OOP, Two constructors are called. One constructor without the proper parameter.

[Jae An]

I'm having trouble understanding the sample code from my textbook. The main method calls both constructors. I'm confused why this happens although the constructor in class B does not have an int as a parameter. Thank you for your time.

package Chapter11;

public class Test extends Object {
    public static void main(String[] args) {
        A a = new A(3);
    }
}

class A extends B {
    public A(int t) {
        System.out.println("A constructor");
    }
}

class B {
    public B() {
        System.out.println("B constructor");
    }
}

[Tushar Goel]

HI Jae, do you aware of 'super()' ?

In a sub class constructor, compiler runs 'super()' as the first statement. This is implicit call and happens automatically by the compiler. In your case,
class B is super class and class A is sub class. So when you call class A constructor it will call 'super()' implicitly which then calls super class no args constructor.
that's why you see first B class constructor statement executes then A class statement executes.

[Campbell Ritchie]

… and welcome to the Ranch

[Campbell Ritchie]

The full details of the object creation process are in the Java® Language Specification (=JLS), I think this section. Beware: the JLS can be difficult to read.

[Campbell Ritchie]

And when you read the JLS link you will find that three constructors are called when you run your program.