Confusion in Constructor Overloading Example

Question

The following program gives output as

 I am Parameterized Ctor
 a = 0
 b = 0

---

public class ParameterizedCtor {

    private int a;
    private int b;

    public ParameterizedCtor() {
        System.out.println("I am default Ctor");
        a =1;
        b =1;
    }

    public ParameterizedCtor(int a, int b) {
        System.out.println(" I am Parameterized Ctor");
        a=a;
        b=b;

    }
    public void print() {
        System.out.println(" a = "+a);
        System.out.println(" b = "+b);
    }

    public static void main(String[] args) {

        ParameterizedCtor c = new ParameterizedCtor(3, 1);
        c.print();
    }

}

What is the reason?

Answer 1

this is called variable shadowing and default value of int is 0

make it like

 public ParameterizedCtor(int a, int b) {
        System.out.println(" I am Parameterized Ctor");
        this.a=a;
        this.b=b;
 }  

Also See

• Something about this

Answer 2

The un-initialized private variables a and b are set to zero by default. And the overloading c'tctor comes into place.ie, parameterCtor(int a, int b) will be called from main and the local variables a & b are set to 3 and 1, but the class variables a and b are still zero. Hence, a=0, b=0 (default c'tor will not be called).

To set the class variable, use:

this.a = a;
this.b = b;

Answer 3

You need to do this:

public ParameterizedCtor(int a, int b) {
    System.out.println(" I am Parameterized Ctor");
    this.a=a;
    this.b=b;
}

otherwise, you're just re-assigning the a and b parameters to themselves.