How to Answer Hard Interview Questions About Java (With Example Answers)
Java is one of the most popular ways to write code. During an interview for a job in software development, your employer may ask you about how well you know this framework. If you want to work in a field like application development, knowing how to answer Java interview questions could help you get a job. In this article, we’ll talk about common Java interview questions and give you advice on how to answer them.
Advanced questions for a Java job interview
There are a number of common interview questions about Java, such as:
- What keeps Java from being completely object-oriented?
- What do Java’s constructors do, and what’s the difference between a default constructor and one that takes parameters?
- How long do Java’s heap and stack memory last?
- Name some of Java’s access modifiers.
- Explain what an instance variable is.
- What makes an instance variable different from a local variable?
- What does it mean for a Java method to be “final,” and what does it mean for a class to be “final”?
- What does Java’s JIT stand for, and what does it do?
- Name two ways in which an object and a class are different.
- When comparing an interface class to an abstract class, which type supports multiple inheritance, allows only public members, and supports a single instance?
1.What keeps Java from being 100% object-oriented?
For a Java developer to use the language well, they need to know what makes it different. Your answer should show the interviewer that you know what Java is and how it works. You can say which data types are not objects and then name the other eight types to build on your answer.
“Java has eight data types that are not objects. They are char, byte, float, int, boolean, short, double, and long. Even though one of Java’s goals was to be an object-oriented language, these non-object data types keep it from being called a pure object-oriented language.
2. What do Java’s constructors do, and what’s the difference between a default constructor and one that takes parameters?
Constructors are a key part of the Java framework because they turn on Java objects. Your answer must show that you know how to use constructors and when to use them. You can explain how constructors work and what the main difference is between types and types.
“In Java, objects are set up by constructors, which are made up of blocks of code. A default constructor sets up an object’s instance variables with the default values. A parametrized constructor, on the other hand, sets up an object’s instance variables with the values I give. If I don’t define my constructor and set its values, when I make an object, a default constructor is made.”
3.How long do Java’s heap and stack memories last?
A developer needs to know a lot about core Java features, like memory. Your answer must show that you know how these two kinds of memory are different. You can describe each type of memory in a straightforward way.
Example: “Heap memory exists from the start of an application’s execution until the end. This kind of memory is also called “heap space,” and it’s where all the objects in Java are kept. Unlike heap memory, stack memory only exists while a thread is running, so its memory size is much smaller than the size of the heap space.
4. Name some of Java’s access modifiers
Give a short answer that tells us what the four modifiers are for this Java architecture question.
“In Java, the access modifiers are private, public, protected, and default.”
5. Give an example of an instance variable.
This is a question about how Java is built. You can answer by explaining what the term means, how things use it, and how it changes when things change.
“An instance variable is a variable that is set inside a class, linked to an object, and used outside of a method.” When the objects in that class use the instance variable, each object will make its own copy of the variable. So, if you make a change to an instance variable, it will only affect that instance and not the other instances of that variable.”
6. What is a major difference between an instance variable and a local variable?
This question about Java’s architecture needs a short answer that explains the difference between the two terms in terms of methods.
“Unlike an instance variable, which can be used in any method, a local variable can only be used within a specific method, block, or constructor.”
7.What does it mean for a Java method to be “final,” and what does it mean for a class to be “final?”
Give a short answer to this Java architecture question and show how the last term is used.
Example Answer: “Final is a word that means you can’t get to it. For instance, a “final method” is one that can’t be changed by the class that inherits it.
A class that is a subclass of a final class can’t extend it, but a final class can extend other classes.
8.What does Java’s JIT stand for, and what does it do?
Answer this question about architecture by explaining what the abbreviation means, when it is used, and what it does in terms of converting bytecode and compiling native code before execution.
“JIT” is an abbreviation for “just-in-time,” which is the name of a compiler that is turned on by default in Java. Every time a Java method is called, it starts to work.
The JIT compiler takes the method’s bytecode, which is written in Java, and turns it into instructions that are in the machine’s native code. The JIT compiler compiles this code just before it is sent to the processor so that it can be run.
9. Give two ways in which an object and a class are different.
You can answer this question about Java’s architecture by talking about how virtual reality and behavior are different.
Example answer: “One difference is that an object exists in virtual space, while a class is a construct that doesn’t exist in virtual space. The second difference is that an object has a certain way of acting, while a class is just a plan for how an object should act.
10.When comparing an interface class to an abstract class, which type supports multiple inheritance, allows only public members, and supports a single instance?
This question tests how well you know about classes. You can give a short answer that explains how these classes are different.
Example: “An interface class allows for more than one inheritance, but an abstract class only allows for one.” An interface class is the only one that can have a public member, while an abstract class can have a nonpublic member.
Java interview tips
Getting ready for your interview can be made easier by doing things like:
- Review what you know about Java. Make sure you know how to handle any situation that could come up with your Java skills. This will help you go into this kind of interview with confidence.
- Do more research on the most important Java interview questions. This can help you remember things about Java that you may have forgotten, and you should do it if you haven’t used Java in a while.
- Practice answering your questions. You can do this by acting out an interview with a friend who knows about Java. This will help you improve how you talk and give you more confidence.
