added memento sample

memento/src/main/java/com/iluwatar/App.java

@@ -0,0 +1,30 @@
+package com.iluwatar;
+
+import java.util.Stack;
+
+public class App 
+{
+    public static void main( String[] args )
+    {
+    	Stack<StarMemento> states = new Stack<>();
+    	
+    	Star star = new Star(StarType.SUN, 10000000, 500000);
+    	System.out.println(star);
+    	states.add(star.getMemento());
+    	star.timePasses();
+    	System.out.println(star);
+    	states.add(star.getMemento());
+    	star.timePasses();
+    	System.out.println(star);
+    	states.add(star.getMemento());
+    	star.timePasses();
+    	System.out.println(star);
+    	states.add(star.getMemento());
+    	star.timePasses();
+    	System.out.println(star);
+    	while (states.size() > 0) {
+    		star.setMemento(states.pop());
+        	System.out.println(star);
+    	}
+    }
+}

memento/src/main/java/com/iluwatar/Star.java

@@ -0,0 +1,63 @@
+package com.iluwatar;
+
+public class Star {
+	
+	private StarType type;
+	private int ageYears;
+	private int massTons;
+	
+	public Star(StarType startType, int startAge, int startMass) {
+		this.type = startType;
+		this.ageYears = startAge;
+		this.massTons = startMass;
+	}
+	
+	public void timePasses() {
+		ageYears *= 2;
+		massTons *= 8;
+		switch (type) {
+		case RED_GIANT:
+			type = StarType.WHITE_DWARF;
+			break;
+		case SUN:
+			type = StarType.RED_GIANT;
+			break;
+		case SUPERNOVA:
+			type = StarType.DEAD;
+			break;
+		case WHITE_DWARF:
+			type = StarType.SUPERNOVA;
+			break;
+		case DEAD:
+			ageYears *= 2;
+			massTons = 0;
+			break;
+		default:
+			break;
+		}
+	}
+	
+	StarMemento getMemento() {
+
+		StarMementoInternal state = new StarMementoInternal();
+		state.setAgeYears(ageYears);
+		state.setMassTons(massTons);
+		state.setType(type);
+		return state;
+		
+	}
+	
+	void setMemento(StarMemento memento) {
+		
+		StarMementoInternal state = (StarMementoInternal) memento;
+		this.type = state.getType();
+		this.ageYears = state.getAgeYears();
+		this.massTons = state.getMassTons();
+		
+	}
+	
+	@Override
+	public String toString() {
+		return String.format("%s age: %d years mass: %d tons", type.toString(), ageYears, massTons);
+	}
+}

memento/src/main/java/com/iluwatar/StarMemento.java

@@ -0,0 +1,5 @@
+package com.iluwatar;
+
+public interface StarMemento {
+
+}

memento/src/main/java/com/iluwatar/StarMementoInternal.java

@@ -0,0 +1,27 @@
+package com.iluwatar;
+
+public class StarMementoInternal implements StarMemento {
+
+	private StarType type;
+	private int ageYears;
+	private int massTons;
+	
+	public StarType getType() {
+		return type;
+	}
+	public void setType(StarType type) {
+		this.type = type;
+	}
+	public int getAgeYears() {
+		return ageYears;
+	}
+	public void setAgeYears(int ageYears) {
+		this.ageYears = ageYears;
+	}
+	public int getMassTons() {
+		return massTons;
+	}
+	public void setMassTons(int massTons) {
+		this.massTons = massTons;
+	}
+}

memento/src/main/java/com/iluwatar/StarType.java

@@ -0,0 +1,36 @@
+package com.iluwatar;
+
+public enum StarType {
+
+	SUN,
+	RED_GIANT,
+	WHITE_DWARF,
+	SUPERNOVA,
+	DEAD;
+
+	@Override
+	public String toString() {
+		String s = "";
+		switch (this) {
+		case RED_GIANT:
+			s = "red giant";
+			break;
+		case SUN:
+			s = "sun";
+			break;
+		case SUPERNOVA:
+			s = "supernova";
+			break;
+		case WHITE_DWARF:
+			s = "white dwarf";
+			break;
+		case DEAD:
+			s = "dead star";
+			break;
+		default:
+			break;
+		}
+		return s;
+	}
+	
+}