Java Interview Answers

A transient variable is a variable that may not be serialized.

An abstract class may contain code in method bodies, which is not allowed in an interface. With abstract classes, you have to inherit your class from it and Java does not allow multiple inheritance. On the other hand, you can implement multiple interfaces in your class.

String objects are immutable. StringBuffer supports mutable string.

According to the Java Language Specification, null, true, and false are technically literal values (sometimes referred to as manifest constants) and not keywords.

Multithreading is the ability to perform different tasks of a process simultaneously. This is achieved by using a separate thread for each task. Though there are several threads in a process, at a time the processor will handle only a single thread. Though it appears to be concurrent processing to the end user, internally only single thread will be running. Processor is able to multitask by switching between the threads.

When it comes to Multiprocessing there will be more than one processor and each thread will be handled by a different processor. Thus leading to concurrent processing of tasks.

The == operator checks to see if two objects are exactly the same object. Two strings may be different objects, but have the same value.The .equals() method to compare strings for equality(content).

JVM is a platform-independent programming language that converts Java bytecode into machine language and executes it.

Class variable is the variable used in the class, ie class members. Instance variables are the class objects

Synchronization is the way to make our program safe. It is used in multithreading. As we know when we have two or more threads that share a common code there can be some problem like inconsistent of data if one thread is updating data in that code. So if we make that sharable code (common code) synchronized then it ensures that at a given time only one thread will be having rights to access that code. Other threads can’t access the code until its free.

You can’t force GC, but could request it by calling System.gc(). JVM does not guarantee that GC will be started immediately.

Constructors must have the same name as the class and cannot return a value. They are only called once while regular methods could be called many times.

This is a way to organize files when a project consists of multiple modules. It also helps resolve naming conflicts when different packages have classes with the same names. Packages access level also allows you to protect data from being used by the non-authorized classes.

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