someone might question that why do we need another article about string in Java, haven't we had enough about the string is already written? Yes, I agree there are a lot of articles related to Java string covering topics like how to use Java String, an example of Java string and almost everything you can do with string in Java. But, I wanted to document my experience of using String in Java and some nasty and little-known things I discovered about the Java String class, which may not be obvious to many Java developers. A string is available in almost every programming language and its probably the most used data structure or a data type, hence a good knowledge of String is very important for every Java developers.

# 50+ Basic Core Java Interview Questions with Hints and Answers

If you are preparing for your next Core Java interview and looking for some common question to practice or check your knowledge, then you have come to the right place. In this article, I'll share 50 Core Java Interview Questions from various companies. I have already discussed the answers to these questions in this blog or Javarevisited, so I have just put the link. First, you should try to answer it yourself and if you cannot then go to the link and find the answer. You can also compare your answer with mine and learn a few things here and there. In most of my interview post, I have also shared some common techniques to drive interview towards your comfort zone and how to leave a long-lasting impression on the interviewer, you can use those techniques to do well on your Java interviews.

# How to print all leaf nodes of a Binary Tree in Java without Recursion

In the last article, you have learned

**how to print all leaf nodes of a binary tree in Java**by using Recursion, a useful technique to solve binary tree problems and in this article, we'll answer the same question without using Recursion. Why should we do this? Well, it's a typical pattern on a programming job interview to solve the same problem using both Recursion and Iteration. Since some questions are easy to solve using recursion like linked list problems, binary tree-based problems, tower of Hanoi, or Fibonacci series but their non-recursive solution is comparatively tricky, interviewer test candidates against this shift in the algorithm.# How to implement PreOrder traversal of Binary Tree in Java - Example Tutorial

The easiest way to implement the preOrder traversal of a binary tree in Java is by using

*recursion*. The recursive solution is hardly 3 to 4 lines of code and exactly mimic the steps, but before that, let's revise some basics about a binary tree and preorder traversal. Unlike array and linked list which have just one way to traverse, I mean linearly, binary tree has several ways to traverse all nodes because of its hierarchical nature like level order, preorder, postorder and in order. Tree traversal algorithms are mainly divided into two categories, the depth-first algorithms, and breadth-first algorithms. In depth-first, you go deeper into a tree before visiting the sibling node, for example, you go deep following the left node before you come back and traverse the right node.# Top 50 Java Generics and Collection Interview Questions

Java Collection and Generic are a very important topic for Java Interviews. They also present some of the hardest questions to a programmer when it comes to interviews, especially Generics. It's not easy to first understand what a particular piece of code doing with those question mark and other signs and then the pressure of interviews also makes it hard to answer complex usage of Generics. But, with proper preparation and paying attention to both Java Collection and Generic, you can solve that hurdle. If you are looking for Java job but hasn't done well in the interviews you have given so far then you have come to the right place. In this blog, I have shared a lot of Java interview questions on various topics and difficulty levels.

# How to declare and Initialize two dimensional Array in Java with Example

An array of more than one dimension is known as a multi-dimensional array. Two of the most common examples of multi-dimensional arrays are two and three-dimensional array, known as 2D and 3D array, anything above is rare. I have never seen 4-dimensional arrays, even 3D arrays are not that common. Now the question comes when do use a multi-dimensional array? Any real-life example? Well, 2D arrays are very common on platform games like Super Mario Bros to represent screen or terrain; 2D arrays can also be used to represent structures like a spreadsheet, or to draw board games like Chess, which requires 8x8 board, Checkers and Tic-Tac-Toe, which requires 3 rows and 3 columns.

# How to find Nth Fibonacci Number in Java - Coding Problem with Solution

It's been a long time since I have discussed a coding problem in this blog. So, I am going to start with the probably the oldest one of them, how do you find the nth number in a Fibonacci sequence? or how do you find the Fibonacci number in Java? or maybe printing the Fibonacci series. If you are a regular reader of this blog then you might know that I have already discussed both recursive and iterative algorithm for printing Fibonacci series but never really discussed especially writing a program to return the

**Nth Fibonacci number**in Java. Don't worry the wait is over as in this article, we'll solve this common problem and learn a bit more about problem-solving, recursion, iteration and some basic algorithm skills.# Difference between OCAJP7, OCAJP8, and OCAJP11 Certification - 1Z0-803 vs 1Z0-808 vs 1Z0-815

One of the frequently asked questions asked by most of the OCAJP certification candidates is,

