Peer Instruction: Unit 2 Turtle Multiple Choice Questions

16-6-1: What are the components of the second line of code?

Turtle turtle1 = new Turtle();
turtle1.turn(-45);

• Type, method/message name, parameter list
• Incorrect! Turtle is a "type" (similar to int or double types) but turtle1 is an object. An object is an instance of a class. In this case, turtle1 is an instance of the Turtle class.
• Class, method/message name, parameter list
• Incorrect! Turtle is the specific class "type" that turtle1 is. turtle1 itself is an object. An object is an instance of a class. In this case, turtle1 is an instance of the Turtle class.
• Object, method/message name, parameter list
• Correct! turtle1 is a Turtle object. An object is an instance of a class. In this case, turtle1 is an instance of the Turtle class.

16-6-2: Why is this code incorrect? Assume this method is a method of the Turtle class (There are multiple correct answers)

public bethsSquare(int size) {
    turtle1.turnLeft();
    turtle1.forward(100);
    turtle1.turnLeft();
    turtle1.forward(100);
    turtle1.turnLeft();
    turtle1.forward(100);
    turtle1.turnLeft();
    turtle1.forward(100);
}

• Nothing is incorrect
• Incorrect! There are multiple places where the code is incorrect.
• Return type is wrong
• Correct! This is a method of the Turtle class. It should have a return type of void. It doesn’t produce a number – it causes an action to happen.
• Parameter is used incorrectly
• Correct! The bethsSquare parameter "size" is not used in the method. Perhaps it could replace the "100" in the method calls (ex. turtle1.forward(size)).
• turnLeft should be turnRight
• Incorrect! Although it is true that you could use turnRight instead of turnLeft, this is not necessarily an incorrect aspect of the code because turnLeft still produces the expected response.
• Use of turtle1 is incorrect
• Correct! Because this is a method of the turtle class, it is callable by any turtle object. Whichever turtle calls it is the turtle that should be controlled (turned, moved forward). The object ``this`` can be used instead of ``turtle1`` to refer to the object performing the method.

16-6-3: What’s the right way to call the bethsSquare method to draw a square (void method that takes one parameter)?

• World w = new World();
  Turtle t = new Turtle(10,10, w);
  t = bethsSquare(50);
  

• Incorrect! bethsSquare is a void method, and it doesn’t return anything, so t should not equal bethsSquare(50).

• World w = new World();
  Turtle t = new Turtle(10,10, w);
  t.bethsSquare();
  

• Incorrect! bethsSquare has a parameter which is not accounted for.

• World w = new World();
  Turtle t = new Turtle(10,10, w);
  t.bethssquare();
  

• Incorrect! bethsSquare has a parameter which is not accounted for, and the method call is spelled with a lowercase ‘s’ instead of an uppercase ‘s.’

• World w = new World();
  Turtle t = new Turtle(10,10, w);
  t = bethssquare(50);
  

• Incorrect! bethsSquare is a void method, and it doesn’t return anything, so t should not equal bethsSquare(50). Additionally, the method call is spelled with a lowercase ‘s’ instead of an uppercase ‘s.’

• None of the above

• Correct! The correct “call” to the method to draw a square would be t.bethSquare(50), accounting for the fact that that the method is void, the correct spelling of the method, and the parameter.

16-6-4: What types are returned by these method calls?

// 1)
turtle1.turnLeft();
// 2)
turtle1.getName();
// 3)
FileChooser.pickAFile();
// 4)
new Picture();

• main, main, Picture, String
• Incorrect! In the Turtle class, turnLeft returns void. getName returns a String. The pickAFile method returns the name of the file, a String. new Picture() calls the constructor to make a new Picture object, so it returns an object of type Picture.
• void, void, Picture, String
• Inorrect! In the Turtle class, getName returns a String. The pickAFile method returns the name of the file, a String. new Picture() calls the constructor to make a new Picture object, so it returns an object of type Picture.
• Turtle, Turtle, Picture, String
• Incorrect! In the Turtle class, turnLeft returns void. getName returns a String. The pickAFile method returns the name of the file, a String. new Picture() calls the constructor to make a new Picture object, so it returns an object of type Picture.
• void, void, String, Picture
• getName returns a String rather than void.
• None of the above
• Correct! In the Turtle class, turnLeft returns void. getName returns a String. The pickAFile method returns the name of the file, a String. new Picture() calls the constructor to make a new Picture object, so it returns an object of type Picture.

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