Java OOP

Class Object Class is a template or a blueprint for object creation. The object is an instance of a class. The class does not allocate any memory when created. The object is allocated memory when created. The class is a logical entity. The object is a physical entity. Class is declared using a class keyword.…

class Vehicle { // … } class Car extends Vehicle { // … } class Test { public static void main(String[] args) { Vehicle vehicle = new Vehicle(); Car car = new Car(); System.out.println(vehicle instanceof Object); System.out.println(car instanceof Vehicle); System.out.println(car instanceof Car); } } Output: true true true   As you can see, the Vehicle…

public class Student { private String name; public String getName() { return name; } public void setName(String name) { this.name = name } } class Test { public static void main(String[] args) { Student s = new Student(); // System.out.println(s.name); // DOES NOT COMPILE s.setName(“John”); System.out.println(s.getName()); } } Output: John   If we try to…

// declaration of variables without modifiers String s = “Hello World!”; int i = 5; // method without a modifier, it can be accessed at the package level int sum(int a, int b){ return a + b; } public class Car { // private fields private String color; private int speed; // … } public…

package vehicle; public class Car { // fields and methods } package vehicle; // OK public class Car { package vehicle; // DOES NOT COMPILE // fields and methods } package vehicle; // DOES NOT COMPILE package vehicle; class Car { public void printRandomNumber() { Random r = new Random(); // DOES NOT COMPILE System.out.println(r.nextInt(10));…

Before Java 8, there were many more differences between interfaces and abstract classes, but with the introduction of default, non-abstract, and static methods in interfaces, the difference has narrowed significantly. See what still stands as the difference between these two types: Abstract Class Interface Methods Can have final methods but can not have default methods.…

interface Runnable {} interface Vehicle { void move(); } class Car implements Vehicle { @Override public void move() { System.out.println(“The car is moving…”); } } class Test { public static void main(String[] args) { Vehicle car = new Car(); car.move(); } } Output: The car is moving… interface Vehicle { void move(); } class Test…

class Vehicle { // … } class Car extends Vehicle { // … } class Test { public static void main(String[] args){ Car car = new Car(); System.out.println(car instanceof Car); System.out.println(car instanceof Vehicle); } } Output: true true   The above example shows that an object of subclass type is also a superclass type. The instanceof operator works…

class Vehicle { public void move() { System.out.println(“The vehicle is moving…”); } } class Car extends Vehicle { public void move() { System.out.println(“The car is moving…”); } } class Test { public static void main(String[] args) { //variable of type Vehicle points to the object of its subclass Car Vehicle car = new Car(); car.move();…

class Vehicle { public void start() { System.out.println(“The vehicle is started…”); } } class Car extends Vehicle { public void start() { System.out.println(“The car is started…”); } } public class Test { public static void main(String[] args) { Vehicle vehicle = new Vehicle(); Vehicle car = new Car(); vehicle.start(); car.start(); } } Output: The vehicle…

final class Vehicle { } class Car extends Vehicle { // DOES NOT COMPILE } class Vehicle { public final void methodA() { // … } } class Car extends Vehicle { public void methodA() { // DOES NOT COMPILE // … } } class Car { private final int maxSpeed = 300; public void…

class Vehicle { static { System.out.println(“Static Initializer Block…”); } } 1 class Car { 2 3 private static int one; 4 private static final int two; 5 private static final int three = 3; 6 private static final int four; // DOES NOT COMPILE 7 8 static { 9 one = 1; 10 two =…

public static void main(String[] args) { { System.out.println(“Summer”); } } { System.out.println(“Winter”); } 1 public class Car { 2 private String model = “Ford”; 3 4 { 5 System.out.println(“Instance Initializer block…”); 6 } 7 8 public Car () { 9 model = “Opel”; 10 System.out.println(“Constructor…”); 11 } 12 13 public static void main(String[] args) {…