Why does value of the variable changes for all objects [closed]

Answer 1

Static member belong to whole class, So if you change it all instance get affected.

Use

private int age; // without static.

Answer 2

Use:

private int age;

static variables are shared between all instances.

Answer 3

static variables are class variables so, remove static from variable declaration as :

private int age;

as per java docs :

Fields that have the static modifier in their declaration are called static fields or class variables. They are associated with the class, rather than with any object. Every instance of the class shares a class variable, which is in one fixed location in memory.