我怎样才能 append 到这个 java 链表？

Question

I need to create a linkedlist. I need to add a method to a class UnsortedBulbList to append to the linkedlist. However, I keep getting the error:Cannot find Symbol. I've been stuck on this for way too long... any help would be greatly appreciated!

'''

import java.util.Objects;

public class Bulb{
    private String manufacturer;
    private String partNumber;
    private int wattage;
    private int lumens;
    public Bulb(String m, String p, int w, int l){
        manufacturer = m;
        partNumber = p;
        wattage = w;
        lumens = l;

        }
    public String getManufacturer(){
        return manufacturer;
    }
    public String partNumber(){
        return partNumber;
    }
    public int wattage(){
        return wattage;
    }
    public int lumens(){
        return lumens;
    }
    public void setManufacturer(String m){
        if (m==null){
            throw new IllegalArgumentException("Bad manufacturer");
        }
        manufacturer = m;
    }
    public void partNumber(String p){
        if (p==null){
            throw new IllegalArgumentException("Bad partNumber");
        }
        partNumber = p;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Bulb)) return false;
        Bulb bulb = (Bulb) o;
        return wattage == bulb.wattage &&
                lumens == bulb.lumens &&
                manufacturer.equals(bulb.manufacturer) &&
                partNumber.equals(bulb.partNumber);
    }

    @Override
    public int hashCode() {
        return Objects.hash(manufacturer, partNumber, wattage, lumens);
    }

    public void wattage(int w){
        if (w<0){
            throw new IllegalArgumentException("Bad wattage");
        }
        wattage = w;
    }

    @Override
    public String toString() {
        return "Bulb{" +
                "manufacturer='" + manufacturer + '\'' +
                ", partNumber='" + partNumber + '\'' +
                ", wattage=" + wattage +
                ", lumens=" + lumens +
                '}';
    }

    public void lumens(int l){
        if (l<0){
            throw new IllegalArgumentException("Bad manufacturer");
        }
        lumens = l;

    }


}

public class BulbList {
    BulbNode first;
    BulbNode last;
    private int length;

    public BulbList () {
        BulbNode ln = new BulbNode();
        first = ln;
        last = ln;
        length = 0;
    }

    public void append (Bulb s) {
        BulbNode n = new BulbNode(s);
        last.next = n;
        last = n;
        length++;
    }

//    public LinkedListIterator reset()   {
//        return new LinkedListIterator(first.next);
//    }

}

public class UnsortedBulbList extends BulbList{
    public UnsortedBulbList(){
    }
    void add(Bulb u){

        u.append();
    }
}

'''

When I run it, I get the error: Cannot find symbol symbol:method append Location: variable u of type bulb

Answer 1

The mistake here is that you are trying to use the append method of the Bulb class, which doesn't exist. Instead, I think you wanted to call the append method of the parent class, like:

public class UnsortedBulbList extends BulbList{
    public UnsortedBulbList(){
    }
    void add(Bulb u){

        super.append(u);
    }
}