Questions and Answers
What is an object in Java?
An object is something that contains both state and behavior.
What is the difference between a class and an object?
Objects are instances of classes. The class is the general template, and the object is the specific version.
What does it mean to be a client of a class?
Being a client of a class means that we can use its methods and functionality without necessarily understanding how it works.
What is a constructor in Java?
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Which of the following is the correct code for the constructor in the Card class?
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What is an instance method?
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Which of the following is correct code? I.
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What is the difference between a getter method and an accessor method?
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Which of these is an example of calling a static method?
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Double sum(int one, double two)
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Which variables are in scope at the point labeled // POINT A?
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What is printed by the following program?
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What is the this keyword?
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What is the output of the following code snippet?
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What is the output of the following code snippet?
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How do you call the superconstructor from a subclass?
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Which of the following is a false statement about the classes?
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Say you are trying to create a set of classes that represent tools. Which is the proper first line of each class?
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What is the definition of polymorphism?
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What method must a class contain to implement the Comparable interface?
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Study Notes
Objects and Classes
- An object in Java is a combination of state (data) and behavior (methods).
- Classes serve as templates or blueprints for creating objects, while objects represent specific instances of those classes.
Class Clients and Constructors
- A class client utilizes the class's methods without needing to know the internal workings.
- Constructors are special methods used to instantiate a class and initialize its properties when creating an object.
Instance Methods and Accessors
- Instance methods operate on a specific instance of a class and are invoked on a particular object.
- Getter methods and accessor methods are interchangeable terms, both referring to methods that retrieve values of object properties.
Static Methods and Calling Conventions
- Example of a static method call:
Math.abs(x)
, which computes the absolute value ofx
. - Method signatures may vary, as illustrated in function definitions like
double sum(int one, double two)
.
Scope and the 'this' Keyword
- At a specific code point labeled "// POINT A," only variables named
sum
andcount
exist in the current scope. - The
this
keyword refers to the current object instance, emphasizing the context of which object's methods or properties are being accessed.
Inheritance and Superconstructor
- To invoke a constructor from a parent class within a subclass, use the
super
keyword in the subclass's constructor. - Inheritance implies that subclasses like SciFi and Fantasy do not inherit constructors directly from their parent class Movie.
Class Declaration and Polymorphism
- Subclass examples include
public class Hammer extends Tool
andpublic class Screwdriver extends Tool
, indicating the relationship with the parent Tool class. - Polymorphism enables methods to operate differently based on the object type they are applied to, allowing for dynamic behavior in programming.
Comparable Interface
- To implement the Comparable interface, a class must define the method
public int compareTo(T other)
, which facilitates object comparison.
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Description
Test your knowledge of Java's object-oriented principles with this quiz. Explore key concepts such as objects, classes, and client relationships within Java programming. Perfect for beginners to deepen their understanding of OOP.