Question

The example is from a course, it’s for comparing two objects in java:

public class Complex {

    ...

    public boolean equals (Object obj) {
        if (obj instanceof Complex) {    // if obj is "Complex" (complex number) 
            Complex c =  (Complex) obj   // No idea
            return (real == c.real) && (imag == c.imag); 
            // I'm guessing real means [this].real
        }
        return false;
    }
}

So, my question is: “what does this: Complex c = (Complex) obj actually mean” ?

Also I’ve worked with python and c++, java is new for me.

Answer 1

See my comments inline.

    public class Complex {

...

public boolean equals (Object obj) {
    if (obj instanceof Complex) {    // you first need to check whetever the obhect passed to the equal method is indeed of type "Complex" because i guess what you want here is to compare two Complex objects.
        Complex c =  (Complex) obj   // If the object is complex then you need to treat it as complex so cast it to Complex type in order to compare the "real" and "imag" values of the object.
        return (real == c.real) && (imag == c.imag); 
        // I'm guessing real means [this].real
        // yes, it does.
    }
    return false;
}

}

Read more about type casting at here

You can also check boxing and unboxing concept.

Hope this helps,
Dan