Identifier Expected Error In Method Writing

public class Rational{
    public Rational (int numerator, denominator){
    if (denominator < 0){
        system.out.println("Denominator cannot be negative value. Changing rational to have positive denominator...");
        denominator = -denominator;
        numerator = -numerator;
    }
    if (denominator == 0){
        system.out.println("Denominator cannot be zero, reinput denominator.");
        int n = numerator;
        int d = denominator;
    }
}
//end of initialization
//behaviors
public Rational inverse(int n, d){
    if (numerator == 0){
        int temp = numerator;
        numerator = denominator;
        denominator = temp;
    }
    else system.out.println("Error, the inverse results in division by zero.");
}
public Rational simplify(int n, d){
    if (n%d == 0){
        return n;
    }
    else if (n < d){
        return simplify (d, n);
    }
    else return simplify(d, n%d);
    numerator = numerator / n;
    denominator = denominator /n;
}
}

New Java student here, and I’m running into an “indentifier expected” error on lines 2, 16, and 24. All those lines are public Rational, and the error points to the closing parentheses specifically. I’ve tried looking through similar questions on here, but I can’t figure out what’s wrong with mine. From what I saw the error has to do with defining methods outside of a block, but it looks like it’s in one to me. Any help would be appreciated!