Core Java interview questions and Answers

The static import feature allows the static member of a class to be accessed directly without using the qualified name. The biggest advantage of this feature is that less coding will be required if you have access to a static member.

It is a reference type that is similar to a class in Java. It is a collection of abstract methods that is used for full abstraction. An interface may have methods and variables but the methods in interface are abstract by default.

It is an interfaces that has no field or methods (empty interface). It helps in conveying to the JVM that the class that is implementing the interface of a category will have special behavior. It is also known as tag interface.

There are 4 major marker interfaces:

• Searilizable interface
• Cloneable interface
• Remote interface
• ThreadSafe interface

Annotation is a tag in Java that represents metadata attached with a class, method, interface, or field. It provides supplement information to be used by compiler and JVM. Annotations do not change a compiled program's action and they are not pure comments.

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It is a class that is a member of another class.

There are 4 types of inner classes:

• Nested Inner class
• Method Local inner classes
• Anonymous inner classes
• Static nested classes

Class loaders help in loading classes during runtime to the Java Virtual Machine. In addition, they are part of the Java Runtime Environment. Hence, due to class loaders, JVM is not required to know the underlying files for running programs.

There are 3 types of built-in Class Loaders:

• Bootstrap Class Loader: Loads internal classes
• Extensions Class Loader: Loads classes from extensions directory
• System Class Loader: Loads classes from the current classpath

Java will automatically create default constructors if there are no default constructors written by you.

The default constructor will call parent default constructor and initialize member data variable to default values.

It is the process through which Java programs perform memory management. When the Java programs run on JVM, objects get created in a part of the memory that is dedicated to program. When objects are no longer needed, the garbage collector finds and deletes them to free up program memory.