What is an initialization block?

Question

We can put code in a constructor or a method or an initialization block. What is the use of initialization block? Is it necessary that every java program must have it?

Answer 1

Initializer block contains the code that is always executed whenever an instance is created. It is used to declare/initialise the common part of various constructors of a class.

The order of initialization constructors and initializer block doesn’t matter, initializer block is always executed before constructor.

What if we want to execute some code once for all objects of a class?

We use Static Block in Java.