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✔ Core Java: JDK vs. JRE vs. JVM, OOPs concepts, String immutability, Garbage Collection.
✔ Collections: HashMap internals, ArrayList vs. LinkedList, HashSet vs. TreeSet.
✔ Multithreading: Thread vs. Runnable, synchronized block, deadlock prevention.
✔ Java 8: Lambda, Streams API, Functional Interfaces, Optional class.
✔ Exception Handling: Checked vs. Unchecked, try-catch-finally, throw vs. throws.
✔ Spring Boot: Annotations, Auto-Configuration, Microservices (Eureka, API Gateway).
💡 Stay interview-ready!
Practice Verified Codes and Commands
1. JDK vs. JRE vs. JVM
<h1>Check Java version</h1> java -version <h1>Check JRE location</h1> which java <h1>Check JDK location</h1> which javac
2. String Immutability
String str = "Hello";
str.concat(" World");
System.out.println(str); // Output: Hello
3. HashMap Internals
HashMap<String, Integer> map = new HashMap<>();
map.put("one", 1);
map.put("two", 2);
System.out.println(map.get("one")); // Output: 1
4. Lambda Expressions
List<String> list = Arrays.asList("a", "b", "c");
list.forEach(element -> System.out.println(element));
5. Spring Boot Annotations
@RestController
public class MyController {
@GetMapping("/hello")
public String hello() {
return "Hello World";
}
}
What Undercode Say
Java remains one of the most robust and widely-used programming languages in the world, especially for enterprise-level applications. Understanding the core concepts like JDK, JRE, and JVM is crucial for any Java developer. The distinction between these components is fundamental, as the JDK provides the tools necessary for developing Java applications, the JRE is the environment in which they run, and the JVM is the engine that executes the bytecode.
String immutability is another critical concept in Java. Once a String object is created, it cannot be changed. This immutability leads to safer code and is a key feature in Java’s design. For example, when you concatenate strings, a new String object is created, leaving the original string unchanged.
Collections in Java, such as HashMap, ArrayList, and HashSet, are essential for data manipulation. Understanding their internals, like how HashMap uses hashing to store key-value pairs, can significantly optimize your code. Similarly, multithreading in Java allows for concurrent execution of two or more threads, which can lead to more efficient use of CPU resources. However, it also introduces complexities like deadlocks, which need to be carefully managed.
Java 8 introduced several powerful features like Lambda expressions and the Streams API, which have revolutionized the way Java code is written. Lambda expressions allow for clearer and more concise code, while the Streams API provides a powerful way to process sequences of elements.
Exception handling in Java is another area that requires careful attention. Understanding the difference between checked and unchecked exceptions, and knowing when to use try-catch-finally blocks, is crucial for writing robust applications.
Finally, Spring Boot has become the de-facto standard for building microservices in Java. Its annotations and auto-configuration capabilities make it incredibly easy to set up and run Spring applications. Understanding these features is essential for any Java developer looking to build scalable and maintainable applications.
For further reading, you can explore the official Java documentation and Spring Boot guides, which provide in-depth insights into these topics.
By mastering these concepts and tools, you can significantly enhance your Java development skills and stay ahead in the ever-evolving tech landscape.
References:
initially reported by: https://www.linkedin.com/posts/sumit-yadav-08562422b_java-activity-7300735199846260736-_3wC – Hackers Feeds
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