SQL Interview Questions and Answers With Query Examples
This guide lists out a few of the most asked SQL interview questions and gives their answers such as JOINS, KEYWORDS, TRIGGERS and much more.
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Lokesh Gupta
Website: https://howtodoinjava.com
Github: https://github.com/lokeshgupta1981/
Twitter: @HowToDoInJAVA
My Articles:
Java Thread join(): Timeouts, Interrupts and join vs yield
Java thread join() waits for another thread to finish. Learn join(long), join(Duration), interrupts, deadlocks, visibility and yield() vs join().
Spring Cloud Features and Components
Learn about the Spring cloud modules that help in implementing 12-Factor design patterns in Spring cloud based microservices development.
XmlAssert: AssertJ Assertions for XMLUnit With Examples
Learn XmlAssert, the AssertJ API of XMLUnit, to check XML in Java tests by XPath, compare documents, ignore order and whitespace, and validate XSD.
XMLUnit Tutorial: Compare XML in Java Tests With Examples
Learn XMLUnit 2 to compare XML in Java tests, with identical vs similar checks, element order, whitespace, node filters and DifferenceEvaluator examples.
JSONassert Guide: Compare JSON in Java Tests With Examples
Learn JSONassert to compare JSON in Java tests, with LENIENT vs STRICT modes, arrays, failure messages, ignored fields and a REST response example.
Jackson – Ignoring Null, Empty and Absent Values
Learn to ignore the null, empty and absent values during serialization with Jackson using the @JsonInclude as well as SerializationInclusion.
Remove Docker Containers by Id, Name or Date
This docker tutorial explains the useful commands to remove a single or all running or stopped containers by id, name or date ranges.
Jackson – Custom Serializer and Deserializer
Learn to create custom Jackson serializers and deserializers, register using the SimpleModule as well as @JsonSerialize and @JsonDeserialize.
Jackson – Converting between XML and JSON
Learn to convert between JSON and XML strings using Jackson’s JsonMapper and XmlMapper using simple POJO, JsonNode and ObjectNode classes.
Jackson – Serialize and Deserialize Dates
By default, Jackson serializes the Dates in numeric format. Learn to customize the serialization and deserialization of date and time types in Java using Jackson.
Java HashMap: Complete Guide With Examples
Java HashMap guide with examples for put, get, merge, compute, iteration, keys, internals and thread safety, plus links to every HashMap how-to.
Java Concurrency Guide: Threads, Executors and Virtual Threads
Java concurrency explained for Java 25 with thread safety, a race condition fix, a timeline from Java 1.0 to 25 and all our tutorials grouped by task.
Java Collections & Arrays Tutorial
Learn the Java Collections Framework with a Java 21 hierarchy diagram, how to choose List, Set, Map and Queue classes, and links to every tutorial.
Java ArrayList Guide: Methods, Capacity, subList and Examples
Learn the Java ArrayList with tested examples for get(), size() vs capacity, subList(), ensureCapacity(), sorting, streams and Java 21 getFirst().
Java List Interface: Methods, Implementations and Examples
The Java List interface explained with examples of List.of(), positional methods, Java 21 sequenced methods and how to choose an implementation.
Java Map: HashMap vs LinkedHashMap vs TreeMap and More
A Java Map stores unique keys with one value each. Quick put/get/merge/computeIfAbsent examples, a comparison of HashMap, LinkedHashMap, TreeMap, ConcurrentHashMap, EnumMap, Hashtable and Map.of(), and all our Map tutorials grouped by topic.
Java Case-Insensitive Map: TreeMap, Commons and Spring
Create a Java case insensitive map with TreeMap and CASE_INSENSITIVE_ORDER, Commons CaseInsensitiveMap or Spring LinkedCaseInsensitiveMap, side by side.
Create and Start a Thread in Java: Runnable, Builders, Executors
Learn to create and start a thread in Java with Runnable, Thread, Thread.ofPlatform(), virtual threads, ExecutorService, ThreadFactory and priority.
Jackson – Custom Serialization and Deserialization of Booleans
Learn Jackson’s default serialization and deserialization of boolean values, and how to customize it to support other possible values.
Creating Jar with Dependencies using Maven Assembly Plugin
Learn to use the Maven assembly plugin for creating executable Jar files with dependencies, its various goals, descriptors using an example.
Java Versions and Features [Updated upto Java 22]
On this page, we will frequently list the major feature changes in the latest Java release, sequentially. Though we have tried to cover as much information as possible, if you know something we have missed below, please let me know, and we will add that information. Java 22 Features Java …
Java EnumMap with Examples: Usage, Streams and vs HashMap
Java EnumMap stores enum keys in an array by ordinal. Learn its constructors, null rules, key order, stream collectors and how it differs from HashMap.
Jayway JsonPath Tutorial: Read and Filter JSON in Java
Learn Jayway JsonPath 3 in Java with operators, filters, functions, typed reads with Jackson, missing-path options and updates, with runnable examples.
