🔍 What is Java HashMap? Working Explained with Example Java HashMap is a powerful data structure from the Java Collections Framework that stores elements as key-value pairs. It allows fast access to data by leveraging hashing, making operations like insertion, lookup, and deletion highly efficient. HashMap is ideal when you need to associate unique identifiers […]
1. How do you group strings by their length? Use Java Streams to bucket strings by length. This approach is concise, readable, and leverages the Collectors API for efficient grouping in a single pass. Map grouped = list.stream() .collect(Collectors.groupingBy(String::length)); Tip: For large lists, consider parallelStream() only when the operation is CPU-bound and the stream source […]
1. How do you filter strings that start with a specific letter? List<String> names = Arrays.asList(“Alice”, “Bob”, “Amanda”, “Brian”); List<String> filtered = names.stream() .filter(name -> name.startsWith(“A”)) .collect(Collectors.toList()); 2. How do you convert a list of strings to a map with string length as key? List<String> words = Arrays.asList(“Java”, “Stream”, “Lambda”); Map<Integer, String> map = words.stream() […]
1. What is a functional interface in Java 8? A functional interface defines exactly one abstract method and serves as a target for lambda expressions and method references. It may include default or static methods for reusable behavior and can be annotated with @FunctionalInterface to communicate intent and enable compiler checks. @FunctionalInterface interface MyFunc { […]
Java interview questions with clear explanations, examples and best-practice notes These answers are expanded with concise examples, common pitfalls, and practical usage notes to increase user value, dwell time, and search relevance. Use canonical links and internal anchors when integrating into your site. 1. What is the difference between abstract classes and interfaces in Java? […]