All Flashcards
What is the main purpose of a class in Java?
To define the structure and behavior of objects.
Why are instance variables often declared as private?
To enforce encapsulation and protect data integrity.
What is the role of a constructor in object creation?
To initialize the object's state by assigning initial values to its instance variables.
How does encapsulation contribute to code maintainability?
By hiding internal implementation details and preventing unintended modifications from outside the class.
What is the significance of the 'new' keyword in Java?
It is used to create a new instance (object) of a class.
Explain the concept of information hiding.
Restricting access to certain components of a class to prevent improper access or modification.
What is the purpose of a getter method?
A method used to access the value of a private instance variable.
What is the purpose of a setter method?
A method used to modify the value of a private instance variable.
What is the role of the main method?
It is the entry point for the program.
What are the three main parts of a class?
Variable declarations, constructors, and methods.
Identify the error in the following code:
java
public class Square {
private int side;
public Square(int s) {
side = s
}
}
Missing semicolon after side = s.
What does the following code output?
java
public class Example {
public static void main(String[] args) {
Square mySquare = new Square(5);
System.out.println(mySquare.getArea());
}
}
class Square {
private int side;
public Square(int side) {
this.side = side;
}
public int getArea() {
return side * side;
}
}
25
Complete the following code snippet to create a default constructor for the Rectangle class:
java
public class Rectangle {
private int width;
private int height;
// Complete the code here
}
java
public Rectangle() {
width = 0;
height = 0;
}
Identify the error in the following code:
java
public class Circle {
private double radius;
public void Circle(double r) {
radius = r;
}
}
The constructor Circle should not have a void return type.
What does the following code output?
java
public class Test {
public static void main(String[] args) {
House myHouse = new House("123 Main St", 3);
System.out.println(myHouse.getAddress());
}
}
class House {
private String address;
private int rooms;
public House(String address, int rooms) {
this.address = address;
this.rooms = rooms;
}
public String getAddress() {
return address;
}
}
123 Main St
Complete the following code snippet to create a getter method for the make attribute of the Car class:
java
public class Car {
private String make;
// Complete the code here
}
java
public String getMake() {
return make;
}
What does the following code output?
java
public class Example {
public static void main(String[] args) {
Plant myPlant = new Plant("Rose", 1.5);
System.out.println(myPlant.getHeight());
}
}
class Plant {
private String species;
private double height;
public Plant(String species, double height) {
this.species = species;
this.height = height;
}
public double getHeight() {
return height;
}
}
1.5
Identify the error in the following code:
java
public class Student {
private String name;
public Student(name) {
this.name = name;
}
}
Missing data type in the constructor parameter declaration. Should be public Student(String name).
What does the following code output?
java
public class Example {
public static void main(String[] args) {
Phone myPhone = new Phone("Apple", "iPhone 13", "Blue");
myPhone.makeCall();
}
}
class Phone {
private String brand;
private String model;
private String color;
public Phone(String brand, String model, String color) {
this.brand = brand;
this.model = model;
this.color = color;
}
public void makeCall() {
System.out.println("Calling...");
}
}
Calling...
Complete the following code snippet to create a setter method for the rooms attribute of the House class:
java
public class House {
private int rooms;
// Complete the code here
}
java
public void setRooms(int rooms) {
this.rooms = rooms;
}
What are the general steps to writing a class in Java?
- Define the class header. 2. Declare instance variables. 3. Define constructors. 4. Define methods.
What are the steps to create a new object from a class?
- Declare a variable of the class type. 2. Use the
newkeyword followed by the class constructor to create the object. 3. Assign the newly created object to the variable.
What are the steps to access an instance variable of an object?
- Ensure the instance variable has appropriate access (e.g., public or via getter method). 2. Use the dot operator (
.) to access the variable (e.g.,objectName.variableNameorobjectName.getVariableName()).
What are the steps to call a method on an object?
- Use the dot operator (
.) followed by the method name and parentheses (e.g.,objectName.methodName()). 2. Pass any required arguments inside the parentheses.
What are the steps to define a constructor?
- Use the
publickeyword. 2. Use the same name as the class. 3. Define parameters (if any) inside parentheses. 4. Write the constructor body to initialize instance variables.
What are the steps to define a method?
- Specify the access modifier (e.g.,
public,private). 2. Specify the return type (orvoidif no return value). 3. Give the method a name. 4. Define parameters (if any) inside parentheses. 5. Write the method body.
What are the steps to implement encapsulation?
- Declare instance variables as
private. 2. Providepublicgetter methods to access the values of the instance variables. 3. Providepublicsetter methods to modify the values of the instance variables (if needed).
What are the steps to overload a constructor?
- Create multiple constructors with the same name as the class. 2. Ensure each constructor has a different parameter list (different number or types of parameters).
What are the steps to determine instance variables?
- Identify the characteristics or attributes of the class. 2. For each characteristic, determine an appropriate data type. 3. Declare the instance variables with the chosen data types.
What are the steps to determine methods?
- Identify the actions or behaviors that objects of the class should perform. 2. Determine the inputs (parameters) required for each action. 3. Determine the output (return type) of each action. 4. Implement the methods to perform the actions.