Top 25+ Java Developer Interview Questions

Volatile keywords in Java can only be applied to individual variables but not to arrays or collections. The value of the Variable is always read from and written to the main memory when it is defined as volatile rather than being cached in a thread’s local memory. This makes it easier to make sure that all threads that access the variable can see changes made to it. The Dot operator in Java is used to access the instance variables and methods of class objects.

Object-oriented paradigm aims to incorporate the advantages of modularity and reusability. Objects are the instances of classes which interacts with one another to design applications and programs. There are the following features of the object-oriented paradigm. A Java developer should have a strong understanding of core Java concepts such as object-oriented programming, data types, control structures, and exception handling. Additionally, knowledge of frameworks like Spring, Hibernate, and web development technologies like Servlets and JSP is beneficial. Other than Technical Skills Problem-solving, debugging, and critical thinking skills are also highly valued.

“Can you explain the concept of the Java Virtual Machine (JVM) and its significance?”

An abstract class can have a combination of both abstract and non-abstract methods, whereas an interface has only abstract methods in it. Finally is used to execute the code written inside the block without handling any exceptions. Yes, the main method can be overloaded as many times as we want. Nevertheless, JVM prefers to call the main method with the help of its predefined calling method. System.out and System.err represent the monitor by default and thus can be used to send data or results to the monitor. System.in represents InputStream object which by default represents standard input device, i.e., keyboard.

The underlying data structure of the ArrayList is an array of the Object class. There are available readObject and writeObject methods specific to it. There are implemented and Serialization-capable versions of RandomAccess, Cloneable, and java.io (that are Marker Interface in Java). The method of Base class, i.e., baseMethod() is overridden in Derived class.

What is the difference between JDK, JRE, and JVM?

Iterable provides a way to iterate over a sequence of elements. Multitasking in Java refers to a program’s capacity to carry out several tasks at once. Threads, which are quick operations contained within a single program, can do this.

• In Java, you could indeed override a private or static method.
• We can also use ResultSet to update the data using updateXXX() methods.
• House can contain multiple rooms there is no independent life of room and any room can not belongs to two different houses if we delete the house room will automatically delete.
• In this code, we declare an array of size five and assign values to each element.

Method overriding is a method to achieve Run-time polymorphism in Java. Method overriding is a feature that allows a child class to provide a specific implementation of a method that is already provided by one of its parent classes. An interface in Java is a collection of static final variables and abstract methods that define the contract or agreement for a set of linked classes. Any class that implements an interface is required to implement a specific set of methods.

Why do we need wrapper classes?

This Java Developer interview profile brings together a snapshot of what to look for in candidates, with a balanced sample of suitable interview questions. ThreadStates is the enum with fixed constants fields START, RUNNING, WAITING, and DEAD. All enums implicitly extend the java.lang.Enum class and implement the Serializable and Comparable interfaces. The following example code shows how to use the extends keyword to create a subclass of the class Animal. The new class Cat inherits the variable from the Animal class and adds more code that only belongs to the Cat class. Some of the important methods of Java exception class are stated below.

Similarly, hibernate configurations are flexible and can be done from XML configuration file as well as programmatically. @Configuration, @ComponentScan and @Bean – for java based configurations. @PathVariable – for mapping dynamic values from the URI to handler method arguments. Exception Handling is a cross-cutting concern and Spring provides @ControllerAdvice annotation that we can use with any class to define our global exception handler. Spring MVC Framework provides the following ways to help us achieving robust exception handling. Autowiring enables the programmer to inject the bean automatically.

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It may or may not contain abstract methods but if a class has at least one abstract method, it must be declared abstract. In Java, it is not possible to modify the overridden method’s java 7 certifications scope. The subclass method’s scope must be equal to or wider than the Superclass method’s overridden method’s scope. It cannot, however, have a more exclusive scope like private.

• It can also be passed as an argument into the methods or constructors.
• To perform a backup of a MySQL database, you can use the mysqldump command-line tool, which creates a SQL dump file of the database.
• This process of dynamically growing an array is known as resizing.
• Synchronization is a process which keeps all concurrent threads in execution to be in sync.
• A static block in Java is a block of code that is executed when the class is loaded into memory.

It also allows the caller to remove elements from the underlying collection during the iteration. We can modify the throws clause of the Superclass method with some limitations, we can change the throws clause of the superclass method while overriding it in the subclass. The subclass overridden method can only specify unchecked exceptions if the superclass method does not declare any exceptions. If the superclass method declares an exception, the subclass method can declare the same exception, a subclass exception, or no exception at all.