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Java has been a perennial contributor to the software development domain. It is not only necessary to learn and master Java skills but also to practice these skills in real-time. In this article, we bring you, some of the most sought after Java Interview Questions that will help you ace major interview processes and help test your skills and knowledge at its absolute. You can access various programming and technical courses on Great Learning Academy and get your free certificates.
It's a no-brainer that Java is one of the leading programming options for bagging a lucrative job. After all, the class-based, general-purpose, object-oriented programming language is one of the most widely used programming languages in the world. So, here are top interview questions on Java and answers that will help you bag a Java job or, at the very least, enhance your learning. The Java interview questions are recommended for both beginners and professionals as well as for Software Developers and Android Applications Developers.
We also recommend you to brush up on your Java skills with this Java Cheat Sheet before starting your Java interview preparation. This article is only relevant for Core Java Interview.
The article has been divided into different sections and categories for your organized preparation for the interview into the following categories:.
Answer: Java is an object-oriented, high-level, general-purpose programming language originally designed by James Gosling and further developed by the Oracle Corporation. It is one of the most popular programming languages in the world. To know more about what is Java, Click here and know all the details of Java, Features, and Component. Answer: JVM is a program that interprets the intermediate Java byte code and generates the desired output.
It is because of byte code and JVM that programs written in Java are highly portable. You may want to check out Java features in detail here. Answer: In the Just-in-Time compilation, the required code is executed at run time. Typically, it involves translating bytecode into machine code and then executing it directly.
For enabling high performance, Java can make use of the Just-In-Time compilation. The JIT compiler is enabled by default in Java and gets activated as soon as a method is called.
It then compiles the bytecode of the Java method into native machine code. After that, the JVM calls the compiled code directly instead of interpreting it. This grants a performance boost. Answer: JIT compiler runs after the program is executed and compiles the code into a faster form, hosting CPU's native instructing set. JIT can access dynamic runtime information, whereas a standard compiler doesn't and can make better optimizations like inlining functions that are used frequently.
Answer: Java programming language does not depend on any particular hardware or software because it is compiled by the compiler and then converted into byte code.
Byte code is platform-independent and can run on multiple systems. The only requirement is Java needs a runtime environment, i.
Answer: The concept of assigning a variable of one data type to a variable of another data type. It is not possible for the boolean data type. After execution, i will contain only 3 and would truncate the rest when we go from float to integer. Answer: Access modifiers are predefined keywords in Java that are used to restrict the access of a class, method, constructor, and data member in another class. Answer: The local variables are not initialized to any default value, neither primitives nor object references.
Answer: OOPs is a programming paradigm centred around objects rather than functions. It is not a tool or a programming language it is a paradigm that was designed to overcome the flaws of procedural programming.
Some frameworks also follow OOPs concepts, Angular is one such framework. Answer: An instance of a Java class is known as an object. Two important properties of a Java object are behaviour and state. An object is created as soon as the JVM comes across the new keyword. Answer: A class is a collection of objects of similar data types. Classes are user-defined data types and behave like built-in types of a programming language.
Answer: A class has two sections one declares variables, and other declares method, and these are called instance variables and instance methods, respectively. They are termed so because every time a class is instantiated, a new copy of each of them is created.
Variables and methods can be created that are common to all objects and accessed without using a particular object by declaring them static. Static members are also available to be used by other classes and methods. Answer : A constructor is a method that has the same name as that of the class to which it belongs.
As soon as a new object is created, a constructor corresponding to the class gets invoked. Although the user can explicitly create a constructor, it is created on its own as soon as a class is created. This is known as the default constructor. Constructors can be overloaded.
Note : - If an explicitly-created constructor has a parameter, then it is necessary to create another constructor without a parameter. Answer : Variables that are only accessible to the method or code block in which they are declared are known as local variables. Instance variables, on the other hand, are accessible to all methods in a class.
While local variables are declared inside a method or a code block, instance variables are declared inside a class but outside a method. Even when not assigned, instance variables have a value that can be null, 0, 0. This isn't the case with local variables that need to be assigned a value, where failing to assign a value will yield an error.
