50+ Java Collections and Generics Interview Questions with Answers

Hello guys, If you are preparing for Java interviews then you may know that Java Generics and Collections are two of the most important topics, particularly Generics where some of the trickiest Java questions can be asked. They are also used to gauge your experience and depth of your Java knowledge, hence it's imperative for both beginners and experienced Java programmers to prepare this topic well. While the Java Collection framework provides an implementation of some command data structures like List, Set, Array, Hash table, Queue, Stack, PriorityQueue, etc, Generics provides Type safety.

How to sort a Map by keys in Java 8 - Example Tutorial

In the last article, I have shown you how to sort a Map by values in Java 8, and in this tutorial, you will learn how to sort a Map by keys like a HashMap, ConcurrentHashMap, LinkedHashmap, or even Hashtable. Theoretically, you cannot sort a Map because it doesn't provide any ordering guarantee. For example, when you iterate over a HashMap, you don't know in which order entries will be traversed because HashMap doesn't provide any ordering. Then, how can you sort a Map which doesn't support order? Well, you can't and that's why you only sort entries of HashMap but you don't store the result back into HasMap or any other Map which doesn't support ordering. If you do so, then sorting will be lost.

How to use TreeSet in Java? SortedSet Example Tutorial

Hello friends, we meet again for our journey of learning Java. Today, we are gonna learn something very fruitful and easy. Hope you all are excited and ready. I would recommend you guys to go through the HashSet article which goes over hashing and what sets are actually as this topic has some of its features. So, What's the wait? Let's start! Continuing our example used in HashSet and reusing it here. Suppose you guys are given the task of storing car names (yes, I love cars :p). Now, how would you store it? This question has already been answered by our HashSet article. The new problem here is, we need to store the names in a naturally sorted manner. As we have a set of String, we need to sort them alphabetically. How to do that?

Difference between Stack and Queue Data Structure in Java? Example

Stack and Queue are two of the important data structures in the programming world and have a variety of usage. As opposed to the array and linked list, which are considered primary data structures, they are secondary data structures that can build using an array or linked list. You can use Stack to solve recursive problems and Queue can be used for ordered processing. The difference between Stack and Queue Data structure is also one of the common questions not only in Java interviews but also in C, C++, and other programming job interviews.

How to remove all elements (empty) from ArrayList in Java? Clear vs RemoveAll Example Tutorial

Many times we want to reset an ArrayList for the reusing purpose, by resetting we mean clearing it or removing all elements. There are two ways to reset an ArrayList in Java, by using the clear() method or calling removeAll(). If your ArrayList is small enough like it contains only 10 or 100 elements then you can use any of these two methods without worrying too much, but, if you have a huge list of lots of objects like an ArrayList containing 10M entries, then the choice of clear() vs removeAll() can make a huge difference in the performance of your Java application.

3 Ways to Convert an Array to ArrayList in Java? Example

How to convert an Array to ArrayList in Java
Have you encountered any situation where you quickly wanted to convert your array to ArrayList or ArrayList to array in Java? I have faced many such situations that motivate me to write these quick Java tips about converting an array to ArrayList and ArrayList to array in Java. Both array and ArrayList are quite common and every Java developer is familiar with this. Former is used to store objects and primitive types while later can only hold objects. The array is part of standard Java fundamental data structure while ArrayList is part of the collection framework in Java.

HashSet in Java – 10 Examples Programs Tutorial

HashSet in Java is a collection that implements the Set interface and is backed by a HashMap. Since HashSet uses HashMap internally it provides constant-time performance for operations like add, remove, contains and size give HashMap has distributed elements properly among the buckets. Java HashSet does not guarantee any insertion orders of the set but it allows null elements. HashSet can be used in place of ArrayList to store the object if you require no duplicate and don't care about insertion order.