Fix that Java: Mugs are not the Same

public class Main {
    public static void main(String[] args) {
        Mug classic = new Mug(1.2);
        PlasticMug plastic = new PlasticMug(1.2, "polycarbonat");

        System.out.println(plastic.equals(classic));
    }
}

public class Mug {
    private double capacity;

    public Mug(double capacity) { this.capacity = capacity; }

    public double getCapacity() { return capacity; }

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (o == null) {
            return false;
        }
        if (!(o instanceof Mug)) {
            return false;
        }
       
        Mug other = (Mug) o;
        return other.capacity == this.capacity;
    }
}

public class PlasticMug extends Mug {
    private String plastic;
    public PlasticMug(double capacity, String plastic) {
        super(capacity);
        this.plastic = plastic;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (o == null) {
            return false;
        }
        if (!(o instanceof PlasticMug)) {
            return false;
        }
        
        PlasticMug other = (PlasticMug) o;
        return other.getCapacity() == this.getCapacity() && other.plastic.equals(plastic);
    }
}