If you are aspirant for a senior Java developer role, then you can go through the following Java interview questions along with answers to prepare for interview.
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What is the difference between JDK, JRE, and JVM?
- JDK (Java Development Kit): This is a comprehensive software development environment that includes everything you need to create, compile, run, and debug Java applications. It contains the Java compiler, Java Runtime Environment (JRE), and various development tools like debuggers, documentation generators, and more.
- JRE (Java Runtime Environment): This is the minimum set of components required to run Java applications. It includes the Java Virtual Machine (JVM) and the class libraries that provide the core functionality of the Java platform.
- JVM (Java Virtual Machine): This is a software program that interprets and executes Java bytecode. It acts as a layer of abstraction between the Java code and the underlying hardware, making Java platform-independent.
In essence, the JDK is a superset of the JRE. To develop Java applications, we need the JDK. If we only just want to run Java applications, you need the JRE. And both the JDK and JRE rely on the JVM to execute Java code.
Explain the concept of garbage collection in Java.
Garbage collection is the automatic process of memory management in Java. The JVM identifies objects that are no longer in use and reclaims their memory.
What are the different types of garbage collectors in Java?
Java’s garbage collection mechanism is designed to automatically reclaim memory that is no longer in use. Over the years, different garbage collectors have been introduced to optimize performance and cater to specific use cases. Here’s a breakdown of the 3 primary types:
1. Serial Garbage Collector
- Target: Suitable for single-threaded applications or environments with limited resources.
- How it works: The serial collector operates in a single thread, stopping all application threads while performing garbage collection. This can be inefficient for multi-core systems.
2. Parallel Garbage Collector
- Target: Primarily used in multi-core environments.
- How it works: The parallel collector uses multiple threads to perform garbage collection, improving performance on machines with multiple processors or cores.
3. Concurrent Mark-Sweep (CMS) Garbage Collector
- Target: Designed for low-latency applications, such as web servers.
- How it works: The CMS collector attempts to minimize pauses during garbage collection by performing most of the work concurrently with the application threads. However, it might introduce a final pause for compaction.
What is the difference between == and .equals() in Java?
== compares object references, while .equals() compares object contents.
Explain the concept of method overloading and method overriding in Java.
Method overloading: In a single Java class, there can be multiple methods with the same name but different parameters. This is called Method Overloading. Method overloading increases the readability of the program.
Method overriding: In this process, a subclass provides a specific implementation of a method inherited from its superclass. The method name, parameter and return types must be exactly same in subclass as in superclass.
What are lambda expressions and how do they simplify code in Java 8?
Lambda expressions are anonymous block of codes i.e. they are similar to a method without a name but can take parameters, process it based on expressions. Lambda is introduced in Java 8. Lambdas help us disassociate a set of instruction from object.
What is the purpose of the Stream API in Java 8?
The Stream API provides a declarative way to process collections of data. It supports functional-style operations like filtering, mapping, and reducing.
Explain the concept of method references in Java 8.
Method references provide a concise way to refer to methods without explicitly defining a lambda expression. This is a new feature introduced in Java 8 which has reduced the lines of code.
What is the difference between default and static methods in interfaces?
Default methods: Default methods are introduced in Java 8. Unlike prior versions of Java, they provide a default implementation for methods in interfaces.
Static methods: Static methods can be directly invoked on the interface itself, without creating an instance.
What is the purpose of the Optional class in Java 8?
The Optional class represents a container that may or may not contain a non-null value. It helps in handling null values gracefully and avoiding NullPointerExceptions.