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Unit 2: Using Objects

9 dot points across 9 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How does a non-void method return a value, and how do you use that returned value?

Topic 2.5 Calling a Non-void Method: call a method that returns a value, and use the returned value by storing it, printing it, or including it in an expression.
A focused answer to AP CSA Topic 2.5, covering methods that return a value, the return type, using a returned value in an assignment, expression or print, the difference from a void method, and chaining method calls, with a worked trace.
9 min answer →

How do you pass arguments to a void method, and how do parameters and arguments correspond?

Topic 2.4 Calling a Void Method with Parameters: call a void method that takes parameters, passing arguments that match the parameter list in number, order and type, and explain how arguments are copied to parameters.
A focused answer to AP CSA Topic 2.4, covering parameters versus arguments, matching the argument list in number, order and type, pass-by-value for primitives, overloaded methods, and how the call supplies data to the method, with a worked trace.
9 min answer →

How do you call a void method on an object using dot notation, and what does void mean?

Topic 2.3 Calling a Void Method: call a non-static void method on an object using dot notation, and explain that a void method performs an action but returns no value.
A focused answer to AP CSA Topic 2.3, covering dot notation for calling methods on objects, what void means, why a void call cannot be used in an expression, the difference between a method signature and a call, and method side effects, with a worked example.
8 min answer →

How do you create an object with the new keyword and a constructor, and store it in a reference variable?

Topic 2.2 Creating and Storing Objects (Instantiation): use the new keyword to call a constructor and instantiate an object, choosing the correct constructor by its parameters, and store the result in a reference variable.
A focused answer to AP CSA Topic 2.2, covering the new keyword, constructors and how they initialise an object, choosing a constructor by its parameter list, matching argument types, storing the reference, and the meaning of null, with a worked example.
9 min answer →

What is the relationship between a class and an object, and what does it mean to say an object is an instance of a class?

Topic 2.1 Objects: Instances of Classes: explain the relationship between a class and its objects, and describe an object as an instance of a class with state and behavior.
A focused answer to AP CSA Topic 2.1, covering the class-object relationship, what it means for an object to be an instance, the difference between attributes (state) and methods (behavior), and reference versus primitive variables, with a worked example.
8 min answer →

How are String objects created and joined, and what does string concatenation do with different operand types?

Topic 2.6 String Objects: Concatenation, Literals, and More: create String objects from literals or a constructor, concatenate strings with the + operator, and predict the result of mixing strings with numbers and escape sequences.
A focused answer to AP CSA Topic 2.6, covering String literals and the String constructor, concatenation with the plus operator, the rule that any value concatenated with a String becomes a String, left-to-right evaluation traps, and escape sequences, with a worked trace.
9 min answer →

Which String methods does AP CSA require, and how do length, substring, indexOf, equals and compareTo behave?

Topic 2.7 String Methods: call the String methods in the AP Java subset (length, substring, indexOf, equals, compareTo), respecting zero-based indexing and the immutability of String objects.
A focused answer to AP CSA Topic 2.7, covering the required String methods length, substring (both forms), indexOf, equals and compareTo, zero-based indexing, the half-open range of substring, why == differs from equals, and String immutability, with a worked trace.
11 min answer →

Which Math class methods does AP CSA require, and how do you generate a random number in a chosen range?

Topic 2.9 Using the Math Class: call the static Math methods in the AP Java subset (abs, pow, sqrt, random) and generate a random integer or double in a specified range.
A focused answer to AP CSA Topic 2.9, covering the required static Math methods abs, pow, sqrt and random, why Math methods are called on the class, the return types, and the standard formula for generating a random int in a range, with a worked trace.
10 min answer →

What are the Integer and Double wrapper classes, and how do autoboxing, unboxing and their useful constants and methods work?

Topic 2.8 Wrapper Classes: Integer and Double: use the Integer and Double wrapper classes, including autoboxing and unboxing, the MIN_VALUE and MAX_VALUE constants, and parsing methods.
A focused answer to AP CSA Topic 2.8, covering why wrapper classes exist, creating Integer and Double objects, autoboxing and unboxing, Integer.MIN_VALUE and MAX_VALUE, parseInt and parseDouble, and the == versus equals trap for wrappers, with a worked trace.
10 min answer →