A curated collection of production-ready Java snippets that I use for interviews, DSA, backend development, Spring Boot projects, and day-to-day problem solving.
Java quick reference
Java snippets
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10 snippets organized across 9 categories, ready to browse whenever you need them.
A quick snapshot of the Java snippet collection, organized into practical categories for interviews, backend development, and everyday coding.
10
Java snippets
9
Categories
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Featured
Java
Language
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Every snippet is grouped into a category — bigger chips mean more snippets are available.
Hand-picked snippets that I frequently use in interviews, competitive programming, and backend development.
Java Library
Browse every Java snippet in one place. From arrays and strings to Streams API, Spring Boot and Collections, everything is organized for quick learning and faster development.
This snippet demonstrates how to reverse an array efficiently using the two-pointer technique. It swaps elements from both ends of the array until the pointers meet in the middle. This approach is memory-efficient because it performs the reversal in place without requiring an additional array.
This snippet demonstrates how to rotate an array to the right by K positions using the reverse algorithm. Instead of shifting elements one by one, it reverses the entire array, then reverses the first K elements and finally the remaining elements. This approach is optimal and widely used in coding interviews due to its O(n) time complexity and O(1) extra space.
This snippet checks whether a given string is a palindrome using the two-pointer technique. It compares characters from both ends of the string while moving toward the center. If all corresponding characters match, the string is a palindrome; otherwise, it is not. This approach is simple, efficient, and commonly asked in coding interviews.
This snippet demonstrates how to count the frequency of each character in a string using Java's HashMap. It iterates through every character, updates its count, and finally prints the frequency of each character. This technique is widely used in string manipulation, anagram checking, and text-processing problems during coding interviews.
This snippet demonstrates how to remove duplicate elements from an ArrayList while preserving the insertion order using LinkedHashSet. It is a clean and efficient approach that combines the uniqueness of a Set with the ordered nature of a List. This technique is frequently used in Java applications for data cleaning and interview coding questions.
This snippet demonstrates two common ways to sort custom objects in Java: using the Comparable interface for natural ordering and the Comparator interface for custom sorting. Comparable is ideal when a class has a default sorting order, while Comparator provides flexibility to sort objects based on different fields. This is one of the most frequently asked Java interview concepts.
This snippet demonstrates how to perform a Depth-First Search (DFS) traversal on a binary tree using recursion. It uses the Inorder Traversal technique, where the left subtree is visited first, followed by the root node, and then the right subtree. DFS is a fundamental tree traversal algorithm used in binary trees, binary search trees, expression trees, and many interview problems.
This snippet demonstrates how to perform a Breadth-First Search (BFS) traversal on a graph using a Queue. BFS explores all neighboring nodes level by level before moving to the next level, making it ideal for finding the shortest path in unweighted graphs, level-order traversal, and connectivity problems. It is one of the most frequently asked graph algorithms in coding interviews.
This snippet demonstrates how to use Java Streams to filter and transform collections efficiently. The filter() method selects elements based on a condition, while the map() method transforms each element into a new value. Streams provide a clean, functional programming style that improves readability and reduces boilerplate code. This is one of the most important Java 8+ features and is frequently asked in Java interviews.
This snippet demonstrates how to create a simple REST API using Spring Boot. It showcases the use of the @RestController annotation, request mapping, path variables, and HTTP GET endpoints. REST Controllers are the foundation of modern backend development and are widely used for building scalable web services and APIs. This is one of the most frequently asked Spring Boot interview topics for Java backend developers.
Every snippet here represents practical Java knowledge collected from interview preparation, backend development, competitive programming, and real-world projects.
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