added memento sample

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);
+	}
+}