There is Constructor Over Loading.

class Car{
        int price; // 0
        String name; // null
        Car(){ // default constructor

        }

        Car(int p, String s){ // Parameter constructor
            price = p;
            name = s;
        }

        Car(String s, int x){
            price = x;
            name = s;
        }

        void print(){
            System.out.println(price+" "+name);
        }
        
    }

public class Constructor_Over_Loading_In_OOP {

    public static void main(String[] args) {
        Car c1 = new Car(1250000,"Kia Sonet");
        Car c2 = new Car("Lord Alto",400000);
        Car c3 = new Car();
        c3.price = 123000;
        c3.name = "Honda Amaze";
        c1.print();
        c2.print();
        c3.print();

    }
   
}

We are inheriting parent class to child class.

// Parent class
class Animal {
    void eat() {
        System.out.println("This animal eats food");
    }
}

// Child class
class Dog extends Animal {
    void bark() {
        System.out.println("Dog is barking");
    }
}

// Main class
public class Inherit_Parent_Class_To_Child_Class_In_OOP {
    public static void main(String[] args) {
        Dog d = new Dog();

        d.eat();   // inherited method
        d.bark();  // own method
    }
}

There are some Member Of Class With Static Keyword.

class Cricketer{
    static String country = "NZ";
    int runs;
    String name;
    double avg;
    void print(){
        System.out.println(runs+" "+name+" "+avg);
    }
    
}

public class Member_Of_Class_With_Static_Keyword_In_OOP {

    public static void main(String[] args) {
       Cricketer c1 = new Cricketer();
       Cricketer c2 = new Cricketer();
       c1.country = "India";
       System.out.println(c2.country);

    }
   
}

We are passing array to constructor.

import java.util.Arrays;

class StudentData{
        String name;
        int rno;
        int[] marks;
        StudentData(int[] s){
            marks = Arrays.copyOf(s,s.length);
        }
        StudentData(int s){
            marks = new int[s];
        }
}

public class Pass_Array_To_Constructor_In_OOP {

    public static void main(String[] args) {
        int[] arr = {4,7,1,4,8};
        StudentData s1 = new StudentData(arr);
        s1.marks[0] = 40;
        System.out.println(arr[0]);
        System.out.println(s1.marks[0]);
        StudentData s2 = new StudentData(2);

    }
   
}

There is PolyMorphism Concept.

public class PolyMorphism_Concept_In_OOP {

    public static class Dog{
        void speak(){
            System.out.println("Bhau Bhau");
        }
    }
    public static class Cat{
        void speak(){
            System.out.println("Meow Meow");
        }
    }
    public static class Lion{
        void speak(){
            System.out.println("GRRRRRR");
        }
    }
    public static class Pikachu{
        void speak(){
            System.out.println("Pika Pika");
        }
    }
    public static class Human{
        void speak(){
            System.out.println("Hello");
        }
    }

    public static void main(String[] args) {
        Dog tommy = new Dog();
        Cat c = new Cat();
        Human bishal = new Human();
        Pikachu p = new Pikachu();

        tommy.speak();
        c.speak();
        p.speak();
        bishal.speak();

    }
   
}