Local variables are automatically created when a method is called and destroyed as soon as the method exits. For creating instance variables, the new keyword must be used.
Answer : Method Overriding in Java allows a subclass to offer a specific implementation of a method that has already been provided by its parent or superclass.
Method overriding happens if the subclass method and the Superclass method have:. Answer: Overloading is the phenomenon when two or more different methods method overloading or operators operator overloading have the same representation. Similarly, an overloaded function called Add can be used for two purposes. Unlike method overriding, method overloading requires two overloaded methods to have the same name but different arguments.
The overloaded functions may or may not have different return types. Answer : The final keyword in Java is a non-access modifier that applies only to a class, method, or variable.
It serves a different purpose based on the context where it is used. When a class is declared as final, then it is disabled from being subclassed i. A variable followed by the final keyword is not able to change the value that it holds during the program execution. So, it behaves like a constant. Answer : An array necessitates for giving the size during the time of declaration, while an array list doesn't necessarily require size as it changes size dynamically.
To put an object into an array, there is the need to specify the index. However, no such requirement is in place for an array list. While an array list is parameterized, an array is not parameterized. Answer: String variables are stored in a constant string pool. With the change in the string reference, it becomes impossible to delete the old value. For example, if a string has stored a value "Old," then adding the new value "New" will not delete the old value.
It will still be there, however, in a dormant state. In a String Buffer, values are stored in a stack. With the change in the string reference, the new value replaces the older value. The String Buffer is synchronized and therefore, thread-safe and offers slower performance than the String Builder, which is also a String Buffer but is not synchronized. Hence, performance is fast in String Builder than the String Buffer. Answer: The collection of strings stored in the heap memory refers to the String pool.
Whenever a new object is created, it is checked if it is already present in the String pool or not. If it is already present, then the same reference is returned to the variable else new object is created in the String pool, and the respective reference is returned.
Answer : A Java interface is a template that has only method declarations and not method implementations. It is a workaround for achieving multiple inheritances in Java.
Some worth remembering important points regarding Java interfaces are:. Answer : There are several differences between an Abstract class and an Interface in Java, summed up as follows:. Answer : An abstract class in Java is a class that can't be instantiated. Such a class is typically used for providing a base for subclasses to extend as well as implementing the abstract methods and overriding or using the implemented methods defined in the abstract class.
To create an abstract class, it needs to be followed by the abstract keyword. Any abstract class can have both abstract as well as non-abstract methods. A method in Java that only has the declaration and not implementation is known as an abstract method. Also, an abstract method name is followed by the abstract keyword. Any concrete subclass that extends the abstract class must provide an implementation for abstract methods.
Answer: If a subclass or child class has two parent classes, that means it inherits the properties from two base classes, it is multiple inheritances. Java does not multiple inheritances as in case if the parent classes have the same method names, then at runtime, it becomes ambiguous, and the compiler is unable to decide which method to execute from the child class.
The functionality of the objects decides how they are grouped. Packagers act as "containers" to classes. A disadvantage of using the thread class is that it becomes impossible to extend any other classes.
Answer : The yield method belongs to the thread class. It transfers the currently running thread to a runnable state and also allows the other threads to execute.
In this article, we have compiled the most frequently asked Java Interview Questions. These questions will give you an acquaintance with the type of questions that an interviewer might ask you during you interview for Java Programming. As a Fresher, you have either just attended an interview or planning to attend one soon. An Entry Level jobseeker looking to grow your career in software programming , you may be nervous about your upcoming interviews. All of us have those moments of panic where we blank out and might even forget what a thread is. We will simplify it for you, all you need to do it take a deep breath and check the questions that are most likely to be asked.
There is the list of core Java interview questions. If there is any core Java interview question that has been asked to you, kindly post it in the ask question section. The answers to the Core Java interview questions are short and to the point. The core Java interview questions are categorized in Basics of Java interview questions, OOPs interview questions, String Handling interview questions, Multithreading interview questions, collection interview questions, JDBC interview questions, etc. Java is the high-level, object-oriented , robust, secure programming language, platform-independent, high performance, Multithreaded, and portable programming language. It was developed by James Gosling in June
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