In simple word, Constructor is a method like block of code which is called by Java runtime during object creation using new() operator. Constructor are special in sense that they have the same name as the Class they are part of. They are also special in a sense that they are called by JVM automatically when you create object. Have you ever thought about Why do you need constructor? What benefits it provide? One reason is to initialize your object with default or initial state, since default values for primitives may not be what you are looking for. One more reason you create constructor is to inform the world about dependencies, a class needs to do it's job. Anyone by looking at your constructors should be able to figure out, what he needs in order to use this class.  For example, following class OrderProcessor needs a Queue and Database to function properly.