public class Program
{
int a;
boolean isTrue;
static int i;
public static void main(String[] args) {
Program p=new Program();
System.out.println(p.a);
System.out.println(p.isTrue);
System.out.println(p.i);
}
}

import java.util.HashSet;
import java.util.Set;
public class Program
{
public static void main(String[] args) {
Set hashSet = new HashSet();
hashSet.add("1");
hashSet.add(1);
hashSet.add(null);
hashSet.add("null");
System.out.println(hashSet);
}
}

public class Program
{
public static void main(String[] args) {
Super s=new SubClass();
s.foo();
}
}
class Super{
void foo(){
System.out.println("Super class");
}
}
class SubClass extends Super{
static void foo(){
System.out.println("SubClass");
}
}

Java HashMap with Realtime Examples
http://www.javachain.com/java-hashmap-with-examples/

25 Multithreading Interview Questions (With Example Answers) | Indeed.com
https://www.indeed.com/career-advice/interviewing/multithreading-interview-questions

10 Tips to Help You Stand Out as a Java Developer | by John Selawsky | Mar, 2021 | Better Programming
https://betterprogramming.pub/10-tips-to-help-you-stand-out-as-a-java-developer-9865516584ae