Add class diagram

methoden.md

@@ -45,13 +45,13 @@ Methoden werden über ihren Identifier aufgerufen. Alle deklarierten Parameter *
 
 ```java
 public void main(String[] args) {
-	int sides = 10;
-	int area = getSpuareArea(sides);
+	int radius = 10;
+	double area = getCircleArea(radius);
 	System.out.printf("The area of the square is %d", area);
 }
 
 public double getCircleArea(double radius) {
-	int result = 3.141 * radius * radius;
+	double result = 3.141 * radius * radius;
 	return result;
 }
 ```