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Questions and Answers
What does the + sign indicate in the context of the TV class?
What does the + sign indicate in the context of the TV class?
What is the maximum channel number that can be set for the TV object?
What is the maximum channel number that can be set for the TV object?
Which method would you call to increase the current volume level of a TV object by one?
Which method would you call to increase the current volume level of a TV object by one?
If you wanted to turn off a TV object, which method would you use?
If you wanted to turn off a TV object, which method would you use?
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In the context of the TV class, how would you denote the current state of the TV being on?
In the context of the TV class, how would you denote the current state of the TV being on?
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What does the notation 'radius: double' represent in a UML class diagram?
What does the notation 'radius: double' represent in a UML class diagram?
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Which method in the Circle class is responsible for calculating the area?
Which method in the Circle class is responsible for calculating the area?
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How are circle objects represented in the UML notation?
How are circle objects represented in the UML notation?
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What is demonstrated by the constructor 'Circle(newRadius: double)' in the Circle class?
What is demonstrated by the constructor 'Circle(newRadius: double)' in the Circle class?
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What is the purpose of the 'setRadius(newRadius: double): void' method in the Circle class?
What is the purpose of the 'setRadius(newRadius: double): void' method in the Circle class?
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How many Circle objects were created in the example above?
How many Circle objects were created in the example above?
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Which notation indicates that a method has a return type in the UML class diagram?
Which notation indicates that a method has a return type in the UML class diagram?
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What happens when the radius of circle2 is set to 100?
What happens when the radius of circle2 is set to 100?
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Which method should be defined as static according to the design guide?
Which method should be defined as static according to the design guide?
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What does the method m2(int i, int j) return?
What does the method m2(int i, int j) return?
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Why is the radius variable in the Circle class an instance variable?
Why is the radius variable in the Circle class an instance variable?
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Which statement is true regarding instance methods?
Which statement is true regarding instance methods?
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What is the result of invoking m1() given appropriate values for i and k?
What is the result of invoking m1() given appropriate values for i and k?
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What is the main reason line 6 in the first code example is incorrect?
What is the main reason line 6 in the first code example is incorrect?
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Which statement describes a valid way to access instance fields in a static context?
Which statement describes a valid way to access instance fields in a static context?
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What can be inferred about instance methods when called from a static method?
What can be inferred about instance methods when called from a static method?
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What would happen if line 7 in the first example was modified to 'A.m1();'?
What would happen if line 7 in the first example was modified to 'A.m1();'?
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In the corrected version of the code, what is the role of the line 'A a = new A();'?
In the corrected version of the code, what is the role of the line 'A a = new A();'?
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How does the line 'int j = a.i;' access the instance variable 'i' correctly?
How does the line 'int j = a.i;' access the instance variable 'i' correctly?
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What is the significance of the method 'm2' in the class A?
What is the significance of the method 'm2' in the class A?
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Which statement about static fields in the provided code is true?
Which statement about static fields in the provided code is true?
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What will the JVM do if an object is no longer referenced by any reference variable?
What will the JVM do if an object is no longer referenced by any reference variable?
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What is the purpose of assigning null to a reference variable?
What is the purpose of assigning null to a reference variable?
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Which of the following statements about arrays is accurate?
Which of the following statements about arrays is accurate?
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What type of exception is a NullPointerException?
What type of exception is a NullPointerException?
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What is an anonymous object?
What is an anonymous object?
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What can be inferred from the line 'ShowErrors t = new ShowErrors(5);' in program (a)?
What can be inferred from the line 'ShowErrors t = new ShowErrors(5);' in program (a)?
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What is the likely issue in the line 'System.out.println(c.value);' from program (d)?
What is the likely issue in the line 'System.out.println(c.value);' from program (d)?
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In program (b), which statement has an error?
In program (b), which statement has an error?
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What does the method distance(x: double, y: double) return?
What does the method distance(x: double, y: double) return?
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Which method would you invoke to get the y-coordinate of a Point2D object?
Which method would you invoke to get the y-coordinate of a Point2D object?
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In the provided program, what is printed when invoking toString() on the Point2D object p1 with coordinates (1.5, 5.5)?
In the provided program, what is printed when invoking toString() on the Point2D object p1 with coordinates (1.5, 5.5)?
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How many Point2D objects are created in the program TestPoint2D?
How many Point2D objects are created in the program TestPoint2D?
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Which line of code correctly initializes a Point2D object?
Which line of code correctly initializes a Point2D object?
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What is the output of the program if the user inputs point1 coordinates as 1.5 and 5.5 and point2 coordinates as -5.3 and -4.4?
What is the output of the program if the user inputs point1 coordinates as 1.5 and 5.5 and point2 coordinates as -5.3 and -4.4?
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What is the purpose of the main method in the program TestPoint2D?
What is the purpose of the main method in the program TestPoint2D?
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Which one of the following methods is NOT a part of the Point2D class?
Which one of the following methods is NOT a part of the Point2D class?
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Study Notes
Introduction
- Object-oriented programming (OOP) allows you to develop large-scale software and GUIs effectively.
- Java features like selections, loops, methods, and arrays are insufficient for GUI and large-scale software.
Defining Classes for Objects
- A class defines the properties (attributes) and behaviors (actions) for objects.
- Objects represent real-world entities (student, desk, circle, button, loan).
- Object state is represented by data fields (variables) with current values (e.g., a circle's radius, a rectangle's width and height).
- Object behavior is defined by methods (actions). Methods can be used to get information from an object, change its data fields, or perform another action.
Example: Circle Class
- A class template defines an object's data fields and methods.
- A class is a blueprint or contract. An object is an instance of a class.
- Data fields define the characteristics of an object (eg a circle’s radius),
- Methods define the actions an object can perform.
Defining Classes and Creating Objects
- Classes define objects.
- Objects are created from classes.
- Example code creates three circles with different radii and shows their area and perimeter.
- The code changes the radius of one circle and shows the new area and perimeter.
Constructing Objects Using Constructors
- A constructor is a special kind of method used to create objects.
- It has the same name as the class.
- It does not have a return type.
- It is invoked using the new operator.
Accessing Objects via Reference Variables
- Objects are accessed via reference variables.
- Reference variables hold references to objects.
- To access object data and methods use the dot operator with the reference variable (e.g.
objectRefVar.dataField
). - Reference variables that appear to hold objects actually hold references to them.
Reference Data Fields and the null Value
- Data fields can use reference types (e.g.
String
). - The
null
value represents the absence of reference to an object of a reference type. - Data fields have default values (
null
for reference types, 0 for numeric types, false for booleans).
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question in between every topic in the given pdf book including chapter 9,10,11,12 and13