.java b/patterns/design-patterns/src/main/java/com/baeldung/visitor/Visitor.java
new file mode 100644
index 0000000000..1cd94911a3
--- /dev/null
+++ b/patterns/design-patterns/src/main/java/com/baeldung/visitor/Visitor.java
@@ -0,0 +1,8 @@
+package com.baeldung.visitor;
+
+public interface Visitor {
+
+    void visit(XmlElement xe);
+
+    void visit(JsonElement je);
+}
diff --git a/patterns/design-patterns/src/main/java/com/baeldung/visitor/VisitorDemo.java b/patterns/design-patterns/src/main/java/com/baeldung/visitor/VisitorDemo.java
new file mode 100644
index 0000000000..ee3436616a
--- /dev/null
+++ b/patterns/design-patterns/src/main/java/com/baeldung/visitor/VisitorDemo.java
@@ -0,0 +1,23 @@
+package com.baeldung.visitor;
+
+import java.util.UUID;
+
+public class VisitorDemo {
+
+    public static void main(String[] args) {
+
+        Visitor v = new ElementVisitor();
+
+        Document d = new Document(generateUuid());
+        d.elements.add(new JsonElement(generateUuid()));
+        d.elements.add(new JsonElement(generateUuid()));
+        d.elements.add(new XmlElement(generateUuid()));
+
+        d.accept(v);
+    }
+
+    private static String generateUuid() {
+        return UUID.randomUUID()
+            .toString();
+    }
+}
\ No newline at end of file
diff --git a/patterns/design-patterns/src/main/java/com/baeldung/visitor/XmlElement.java b/patterns/design-patterns/src/main/java/com/baeldung/visitor/XmlElement.java
new file mode 100644
index 0000000000..41998de428
--- /dev/null
+++ b/patterns/design-patterns/src/main/java/com/baeldung/visitor/XmlElement.java
@@ -0,0 +1,12 @@
+package com.baeldung.visitor;
+
+public class XmlElement extends Element {
+
+    public XmlElement(String uuid) {
+        super(uuid);
+    }
+
+    public void accept(Visitor v) {
+        v.visit(this);
+    }
+}
\ No newline at end of file