**what are the differences between OCAJP 8 and OCAJP 7?**And, after Java 11 certification release, what is the difference between OCAJP 11 (1Z0-815) and OCAJP 8 (1Z0-808) Which one Java developers should go for? OCAJP7 or OCAJP8, or OCAJP 11? The obvious answer to this question is the latest Java version of the exam, I mean OCAJP 11. Since it's already more than a couple of months since Java 12 is out but there is no OCAJP 9 certification, the OCAJP 8 should be the exam, Java developer should pursue this year and beyond. The question is more for those who are looking to become certified Java developer in quick time and doesn't know Java 8 yet like experienced Java developers who have extensively worked in Java SE 6 and prior version but don't have any Java certification yet.# Java - Variable and Method Hiding Example

If Java, if you are not careful you can possibly

*hide*both methods and variables of the superclass. A field or variable is said to hide all fields with the same name in superclasses. Similarly, a static method with the same name in a subclass can hide the method of the superclass. This can lead to subtle bugs, especially if you are expecting a different method to be called. In this article, I'll show you examples of both variable and method hiding in Java so that you can understand and avoid them in the future.# How to use Multiple Threads in Java - Example

Hello guys, Multithreading is one of the biggest strength of Java, which allows you to divide a task and execute faster by using more than one threads. In order to use multiple threads in Java, you need to first define the task which will be executed by those threads. In order to create those task, you can either use Runnable or Callable interface. If you are just learning Java chose the Runnable interface, it's simpler one, but if you are familiar with Java multithreading and want to leverage additional features offered by Callable like it can throw an exception and it can also return value, then go ahead and use the Callable interface. Once you have task ready, you need to create an instance of the Thread class.

# Post Order Traversal in Java Without Recursion - Example Tutorial

In the last article, I have shown you how to implement post-order traversal in a binary tree using recursion and today I am going to teach you about post order traversal without recursion. To be honest, the iterative algorithm of post-order traversal is the toughest among the iterative pre-order and in-order traversal algorithm. The process of post-order traversal remains the same but the algorithm to achieve that effect is different. Since post-order traversal is a

**depth-first algorithm**, you have to go deep before you go wide. I mean, the left subtree is visited first, followed by right subtree and finally the value of a node is printed. This is the reason why the value of root is printed last in the post-order traversal algorithm.# Binary tree InOrder traversal in Java using Recursion

The

**InOrder**traversal is one of the three popular ways to traverse a binary tree data structure, other two being the preOrder and postOrder. During the in order traversal algorithm, left subtree is explored first, followed by root, and finally nodes on right subtree. You start traversal from root then goes to left node, then again goes to left node until you reach a leaf node. At that point in time, you print the value of the node or mark it visited and moves to right subtree. Continuing the same algorithm until all nodes of the binary tree are visited. The InOrder traversal is also known as**left-node-right**or**left-root-right**traversal or**LNR**traversal algorithm.# Post order traversal Algorithms for Binary Tree in Java with example

In the last couple of articles, you have learned about pre-order and in-order tree traversal algorithms in Java and today, you will learn about the post order traversal in a binary tree. It is the toughest of all three tree traversal algorithms and programmers generally struggle to implement this when asked in a coding interview, hence it makes sense to understand and practice this algorithm before going for the interview. The

**post order traversal**is also a depth-first algorithm because you go deep before you visit other nodes on the same level. In post order traversal, you first visit the left subtree, then right subtree and finally you print the value of node or root. That's why the**value of root is always printed last on post-order traversal**. Like many tree algorithms, the easiest way to implement post-order traversal is by using recursion.# Can you join two unrelated tables in SQL? Cross Join Example

In one of the recent programming job interview, one of my readers was asked the question,

**how do you join two tables which are not related to each other?**i.e. they don't have any common column? is it possible in SQL? My reader got confused because he only knows about INNER join and OUTER join which require a key column like dept_id which is the primary key in one table like Department and foreign key in another table like Employee. He couldn't answer the question, though he did tell them about you can select data from multiple tables by typing multiple table names in from clause using a comma. What he was saying was right, but he didn't know much about it, so he couldn't explain it confidently. Lucky for him, he got the job but he emailed me asking the same question which inspired me to write this post.# How to Print all leaf Nodes of a Binary tree in Java - Coding Interview Questions

This is another interesting coding problem which is based on a binary tree and mostly asked beginner programmers. If you have some experience in solving binary tree based problems then it's rather easy to solve because, like many other binary tree algorithms, you can use recursion to print all leaf nodes of a binary tree in Java. Since the tree is a recursive data structure, you can apply the same algorithm to both the left and right subtree. In order to solve this problem, the first thing you should know is what is a leaf node because if you don't know that then you won't be able to solve the problem. Well, a leaf node is the one who's left and right child nodes are null.

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