invalid method declaration; return type required for a linked list

Question

I'm having trouble developing a linked list class to mimic standard string and string builder classes in Java.

I'm trying to learn how to use and manipulate Linked Lists, and I want to make a class called LString that is a string object made from a linked list of characters, instead of arrays.

So far, this is how I understand to set up a Linked List class:

public class LString    {

    //Fields
    node front;
    //node tail;?
    int size;

    // Node class
    private class node {

        char data;
        node next;

        //constructors
        //default
        public node (){
        }

        //data
        public node (char newData){
             this.data = newData;
        }

        //data + next
        public node (char newData, node newNext){
             this.data = newData;
             this.next = newNext;
        }



    // Constructors
    public LString(){
        this.size = 0;
        this.front = null;
    }

    //Methods

    //append
    public void append (char data){

        this.size++;

        if  (front == null){
             front = new node(data);
             return;
        }

        node curr = front;
        while (curr.next != null){
             curr = curr.next;
        }

        curr.next = new node(data);

    }

    //prepend
    public void prepend (int data){     
        front = new node(data, front);
        size++;
    }

    //delete
    public void delete(int index){
    //assume that index is valid
        if (index == 0){
             front = front.next;
        } else {
             node curr = front;
             for (int i = 0; i < index - 1; i++){
                curr = curr.next;
             }
             curr.next = curr.next.next;
        }
        size--;

    }

    //toString
    public String toString(){
        StringBuilder result = new StringBuilder();
        result.append('[');

        node curr = front;
        while (curr != null){
            result.append(curr.data);
            if  (curr.next != null){
                result.append(',');
            }
            curr = curr.next;
        }

        result.append(']');
        return result.toString();
    }

    //add (at an index)
    public void add(int index, int data){
         if (index == 0){
              front = new node(data, front);
         }  else {
              node curr = front;
              for (int i =  0;  i < index - 1;  i++){
                    curr = curr.next;
              }
              curr.next = new node(data, curr.next);
         }
     }
}

I am receiving this error message:

LString.java:41: error: invalid method declaration; return type required
public LString(){

I have seen other solutions to this problem by adding something like this:

public static void main(String[] args) {
  LString lstring = new LString();
}

but that didn't work for me. Any help is appreciated.

Answer 1

You need to close the bracket of node inner class. In the given code, public LString() function is defined inside node class so it should have return type.