Cant delete node from doubly linked list

Question

This is the method which I am trying to do... Its always printing "Nothing to delete1" even if name to delete exist.

public String deleteName(String name){
    Node current, previous;
   
    String a ="";
     current = start;
     previous = null;
     
      while(current != null && !current.getData().getName().equals(name)  ){
         current = current.getNext();
         a = "Nothing to delete1"; 
      }
      if(current == null){
         a = "Nothing to delete";
      }
      
     if(current.getData().equals(name)){
        a = "name deleted";
        current.setPrevious(current.getNext());
        current.setNext(null);
        
     }

  return a;

}

Answer 1

Your problem is in how you update the links between different nodes to remove a particular node from the linked list.

current.setPrevious(current.getNext());

Above statement will set the previous link of the current node to the node next to the current node; this is not correct.

The above statement does the following operation:

|next node| <--- |current node|

To remove the current node, you need to:

1. Set the next of the previous node to point to the node next to the current node

   current.getPrevious().setNext(current.getNext());
   

   Basically, you want to do the following:

   |previous node| ---> |next node|
   

2. Set the previous of the node, next to the current node, to point to the node previous to the current node

   current.getNext().setPrevious(current.getPrevious());
   

   Here, you want to do the following:

   |previous node| <--- |next node|
   

After that, you can set the previous and next of the current node to null

current.setNext(null);
current.setPrevious(null); 

I would re-write your method as shown below:

public String deleteName(String name){
   
    String result = "";
    Node current = start;
    Node previous = null;
     
    while(current != null && !current.getData().getName().equals(name)){
       current = current.getNext();
    }
      
    if(current == null){
       result = "Nothing to delete";
    } else {
       current.getPrevious().setNext(current.getNext());
       current.getNext().setPrevious(current.getPrevious());

       current.setNext(null);
       current.setPrevious(null); 
       
       result = "name deleted";
    }

    return result;
}