CODEWITHSUNDEEP
javalist
Sandeep Sharma
Sandeep Sharma

Reputation: 1885

Java: add element after an element in the LinkedList

I want to add an element after an element in the list if list already contain that element otherwise I want to add this new element to beginning of the list.

Somehow below code is not working.

Any suggestions?

Does this approach correct performance wise?

public class HelloWorld
        {
          public static void main(String[] args) {
          LinkedList<Task> l =new LinkedList<Task>();

            l.add(new Task("a")); 
            l.add(new Task("b"));
            l.add(new Task("c")); 

            int index;

            if((index = l.lastIndexOf(new Task("a"))) != -1){
               l.add(++index, new Task("5"));
            }else{
               l.addFirst(new Task("6"));
            }        
            System.out.println(l);
      }
    }

    class Task{
     String value;

      Task(String v){
        value = v;
      }

      public boolean equals(Task t){
        return t.value.equals(this.value);
      }  

      public String toString(){  
       return this.value; 
      }
    }

Output produces: [6,a,b,c]

Expected output: [a,5,b,c]

Upvotes: 1

Views: 115

Answers (2)

byt3
byt3

Reputation: 115

Your equals should look like that.

@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;

    Task task = (Task) o;

    return value != null ? value.equals(task.value) : task.value == null;

}

Upvotes: 3

Mena
Mena

Reputation: 48404

You are not overriding Object#equals in your Task class.

You need to parametrize it with Object, otherwise it's an overload.

That in turn doesn't allow your new Task("a") to be equal to new Task("a"), as Object.equals in invoked instead, and the references don't match.

This in turn will cripple your lastIndexOf invocation with unexpected results.

Example

@Override
public boolean equals(Object obj) {
    // TODO your code, i.e. based on the "value" field
}

If you're using an IDE (which I recommend), you will have features allowing to draft equals (and hashCode) implementations based on your desired properties.

Upvotes: 5

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