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Questions and Answers
Why are user-defined classes used?
Why are user-defined classes used?
- They enable representation of complex objects. (correct)
- They provide unlimited data representation.
- They are not used in programming.
- They only use primitive data types.
What is a class?
What is a class?
Combines data and the methods that operate on the data.
A class is a ______ (think 'cookie cutter').
A class is a ______ (think 'cookie cutter').
template
An object is an ______ of a class (think cookie).
An object is an ______ of a class (think cookie).
That said, there are _____ ______ ____ tied to the class instead of an object.
That said, there are _____ ______ ____ tied to the class instead of an object.
A _____ of a class is a program that uses that class.
A _____ of a class is a program that uses that class.
Java can have ____ constructors.
Java can have ____ constructors.
In Java, class/object variables must be ____.
In Java, class/object variables must be ____.
In Java, everything has to have a type, including the ____ ____ of methods.
In Java, everything has to have a type, including the ____ ____ of methods.
Match the following terms with their descriptions:
Match the following terms with their descriptions:
What are instance variables?
What are instance variables?
What are class variables?
What are class variables?
Both types are available to ___ the methods.
Both types are available to ___ the methods.
Each ____ in the class contains code that can manipulate one (or more) of the fields.
Each ____ in the class contains code that can manipulate one (or more) of the fields.
What are members in the context of a class?
What are members in the context of a class?
What does an access modifier do?
What does an access modifier do?
Methods of the same class and methods of other classes can be declared as _____
Methods of the same class and methods of other classes can be declared as _____
Methods of the same class only can be declared as _____
Methods of the same class only can be declared as _____
Methods of the same class, methods of subclasses, and methods of classes in the same package can be declared as _____
Methods of the same class, methods of subclasses, and methods of classes in the same package can be declared as _____
Methods in the same package only are declared with _____.
Methods in the same package only are declared with _____.
____ variables are usually declared to be private.
____ variables are usually declared to be private.
_____ that will be called by clients of the class are usually declared public.
_____ that will be called by clients of the class are usually declared public.
Methods that are _____ called by other methods of the ____ class, are declared private.
Methods that are _____ called by other methods of the ____ class, are declared private.
You may only have one class declared as public per _____, and the file name must match the class name with the extension '.java'.
You may only have one class declared as public per _____, and the file name must match the class name with the extension '.java'.
What is encapsulation?
What is encapsulation?
What is another term for information hiding?
What is another term for information hiding?
Encapsulation is the idea that clients of the class do not ____ how the class is implemented.
Encapsulation is the idea that clients of the class do not ____ how the class is implemented.
Encapsulation allows you to protect the ____ of the object's data.
Encapsulation allows you to protect the ____ of the object's data.
It allows you to change how the class is implemented without causing code that used the object to _____.
It allows you to change how the class is implemented without causing code that used the object to _____.
How do we access private instance variables?
How do we access private instance variables?
Can we add one to the current value this way? ins.setValue(getValue() + 1)
Can we add one to the current value this way? ins.setValue(getValue() + 1)
What does Validation ensure?
What does Validation ensure?
Do not give the ______ the same name as the instance variable.
Do not give the ______ the same name as the instance variable.
What are constructors?
What are constructors?
What is an example of a class in Java that has ten different constructors?
What is an example of a class in Java that has ten different constructors?
In Java, the ____ is not passed as an explicit parameter.
In Java, the ____ is not passed as an explicit parameter.
A constructor ______ (some or all) of the instance variables for the new object.
A constructor ______ (some or all) of the instance variables for the new object.
Constructors do not have a ______.
Constructors do not have a ______.
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Study Notes
User-Defined Classes Overview
- User-defined classes enhance data representation beyond primitive data types like int, long, or double, allowing for more complex object modeling.
- A class amalgamates related data and methods designed to operate on that data.
Class Concepts
- A class acts as a template, akin to a cookie cutter, guiding the creation of objects.
- An instance is a specific object created from a class, comparable to a cookie made from the cookie cutter.
Class Composition
- Classes can include fields and methods, with fields storing data and methods performing actions on that data.
- Class members encompass both fields (data variables) and methods (functions associated with the class).
Java Class Features
- Java allows multiple constructors, providing variations in object instantiation.
- Variables in Java must be explicitly declared, ensuring clear data structures.
Method and Return Value
- Every method in Java should have an associated type, including the return value.
- Constructor methods are special, serving to initialize fields when an object is created.
Access Modifiers
- Access modifiers control visibility and accessibility of class components:
- public: accessible from outside the class.
- private: only accessible within the same class.
- protected: accessible within the same class, subclasses, and same package.
- No modifier: accessible within the same package.
Encapsulation and Data Integrity
- Encapsulation promotes information hiding, ensuring class implementation details are not exposed to clients.
- This protects data integrity and allows for internal changes without affecting external code relying on the object.
Accessing Private Variables
- Private instance variables can be accessed through accessor (getter) and mutator (setter) methods, facilitating controlled data manipulation.
Constructors Role and Functionality
- Constructors have no return type and are invoked when a new object is created, initializing instance variables.
- Ensuring constructors do not use the same names as instance variables is critical for clarity.
Class Examples
- The Scanner class in Java is an example featuring multiple constructors, illustrating flexibility in object creation.
Summary
- Understanding user-defined classes, syntax, access control, and encapsulation is crucial for effective object-oriented programming in Java.
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