memento added

Author: maciej-nowak

memento/README.md

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+# memento
+
+This is repository of http://androidcode.pl blog. It shows uses of Memento in Android. It is a part of Design Patterns - Memento post in the blog.

memento/example/Document.java

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+public class Document {
+
+    private String text;
+    private String name;
+    private long timestamp;
+
+    public Answer(String name) {
+        this.name = name;
+        this.text = "";
+        this.timestamp = System.currentTimeMillis();
+    }
+
+    public void setText(String text) {
+        this.text = text;
+        this.timestamp = System.currentTimeMillis();
+    }
+
+    public void setName(String name) {
+        this.name = name;
+        this.timestamp = System.currentTimeMillis();
+    }
+
+    public Memento save() {
+        return new Memento(name, text, timestamp);
+    }
+
+    public void restore(Memento memento) {
+        this.name = memento.name;
+        this.text = memento.text;
+        this.timestamp = memento.timestamp;
+    }
+
+    class Memento {
+
+        private String name;
+        private String text;
+        private long timestamp;
+
+        public Memento(String name, String text, long timestamp) {
+            this.name = name;
+            this.text = text;
+            this.timestamp = timestamp;
+        }
+
+        public String getText() {
+            return text;
+        }
+
+        public int getOption() {
+            return option;
+        }
+    }
+}

memento/example/DocumentManager.java

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+public class DocumentManager {
+
+    private List<Memento> mementos = new ArrayList<>();
+    private int current = 0;
+
+    public void add(Memento memento) {
+        mementos.add(memento);
+        current++;
+    }
+
+    public Memento redo() {
+        if(current < mementos.size() - 1)
+            current += 1;
+        return mementos.get(current);
+    }
+
+    public Memento undo() {
+        if(current > 0)
+            current -= 1;
+        return mementos.get(current);
+    }
+
+    public Memento get(int number) {
+        if(number >= 0 && number < mementos.size())
+          return mementos.get(number);
+        else
+          return mementos.get(current);
+    }
+
+    public int historySize() {
+        return mementos.size();
+    }
+}

memento/example/Main.java

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+public class Main {
+
+	public static void main() {
+		//user open writer editor and create new empty file
+		DocumentManager manager = new DocumentManager();
+		Document document = new Document("CV.doc");
+
+		//user wrote some text into document
+		decument.setText("Begin of the text document.");
+
+		//user wrote more text
+		document.setText("Begin of the text document. More text wrote here.");
+		//autosave executed
+		manager.add(document.save()); //first document snapshot
+
+		//user change document name and wrote more text
+		document.setName("CV_ENG.doc");
+		document.setText("Begin of the text document. More text wrote here. And more text again.")
+		//autosave executed
+		manager.add(document.save()); //second document snapshot
+
+		//user removed whole text and typed new one
+		document.setText("Text wrote again.");
+		//manual save executed
+		manager.add(document.save()); //third document snapshot
+
+		//after some while user decide to restore previous document snapshot
+		document.restore(manager.undo());
+
+		//user can write text and undo, redo or choose concrete document snapshot to revert state
+	}
+}

memento/pattern/Caretraker.java

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+public class Caretaker {
+
+    private List<Memento> mementos = new ArrayList<>();
+
+    public void add(Memento memento) {
+        mementos.add(memento);
+    }
+
+    public Memento get(int index) {
+        return mementos.get(index)
+    }
+
+    public int getSize() {
+        return mementos.size();
+    }
+}

memento/pattern/Main.java

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+public class Main {
+
+	public static void main() {
+		Originator originator = new Originator();
+		Caretaker caretaker = new Caretaker();
+
+		//first step, no need to add to the history
+		originator.setState("State1");
+
+		//next step, need to add to the history
+		originator.setState("State2");
+		caretaker.add(originator.save()); //State2 has been saved
+
+		//next step, also need to save
+		originator.setState("State3");
+		caretaker.add(originator.save()); //State3 has been saved
+
+		//next step, no need to save
+		originator.setState("State4");
+
+		//user decide to back step so previous state restore
+		originator.restore(caretaker.get(caretaker.getSize() - 1));
+	}
+}

memento/pattern/Originator.java

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+public class Originator {
+
+    private String state;
+
+    public void setState(String state) {
+        this.state = state;
+    }
+
+    public Memento save() {
+        return new Memento(state);
+    }
+
+    public void restore(Memento memento) {
+        state = memento.getState();
+    }
+
+    class Memento {
+
+        private String state;
+
+        public Memento(String state) {
+            this.state = state;
+        }
+
+        public String getState() {
+            return state;
+        }
+    }
+}