2段階目（抽象クラスとインターフェースを使ってみよう）

em-oop/src/Day3Check2.java

@@ -0,0 +1,14 @@
+
+public class Day3Check2 {
+
+	public static void main(String[] args) {
+		Rectangle rectangle = new Rectangle(3, 4);
+		rectangle.showInfo();
+		Greeting jpGreeting = new JapaneseGreeting();
+		System.out.println(jpGreeting.hello());
+		LoudGreeting jpShout = new JapaneseGreeting();
+		System.out.println(jpShout.shout());
+
+	}
+
+}

em-oop/src/Greeting.java

@@ -0,0 +1,4 @@
+
+public interface Greeting {
+	String hello();
+}

em-oop/src/JapaneseGreeting.java

@@ -0,0 +1,14 @@
+
+public class JapaneseGreeting implements Greeting, LoudGreeting {
+
+	@Override
+	public String hello() {
+		return "こんにちは";
+	}
+
+	@Override
+	public String shout() {
+		return "やっほー！";
+	}
+
+}

em-oop/src/LoudGreeting.java

@@ -0,0 +1,4 @@
+
+public interface LoudGreeting {
+	String shout();
+}

em-oop/src/Rectangle.java

@@ -0,0 +1,18 @@
+
+public class Rectangle extends Shape {
+
+	private double width;
+	private double height;
+
+	public Rectangle(double width, double height) {
+		super("四角形");
+		this.width = width;
+		this.height = height;
+	}
+
+	@Override
+	public double area() {
+		return width * height;
+	}
+
+}

em-oop/src/Shape.java

@@ -1,14 +1,12 @@
 
-public class Shape {
+public abstract class Shape {
 	private String name;
 
 	public Shape(String name) {
 		this.name = name;
 	}
 
-	public double area() {
-		return 0.0;
-	}
+	public abstract double area();
 
 	public void showInfo() {
 		System.out.println(this.name + "の面積は" + this.area() + "です");