Strings - General Questions

What is the output of the following program?

public class Main {
    public static void main(String[] args) {
        String s = "Java";
        s.concat(" rocks");
        System.out.println(s);
    }
}

What is the output of the following program?

public class Main {
    public static void main(String[] args) {
        System.out.println("a,b,,c".split(",").length);
    }
}

What is the output of the following program?

public class Main {
    public static void main(String[] args) {
        System.out.println("abc".compareTo("abd"));
    }
}

What is the output of the following program?

public class Main {
    public static void main(String[] args) {
        String s = "Programming";
        System.out.println(s.substring(3, 7) + " " + s.indexOf('g') + " " + s.charAt(0));
    }
}

What is the output of the following program?

public class Main {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder("abc");
        sb.append("d").reverse();
        System.out.println(sb);
    }
}