import java.util.Hashtable;
import java.util.Map;
public class Program
{
public static void main(String[] args) {
Map<Integer,String> hashtable=new Hashtable<Integer,String>();
hashtable.put(11,"a");
hashtable.put(null,"c");
hashtable.put(null,null);
System.out.println(hashtable.size());
System.out.println(hashtable);
}
}

import java.util.HashMap;
class Employee{
private String name;
public Employee(String name){
this.name=name;
}
public int hashCode(){
return 1;
}
}
public class Program
{
public static void main(String[] args) {
HashMap<Employee,String> hashMap=new HashMap<Employee,String>();
hashMap.put(new Employee("a"),"emp1");
hashMap.put(new Employee("b"),"emp2");
hashMap.put(new Employee("a"),"emp1 overridden");
System.out.println(hashMap.size());
System.out.println(hashMap.get(new Employee("a")));
}
}

import java.util.HashMap;
class Employee{
private String name;
public Employee(String name){
this.name=name;
}
public boolean equals(Object obj){
return true;
}
}
public class Program
{
public static void main(String[] args) {
HashMap<Employee,String> hashMap=new HashMap<Employee,String>();
hashMap.put(new Employee("a"),"emp1");
hashMap.put(new Employee("b"),"emp2");
hashMap.put(new Employee("a"),"emp1 overridden");
System.out.println(hashMap.size());
System.out.println(hashMap.get(new Employee("a")));
}
}

import java.util.HashMap;
class Employee{
private String name;
public Employee(String name){
this.name=name;
}
public int hashCode(Object obj){
return (this.name==null ? 0: this.name.hashCode());
}
}
public class Program
{
public static void main(String[] args) {
HashMap<Employee,String> hashMap=new HashMap<Employee,String>();
hashMap.put(new Employee("a"),"emp1");
hashMap.put(new Employee("b"),"emp2");
hashMap.put(new Employee("a"),"emp1 overridden");
System.out.println(hashMap.size());
System.out.println(hashMap.get(new Employee("a")));
}
}

An overview of HTTP - HTTP | MDN
https://developer.mozilla.org/en-US/docs/Web/HTTP/Overview

Polymorphism, Encapsulation, Data Abstraction and Inheritance in Object-Oriented Programming | nerd.vision
https://www.nerd.vision/post/polymorphism-encapsulation-data-abstraction-and-inheritance-in-object-oriented-programming

TOP 10 SQL Concepts for Job Interview

1. JOINs (Inner/Left/Right/Self)
2. Group By and Order By
3. Aggregate Functions (sum/avg/max/min)
4. Union and Union All
5. Date and Time processing
6. String processing
7. Window Functions (Partition by)
8. Subquery
9. View and Index
10. Common Table Expression (CTE)

SQL Join is a very important concept for any Data Science or Analytics Job Interview as well as day to day work.

Please refer to this 3 page document for understanding different SQL Join types.

Once you have understood the concepts, please go ahead and practise it with some actual or sample data tables.

(Document Credit: Steve Stedman)

I’m sure SQL will help you a lot in your Data Science journey and make you an awesome Data Scientist. All the best! 👍🏻

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Gfg courses -:
https://mega.nz/folder/ud5xgKaA#qgonl3ihVBgiWK-z9aSZRg
For gfg DSA -:
[Part 1 -> 3.Data Structures (Advanced)]
Or follow this link (works on pc)
https://mega.nz/folder/ud5xgKaA#qgonl3ihVBgiWK-z9aSZRg/folder/SNJwnCCI

import java.util.PriorityQueue;
public class Main
{
public static void main(String[] args) {
PriorityQueue<Integer> p=new PriorityQueue<Integer>();
p.add(1);
p.add(2);
p.add(3);
System.out.println(p.poll());
System.out.println(p.offer(4));
p.add(1);
p.remove(2);
System.out.println(p.peek());
System.out.println(p);
}
}