Misunderstanding how to use no args constructor

My instructions were to make a no-argument constructor with default values.

I am having difficulty setting up proper constructors to initialize my class variables re and im. I tried to create a default constructor and use it, but I have a number of errors indicating that I am not doing it correctly.

public class Complex {
    // Constants (final)
    protected double re;   // the real part
    protected double imag;   // the imaginaryinary part
    // Variables
    public double product;

   public Complex() {}  

    // create a new object with the given real and imaginaryinary parts
    Complex() {
        this.re = real;
        imag = imaginary;
    }
....... Code goes on

I think, most of my problems is that I have to do with my constructor and lack of this.

 // create a new object with the given real and imaginaryinary parts
Complex() {
    this.re = 1.0;
    this.imag = 2.0;
}