Why we need constructer if we have methods in java . Ex-method like putData

Answer 1

Constructors allow us to directly initialize objects upon declaration, and is on most occasions more semantically fit to be used instead of calling setters after declaring the object.

https://stackoverflow.com/questions/19359548/setter-methods-or-constructors/42798426

Answer 2

Constructor itself is a method but without a return type.

Whenever you create an instance of a class then you do nothing but make a call to the constructor of the specific class to say that an object of the class has been created.

Object obj = new Object();

Even if you do not create a constructor, the compiler by default will create a no argument constructor for the class.