AP Computer Science A:: Using Objects

In object-oriented programming, what is a CLASS?

- **A)** A synonym for a primitive data type
- **B)** A single specific instance of data stored in memory
- **C)** A blueprint or template that defines the properties (instance variables) and behaviors (methods) that its objects will have
- **D)** A method that returns no value

What is an OBJECT, as distinguished from a CLASS?

- **A)** A specific instance created from a class, with its own actual values stored in its instance variables
- **B)** A synonym for a class -- the two terms are always interchangeable
- **C)** The blueprint that defines what instance variables and methods will exist
- **D)** A method inside a class

Which line of code correctly declares AND instantiates a \(String\) object named \(name\) using the \(new\) keyword?

- **A)** \(String\ name = new\ String("Alex");\)
- **B)** \(new\ String\ name = "Alex";\)
- **C)** \(String\ new\ name = "Alex";\)
- **D)** \(name = String("Alex");\)

What are the THREE steps involved in creating and using an object in Java?

- **A)** Casting, printing, and looping
- **B)** Only a single step: instantiation
- **C)** DECLARATION (creating a reference variable of the class type), INSTANTIATION (using \(new\) to create the actual object in memory), and INITIALIZATION (the constructor setting up the object's initial state)
- **D)** Declaration, deletion, and re-declaration

What is a CONSTRUCTOR in a Java class?

- **A)** A method that destroys an object when it is no longer needed
- **B)** A variable that stores the class's name as a String
- **C)** A special method, with the same name as the class and no return type, that runs automatically when an object is created with \(new\), used to initialize the object's instance variables
- **D)** A method that must return an \(int\)

What is the difference between calling a VOID method and calling a method that RETURNS a value?

- **A)** Only value-returning methods can accept parameters
- **B)** A void method performs an action but gives back no value (so it cannot be used on the right side of an assignment), while a method with a return type gives back a value that can be stored in a variable or used in an expression
- **C)** Void methods and value-returning methods behave identically in every respect
- **D)** A void method always returns the value \(0\)

Given \(String\ s = "Hello";\), what does \(s.length()\) return?

- **A)** \(5\)
- **B)** \("Hello"\)
- **C)** \(6\)
- **D)** \(4\)

Given \(String\ s = "Hello";\), what does \(s.charAt(1)\) return?

- **A)** \('l'\)
- **B)** \('H'\)
- **C)** \(1\)
- **D)** \('e'\)