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What are the differences between a constructor and a method?
Constructor: Initializes objects, has the same name as the class, no return type. | Method: Performs actions, can have any name, has a return type (or void).
What are the differences between public and private access modifiers?
Public: Accessible from anywhere. | Private: Accessible only within the class.
What are the differences between instance variables and local variables?
Instance variables: Declared within a class, outside any method, accessible by all methods in the class. | Local variables: Declared within a method, accessible only within that method.
What are the differences between getter and setter methods?
Getter: Accesses the value of an instance variable. | Setter: Modifies the value of an instance variable.
What are the differences between a class and an object?
Class: A blueprint or template. | Object: An instance of a class.
What are the differences between a default constructor and a parameterized constructor?
Default constructor: No parameters, provides default values. | Parameterized constructor: Takes parameters, allows custom initialization.
What are the differences between a method with a return type and a method with a void return type?
Return type: Returns a value of the specified type. | Void: Does not return any value.
What are the differences between a class header and a class body?
Class header: Specifies the class name and visibility. | Class body: Contains variable declarations and methods.
What are the differences between creating a new object and using an existing object?
Creating a new object: Allocates new memory and initializes the object. | Using an existing object: Operates on an object that has already been created.
What are the differences between calling a getter method and directly accessing a public instance variable?
Getter method: Provides controlled access and allows additional logic. | Public instance variable: Direct access, no control or additional logic.
What are the general steps to writing a class in Java?
1. 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?
1. Declare a variable of the class type. 2. Use the `new` keyword 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?
1. 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.variableName` or `objectName.getVariableName()`).
What are the steps to call a method on an object?
1. 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?
1. Use the `public` keyword. 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?
1. Specify the access modifier (e.g., `public`, `private`). 2. Specify the return type (or `void` if 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?
1. Declare instance variables as `private`. 2. Provide `public` getter methods to access the values of the instance variables. 3. Provide `public` setter methods to modify the values of the instance variables (if needed).
What are the steps to overload a constructor?
1. 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?
1. 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?
1. 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.
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;
}
```