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Questions and Answers
What is the total weekly salary for an individual earning R250 per hour who works 8 hours a day for 5 days?
How must the method name in Java be structured?
What does a return statement do in a Java method?
What is a characteristic of a constructor in Java?
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Which of the following best describes data hiding in object-oriented programming?
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What is a method in programming?
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Which of the following components is NOT included in the method header?
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In which part must a method be placed?
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What is the purpose of access specifiers in methods?
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Which method executes automatically when a Java application starts?
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Study Notes
Understanding Method Calls and Placement
- A method is a program module that contains a series of statements and performs a specific task.
- To execute a method, it must be invoked or called from another method.
- The calling method is also known as the client method.
- The called method is the method that is invoked by the calling method.
- The main() method executes automatically, while other methods are called as needed.
Understanding Method Construction
- Every method has a method header and a method body.
- The method header includes optional access specifiers, a return type, an identifier, and parentheses.
- The method body is enclosed in curly braces and contains the statements that perform the work.
Access Specifiers
- Methods can have different access specifiers: public, private, protected, or package.
- Public access allows any other class to use the method.
- Access specifiers are also called access modifiers.
- Public access is the most common for methods.
Return Type
- The return type specifies the type of data the method sends back to the calling method.
- If the method does not return any data, the return type is void.
Method Name
- Method names must be legal identifiers.
- They must be one word with no embedded spaces and cannot be Java keywords.
Parentheses
- Each method header has a set of parentheses following the identifier.
- The parentheses may contain data to be sent to the method.
- A fully qualified identifier includes the class name and the method name.
Adding Parameters to Methods
- Arguments provide data items in a method call.
- Parameters receive the data items from the method call.
- Implementation hiding encapsulates method details within a class.
- The calling method only needs to understand the interface of the called method.
- The interface is the only part of the method that the client interacts with.
Creating a Method that Receives a Single Parameter
The method declaration needs to specify:
- Optional access specifiers
- Return type for the method
- Method name
- Parameter type
- Local name for the parameter
- Local variables are only known within the method's boundaries.
Creating a Method That Requires Multiple Parameters
- A method can take multiple parameters.
- Arguments in the method call are separated by commas.
- The number and type of arguments must match the parameters in the method declaration.
Creating Methods That Return Values
- The return statement sends a value back to the calling method.
- The return type can be any type used in Java.
- Unreachable statements, or dead code, cannot be executed due to a return statement.
Chaining Method Calls
- Methods can call other methods, forming a chain of calls.
- The calling method does not need to know how the called method works.
Learning About Classes and Objects
- Objects are members of a class.
- Is-a relationships are when an object is a concrete example of a class.
- Instantiation is the creation of an object from a class.
- Reusability refers to the ability to use the same class to create multiple objects.
Creating a Class
- Class headers have three parts: access modifier, the keyword class, and the class name.
- Public classes are accessible by all objects.
- Data fields are variables declared within a class but outside of any method.
- Instance variables are nonstatic fields specific to each object.
- Private fields are only accessible within the same class.
- Most class methods are public.
Creating Instance Methods in a Class
- Classes contain mutator methods (change field values) and accessor methods (retrieve values).
- Nonstatic methods are instance methods that belong to individual objects.
- Data fields are typically nonstatic.
- Static class variables are not instance variables.
Organizing Classes
- Data fields are typically placed at the beginning of the class.
- The order of methods within a class is flexible, but they are often placed after data fields for clarity.
Declaring Objects and Using Their Methods
- Declaring a class does not create any objects.
- To create an object, use the new operator with the class type and identifier.
- The object's name refers to the memory address where the object is stored.
- Constructor methods create and initialize objects.
- Every class has a default constructor if one is not explicitly defined.
- The constructor name matches the class name.
- The constructor has no return type and has public access.
Understanding Data Hiding
- Encapsulation uses private data fields and public access methods to hide data implementation details.
- Set methods set or change the values of variables.
- Get methods retrieve variable values.
An Introduction to Using Constructors
- The
newoperator implicitly calls the constructor method. - Default constructors are automatically provided by the Java compiler.
- The default constructor initializes numeric fields to 0, character fields to Unicode ‘\u0000’, boolean fields to false, and nonprimitive object fields to null.
Understanding that Classes Are Data Types
- Classes create new data types, often referred to as abstract data types (ADTs), which are hidden from the user and accessed through public methods.
- Classes offer programmer-defined data types, not built into the language.
- Objects of a class can be declared using the class name as the type and identifier.
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Description
This quiz tests your knowledge of method calls and construction in programming languages. You'll learn about the roles of calling and called methods, method headers, and access specifiers. Perfect for students studying programming fundamentals.
