“Core Java” is Sun’s term, used to refer to Java SE, the standard edition and a set of related technologies, like the Java VM, CORBA, etc. This is mostly to differentiate from others like Java ME or Java EE. “Core Java” is Oracle’s definition and refers to subset of Java SE technologies.
The Core Java technologies and application programming interfaces (APIs) are the foundation of the Java Platform, Standard Edition (Java SE). They are used in all classes of Java programming, from desktop applications to Java EE applications.
In Java, all types of enumerations and iterators (such as Iterator, ListIterator, SplitIterator) are simply navigational cursors and the main purpose of these cursors is to iterate over the elements of the collection. Each cursor has its own features, advantages and disadvantages. In this article, we will walk through these …
Java ArrayList is part of the collection framework and implementation of resizable array data structure. Learn when to use array and arraylist.
Java ArrayList does not publicly expose the length of the backing array, and only the count of the stored elements can be retrieved using its size() method.
Learn to sort Java ArrayList in ascending and descending order using ArrayList.sort(), Collections.sort(), Comparator interface and Java 8 Streams.
To convert decimal to hexadecimal, divide by 16 repeatedly and read the remainders in reverse, so 269 becomes 10D. See a worked division table, a table of common conversion examples, and the Java one-liners for both directions.
Learn what is pattern, and record patterns in detail along with how they help in pattern matching for instanceof and switch statements.
Since Java 21, we can use unnamed classes and instance main methods that allow us to bootstrap a class with minimal syntax.
The new sequenced collection interfaces allow adding, retrieving, and removing elements at either end of the collection, along with a reverse-ordered view of it.
Learn the differences between Sourcepath, Classpath and Buildpath and how they contribute to an application’s development, build and deployment phases.
This article discusses the new developer features in Java 21 including Virtual Threads, Unnamed classes, Sequenced Collections and Record Patterns.
Learn to fix the selenium WebDriver error “This version of ChromeDriver only supports Chrome version” during UI testing.
The Map.computeIfAbsent() method computes the mapped value for a key using a mapping function if the specified key does not exist in the Map or is mapped to a null value. It has been added as the default method in the Map interface in Java 8. 1. When to Use the computeIfAbsent() …
This Java tutorial discusses string templates in Java which is a new addition to the language in Java 21 as a preview feature.
Learn the Java ConcurrentSkipListMap and the major differences between ConcurrentSkipListMap and other Map implementations.
The OutOfMemoryError is a common issue in Java applications, occurring when the JVM cannot allocate enough memory to fulfill a request.
JWT tokens are commonly used in authentication and authorization processes to prove a user’s identity or grant access to specific protected resources.
JPAstreamer helps in fetching and processing the JPA or hibernate entities in the same way as we process the POJOs using Java 8 Stream API.
Learn to solve the Java compiler exception “Java class file has wrong version” while migrating an application to Spring 6 or Spring boot 3.
In Java, the volatile variables should be utilized when all changes made to a variable by one thread are immediately visible to other threads.
In Java, local variables are thread-safe because they are stored on the stack memory, which is a unique space allocated to each thread when it is created.
Learn to convert an array of primitives (int, long, float, double) to a List in Java using the iteration, Streams and open-source libraries.
Learn to handle the checked exceptions thrown from the methods used in Stream operations in Java 8 using safe method extraction and Optional.
Learn Java ZoneId and ZoneOffset with examples. Create zones with ZoneId.of(), list all zone IDs, convert a ZoneId to a ZoneOffset at an instant, handle ZoneRulesException and use ZoneId.SHORT_IDS.
Learn to generate random numbers (ints, floats) in a range using new methods added in Java 8 in Random, SecureRandom and ThreadLocalRandom.
Learn to convert a specified Instant (in UTC) to ZonedDateTime (at some zone), and ZonedDateTime to Instant with easy-to-follow Java examples.
Learn to convert a given Instant to LocalDateTime, LocalDate, or LocalTime instances in the current system timezone or a specified timezone in Java. 1. Difference between Instant and LocalDateTime An Instant is an instantaneous point on the time-line without any timezone information associated with it. Internally, it uses the system …
Learn to convert a specified array of strings to an array of int or Integer values using Java 8 Streams and learn to handle invalid values.
The JMH error “Unable to find the resource: /META-INF/BenchmarkList” is mostly observed when we do not configure the compiler plugin.
Learn to mask a string or number with a mask character except the last 4 characters at the end, e.g., in account numbers and SSN.
Learn about Java Runnable and Callable Interfaces with simple examples and some of the main usages and differences between both interfaces.
Learn to implement the builder pattern style fluent API and copy constructors in Java records for creating immutable records with examples.
Learn what is a daemon thread in Java, how to create a daemon thread, and various methods present for daemon threads in the Thread class.
Learn to configure ‘Delete’ action with RollingFileAppender and DefaultRolloverStrategy which will delete the old logs after a certain time.
Learn to find the minimum value and the maximum value in a Map using Steam API, Collections API and simple comparison using iteration.
Comparing two Java lists with order ignored is a common requirement during JUnit tests where both lists come from different sources.
Learn to read or write a huge excel (.xlsx) files in Java using the fastexcel library, which is an excellent alternative for Apache POI.
java.lang.UnsupportedOperationException means the code tried to change a collection that cannot be changed, such as one from Arrays.asList(), List.of() or Collections.unmodifiableMap(). Copy the data into an ArrayList or HashMap to fix it.
Learn about Java ArrayDeque and its features with practical examples. Learn to use it as Stack and Queue, and the difference from LinkedList.
Java Microbenchmark Harness (JMH) is a tool that allows measuring various code performance characteristics and identifying bottlenecks with precision – up to the method level.
Java has 51 reserved words and 16 contextual keywords that cannot be used as identifiers in the code. Programmers should not use these keywords for other purposes.
Java IO is a collection of APIs targeted at reading and writing data from various sources to several targets. For example, we can read data from a file or over a network, write to a file or write a response back over the network. This page categorizes the various IO-related common tasks …
Java SynchronousQueue is a specific type of BlockingQueue with no internal capacity and is primarily used in exchanging data between two threads.
Learn Queue data structure and the Java Queue interface and implementations with practical examples such as LinkedList, PriorityQueue and ArrayDeque.
Learn about the new features and changes introduced in Spring 6 and Spring boot 3 such as baseline upgrade to Java 17 and removing all deprecated classes, methods and properties.
Java String class examples. Learn to create strings, methods, comparisons, formatting and various conversions with simple and easy to follow Java examples.
Learn to find a file by name in a given directory and its sub-directories in Java and search up to a configured depth of sub-directories with examples.
Collectors.groupingBy() groups a Java stream into a Map by a key and aggregates each group with a downstream collector such as counting(), summingInt() or maxBy(). Examples for multi-level grouping, TreeMap order, sorting by value and partitioningBy.
Learn to convert Map keys and values to the array, List or Set using the ArrayList and HashSet constructors as well as Stream APIs.
Learned the root cause and solution of the Java Stream exception “IllegalStateException: stream has already been operated upon or closed”.
Learn InterruptedException and when it is thrown with examples. We will also see how we can handle this exception in our code.
HowToDoInJava provides tutorials and how-to guides on Java and related technologies.
It also shares the best practices, algorithms & solutions and frequently asked interview questions.