Difference between instance and Object in Java

Difference between instance and Object in Java

In Java or other object oriented programming language, we often use Object and instance word interchangeably, but sometimes it confuses beginners like hell. I have been often asked several times, whether object and instance are the same thing or different? Why we sometimes use object and sometimes instance if they are same thing etc? This gives me the idea to write a little bit about it. I will mostly talk about Java conventions perspective. Just like we use word function in C or C++  for a block of code, which can be called by its same, but in Java, we refer them as methods. In Java functions are known as methods, similarly, objects are known as instances in Java. You have a class, which represent a blueprint of a real world thing e.g. Car, and object represents a real world car e.g. your car, my car, a red car or a blue car. They are also known as instances of the car.

Difference between Iterator and ListIterator in Java

Difference between Iterator and ListIterator in Java?

The Iterator is the standard way to traverse a collection in Java. You can use Iterator to traverse a List, Set, Map, Stack, Queue or any Collection, but you might not know that there is another way to traverse over List in Java? Yes, it's called the ListIterator. There are many differences between Iterator and ListIterator in Java, but the most significant of them is that Iterator only allows you to traverse in one direction i.e. forward, you have just got a next() method to get the next element, there is no previous() method to get the previous element. On the other hand, ListIterator allows you to traverse the list in both directions i.e. forward and backward. It has got both next()and previous() method to access the next and previous element from List.

Difference between Heap and Stack Memory in Java JVM

Difference between Heap and Stack Memory in Java JVM

One of the many traits of a good programmer is how well he understands the fundamental and if you want to check the fundamentals of Java programmer than asking the difference between heap and stack memory is a good choice. Even though both are part of JVM and both consumers memory allocated to the Java process, there are many differences between them e.g. Heap memory is shared by all threads of Java application but Stack memory is local to each thread. Objects are created in heap memory but method frames are stored in Stack memory, and size of heap space is much bigger than the small size of Stack in Java. Even if you know this much information about heap and stack in Java, you are one of the better candidates, but let's see some more details to impress the interviewer.

Difference between StringBuffer, StringBuilder and String in Java

Difference between StringBuffer, StringBuilder and String in Java

Though all three classes StringBuffer, StringBuilder and String are used for representing text data in Java there are some significant differences between them. One of the most notable differences between StringBuilder, StringBuffer, and String in Java is that both StringBuffer and StrinBuilder are Mutable class but String is Immutable in Java. What this means is, you can add, remove or replace characters from StringBuffer and StringBuilder object but any change on String object e.g. converting uppercase to lowercase or appending a new character using String concatenation will always result in a new String object. Another key difference between them is that both StringBuffer and String are thread-safe but StringBuilder is not thread-safe in Java. String achieves its thread-safety from Immutability but StringBuffer achieves it via synchronization, which is also the main difference between the StringBuffer and StringBuilder in Java.

Difference between synchronized ArrayList and CopyOnWriteArrayList in Java?

Difference between synchronized ArrayList and CopyOnWriteArrayList in Java?

Though both synchronized ArrayList and CopyOnWriteArrayList provides you thread-safety and you can use both of them when your list is shared between multiple threads, there is a subtle difference between them, Synchronized ArrayList is a synchronized collection while CopyOnWriteArrayList is a concurrent collection. What does this mean? It means is that CopyOnWriteArrayList is designed keeping concurrency in mind and it is more scalable than synchronized ArrayList if the list is primarily used for reading. You know that ArrayList is not synchronized, so you cannot directly use it in a multi-threaded environment where you list is accessed and modified by multiple threads. In order to use ArrayList in such environment, you need to first get a synchronized list by calling Collections.synchronizedList().