Class Variables, Scope, and this

Unit 3: Class Creation. Topics 3.7–3.9. This set has 56 questions. Each time the page loads you get five of them, chosen at random. Pick an answer, press Check answer, and read the explanation for every choice. Reload the page or use New questions for a fresh five.

Topics assessed

• 3.7 Class Variables and Methods
• 3.8 Scope and Access
• 3.9 this Keyword

Practice questions

Essential knowledge for this set

These are the essential knowledge (EKS) statements from the AP Computer Science A Course and Exam Description that the 56 questions in this set assess, grouped by topic and learning objective. The table under each question links here.

Topic 3.7: Class Variables and Methods

3.7.A — Develop code to define behaviors of a class through class methods.

• 3.7.A.1 Class methods cannot access or change the values of instance variables or call instance methods without being passed an instance of the class via a parameter.
• 3.7.A.2 Class methods can access or change the values of class variables and can call other class methods.

3.7.B — Develop code to declare the class variables that belong to the class.

• 3.7.B.1 Class variables belong to the class, with all objects of a class sharing a single copy of the class variable. Class variables are designated with the static keyword before the variable type.
• 3.7.B.2 Class variables that are designated public are accessed outside of the class by using the class name and the dot operator, since they are associated with a class, not objects of a class.
• 3.7.B.3 When a variable is declared final, its value cannot be modified.

Topic 3.8: Scope and Access

3.8.A — Explain where variables can be used in the code.

• 3.8.A.1 Local variables are variables declared in the headers or bodies of blocks of code. Local variables can only be accessed in the block in which they are declared. Since constructors and methods are blocks of code, parameters to constructors or methods are also considered local variables. These variables may only be used within the constructor or method and cannot be declared to be public or private.
• 3.8.A.2 When there is a local variable or parameter with the same name as an instance variable, the variable name will refer to the local variable instead of the instance variable within the body of the constructor or method.

Topic 3.9: this Keyword

3.9.A — Develop code for expressions that are self-referencing and determine the result of these expressions.

• 3.9.A.1 Within an instance method or a constructor, the keyword this acts as a special variable that holds a reference to the current object— the object whose method or constructor is being called.
• 3.9.A.2 The keyword this can be used to pass the current object as an argument in a method call.
• 3.9.A.3 Class methods do not have a this reference.