REST-assured POST Request and PUT Examples with JSON Body
REST-assured POST request examples with JSON body as String, Map, POJO or file, plus PUT and PATCH, headers, auth, response checks and extraction.
How to Marshal and Unmarshal XML with Jackson
Learn to serialize and deserialize a Java Object to/from an XML document, using Jackson XmlMapper, with simple and easy examples.
Remove Last Character from a String in Java (6 Ways)
How to remove last character from a string in Java with substring(), StringBuilder, regex and chop(), safe for null, empty strings and emoji.
REST-assured XML Request: Send and Validate XML Bodies
REST-assured XML request guide. Send XML from a String, file or JAXB object, set the charset, and validate responses with GPath, XPath and XmlPath.
REST-assured Tutorial: API Testing in Java with JUnit
REST-assured tutorial for API testing in Java with JUnit. Learn given/when/then, GPath checks, extraction, specifications, auth and schema validation.
Java Nested Map: Create, Update and Iterate a Map of Maps
Create a Java nested map with computeIfAbsent and streams, add, remove and iterate entries, read values safely, deep copy, flatten and choose alternatives.
Immutable vs Unmodifiable Map in Java: Differences and Examples
Immutable vs unmodifiable map in Java explained with Map.of(), Map.copyOf(), Collections.unmodifiableMap(), toUnmodifiableMap() and Guava ImmutableMap.
Collect Stream to Immutable List: toList vs toUnmodifiableList
Collect stream to immutable list in Java with toList() or Collectors.toUnmodifiableList(), how nulls differ, plus unmodifiable Set and Map collectors.
TreeMap vs HashMap in Java: Differences and When to Use Each
TreeMap vs HashMap in Java compared on ordering, speed, null keys, memory and key equality, with Java 25 examples and a table for picking the right map.
Guide to Cassandra with Spring Boot
Apache Cassandra is a distributed database system. This guide walks through the process of using Spring Data Cassandra with Spring Boot.
How to Kill a Thread in Java: interrupt(), Flags, Thread.stop
How to kill a thread in Java safely with interrupt() or a volatile flag, why Thread.stop() throws UnsupportedOperationException and how to stop tasks.
Apache POI: Append Rows to an Existing Excel File in Java
Append rows to an existing Excel sheet with Apache POI 5.5.1. We find the next free row, keep the date and number formats, add rows before a totals row and save through a temp file so a failed write never empties the spreadsheet.
Thread Name in Java: Set and Get the Name of a Thread
Set and get the thread name in Java with getName(), setName(), constructors and Thread builders, default names, executor thread names and threadId().
Apache POI SAX Parser: Read Large Excel Files in Java
Read large Excel files with the Apache POI SAX parser and XSSFSheetXMLHandler, handle missing cells and dates, import in batches, write with SXSSF.
Java IdentityHashMap: Reference Equality vs HashMap
Java IdentityHashMap compares keys with == instead of equals(). Learn how it differs from HashMap, the String and Integer traps and the Java 20 change.
Java ConcurrentMap: Atomic Methods and Implementations
Java ConcurrentMap with putIfAbsent, compute and merge examples, why get-then-put loses updates, null rules and ConcurrentHashMap vs ConcurrentSkipListMap.
How to Debug Java Streams: peek() and IntelliJ Stream Trace
Learn to debug Java streams with peek(), lambda breakpoints and the IntelliJ Trace Current Stream Chain action, and avoid the peek() and count() traps.
Java Wait for All Threads to Finish: 7 Ways With Examples
Java wait for all threads to finish with ExecutorService close(), invokeAll(), Future.get(), CountDownLatch, CompletableFuture.allOf() and join().
Java WeakHashMap: Weak Keys, GC Behavior and Use Cases
Learn how Java WeakHashMap removes entries after GC clears weak keys, the String and value-reference traps, WeakHashMap vs HashMap and real use cases.
Create Docker Image for Spring Boot App: Step by Step
Learn to configure and run a spring boot application into a docker container. Also learn the process step by step with proper code examples.
Ternary Operator in Java: Syntax, Examples and Pitfalls
The ternary operator in Java with examples covering syntax, result types, the null unboxing trap, nested ternaries and when to use if-else instead.
Java Structured Concurrency with StructuredTaskScope (Java 25)
Java structured concurrency with the Java 25 preview API. Learn StructuredTaskScope.open(), fork, join, Joiners, timeouts, custom joiners and the flags.
Java Virtual Threads Guide with Examples (Java 25)
Java virtual threads explained for Java 25 with examples, carrier threads, the Java 24 pinning fix, when not to use them, pooling and ThreadLocal pitfalls.
TestNG Tutorials
TestNG is a test automation framework inspired by JUnit. It can be used for unit testing, functional, integration, and end-to-end testing.
Mock Static Methods with Mockito
Learn to mock the static methods (in and outside the scope) using Mockito in unit testing in Java using MockedStatic class.
EasyMock Tutorial: Mocking with EasyMock 5 and JUnit 5
EasyMock tutorial with JUnit 5. Create mocks, record expectations, replay and verify, mock void methods, use matchers, captures and nice or strict mocks.