Peer Instruction: Unit 2 Turtle Multiple Choice Questions

2-14-1: 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.

2-14-2: 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.

2-14-3: 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.

2-14-4: 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.

You have attempted of activities on this page