What is the purpose of constructors in Java if variables already have default values?

2 weeks ago 24
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I am learning core Java and had a conceptual doubt about constructors.

In Java, instance variables are automatically assigned default values (for example, 0 for int, null for objects, and false for boolean). Because of this, I am confused about the actual necessity of constructors.

I understand that constructors are used to initialize objects, but if default initialization already happens, what additional purpose do constructors serve?

example-

class Student { int id; String name; } public class Test { public static void main(String[] args) { Student s = new Student(); System.out.println(s.id); // 0 System.out.println(s.name); // null } }

Since the object already contains valid default values without defining any constructor, in what real-world scenarios is defining a constructor necessary or recommended?

I am looking for a conceptual explanation with practical use cases, rather than a language reference definition.

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