Questions and Answers
Objects have two properties. One is state. What is the other?
Behavior
The state of an object is stored in _____ _____
Instance variables
The behavior of an object is represented by ______ ______
Instance methods
The job of a _____ is to initialize instance variables at the time an object is created.
Signup and view all the answers
Nested inside a class declaration are three kinds of declarations. What are they?
Signup and view all the answers
The words public and private are _____ _____
Signup and view all the answers
A method is allowed to have _______, which represent data that will be supplied when the method is called.
Signup and view all the answers
Once a class has been declared, we can create objects that belong to the class. We say that these objects are ______ of the class.
Signup and view all the answers
An object variable doesn't actually store an object. Instead, it stores a ______ to an object.
Signup and view all the answers
The keyword ______ is placed before a class name in order to create an object.
Signup and view all the answers
To perform an operation on an object, we _______ one of the instance methods associated with the object.
Signup and view all the answers
How do you call an instance method?
Signup and view all the answers
Reference variables are known as _______ variables in other programming languages.
Signup and view all the answers
What value can we assign to an object variable to indicate that it doesn't currently store an object?
Signup and view all the answers
A new object that's been created by copying an existing object is said to be a _______.
Signup and view all the answers
An object that's no longer accessible through any object variable is said to be _______.
Signup and view all the answers
An instance method that returns the value of an instance variable is said to be an _______.
Signup and view all the answers
An instance method that stores its parameter into an instance variable is said to be an ________.
Signup and view all the answers
An object whose instance variables cannot be changed is said to be _______.
Signup and view all the answers
A method that returns the contents of an object as a string should be named ______.
Signup and view all the answers
The act of joining two strings together to form a single string is called _______.
Signup and view all the answers
Which method is used to remove extra space from the beginning and end of a string?
Signup and view all the answers
What is the value of 11 + 38 + 'THX'?
Signup and view all the answers
Study Notes
Key Concepts of Java: Classes and Objects
- Objects Properties: Every object has state and behavior; state refers to its condition, while behavior defines its actions.
- State Storage: The state of an object is maintained through instance variables.
- Behavior Representation: Instance methods serve to express an object's behavior.
- Constructor Role: A constructor is responsible for initializing instance variables when an object is instantiated.
- Declarations in Classes: Classes include three main types of declarations: constructor declarations, variable declarations, and method declarations.
Access Modifiers and Method Parameters
- Access Modifiers: Keywords like public and private are used to define access control for classes and class members, categorized as access modifiers.
- Method Parameters: Methods can accept parameters, which are the data inputs provided when a method is invoked.
Object Instances and References
- Object Creation: After declaring a class, objects can be created as instances of that class.
- Object Reference: An object variable does not hold the object itself but instead maintains a reference to the object.
Object Creation and Method Invocation
-
Object Instantiation: The keyword
newis used to instantiate a new object from a class. -
Calling Methods: To execute an operation on an object, invoke its instance methods using the syntax
object.methodname(arguments).
Variable Concepts and Object Lifecycle
- Reference Variables: In other programming languages, reference variables are often called pointers.
-
Indicating No Object: The value
nullcan be assigned to an object variable to signify it does not currently refer to an object. - Object Cloning: A new object created by duplicating an existing object is referred to as a clone.
- Garbage Collection: An object is considered garbage when there are no remaining references to it.
Accessor and Mutator Methods
- Accessor Methods: Methods that retrieve the value of instance variables are known as accessors or getters.
- Mutator Methods: Methods that update instance variables are classified as mutators or setters.
- Immutable Objects: An object whose instance variables cannot be altered is termed immutable.
String Handling in Java
-
toString Method: A method intended to return an object’s content as a string should be named
toString. - String Concatenation: The process of merging two strings into one is termed concatenation.
-
Trim Method: The
trimmethod is utilized to eliminate whitespace from both the beginning and the end of a string. -
Expression Evaluation: The expression
11 + 38 + "THX"evaluates to49THX, demonstrating Java's handling of string concatenation with numbers.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Description
Explore key concepts in Java related to classes and objects with these flashcards. Learn about object properties such as state and behavior, along with instance variables and methods. Perfect for students eager to master Java fundamentals!
