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00: Top 50+ Core Java interview questions & answers for 1 to 3 years experience

Top 50 core Java interview questions covering core Java concepts with diagrams, code, examples, and scenarios. If you don’t get these Java interview questions right, you will not be getting an offer.

== Vs equals(…)

Q1. What is the difference between “==” and “equals(…)” in comparing Java String objects?
A1. When you use “==” (i.e. shallow comparison), you are actually comparing the two object references to see if they point to the same object. When you use “equals(…)”, which is a “deep comparison” that compares the actual string values. For example:

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00: Top 50+ Core Java interview questions answered – Q11 to Q23

The focus is on Java OOP interview questions and answers. Q11. What is the difference between constructors and other regular methods? A11. Constructors must have the same name as the class name and cannot return a value. The constructors are called only once per creation of an object while regular…

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00: Top 50+ Core Java interview questions answered – Q24 to Q36

Focus is on Java classes, interfaces and generics the interview questions and answers style. Java classes and interfaces are the building blocks. Q24. What happens when a parent and a child class have the same variable name? A24. When both a parent class and its subclass have a field with…

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00: Top 50+ Core Java interview questions answered – Q37 to Q42

As a Java developer, you may not need to know how the JVM works, but the most important topic that you must know is Java Garbage Collection. How the Garbage Collection and object referencing work in Java. Q37. What do you know about the Java garbage collector? When does the…

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00: Top 50+ Core Java Interview questions answered – Q43 to Q54

Q43. What can you tell about the performance of a HashMap compared to a TreeMap? Which one would you prefer? A43. A balanced tree does have O (log n) performance. The TreeMap class in Java maintains key/value objects in a sorted order by using a red-black tree. A red-black tree…

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01: 15+ Java multithreading interview questions & answers

Multithreading is one of the important features of Java, and multithreading interview Q&As can reveal a lot about your depth of core Java knowledge. Most importantly, it is not easy to grasp multithreading concepts without lots of hands-on experience. Let’s start with the beginner basics & then get into Java concurrency management interview Q&As for the experienced.

What is a thread?

Q1. What is a thread?
A1. It is a thread of execution in a program. The JVM (i.e. process) allows an application to have multiple threads of execution running concurrently. In the Hotspot JVM there is a direct mapping between a Java Thread and a native operating system (i.e. OS) Thread. When a thread terminates, all resources for both the native and Java thread are released.

Q2. What are the JVM created threads?
A2. The main thread and a number of background threads.

1) main thread, which is created as part of invoking the main(…) method

2) VM background thread to perform major GC (i.e. Garbage Collection), thread dumps (e.g. kill -QUIT in Unix), thread suspension, etc.… Read more ...

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02: 10 Java String class interview Q&As

Java Collection interview questions and answers and Java String class interview questions and answers are must know for any Java developer as these two APIs are the most frequently used in your Java application code. You can’t write any decent Java application without these 2 APIs. Q1. What will be…

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02: 5 Java multithreading scenarios interview Questions & Answers

Java interview questions & answers on multithreading scenarios to judge your experience in building applications with concurrency in mind. Q1. Can you give some scenarios where you built concurrent systems? A1. In a concurrent system different threads run concurrently, whereas in a distributed system different processes often in separate machines…

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03: 7 Things you must know about Java locks and synchronized key word

7 Things you must know about Java locks and synchronized key word summarizes the key basics. #1. Each Java class and object (i.e. instance of a class) has an intrinsic lock or monitor. Don’t confuse this with explicit lock utility class that were added in Java 1.5, and I will…

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03: Understanding Big O notations with Java

Q1.  Have  you seen job advertisements requiring Java candidates to work in real-time or high volume transaction processing systems? A1.  If you are applying for such jobs, you can be quizzed on Big O notation. Here are some basics to brush up on. Big O gives you the upper bound. For example,…

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