arraylist找不到符号：方法addLast

Question

I'm having a problem with using the addLast method after declaring an ArrayList. Here's the class code:

import java.util.*;

public class Neuron{

        public int m_numInputs;
        public ArrayList<Double> m_vecWeight = new ArrayList<Double>();

        public Neuron(int numInputs){
                this.m_numInputs = numInputs + 1;

                //additional weight for bias
                for(int i = 0; i < numInputs + 1; ++i){
                        Random rand = new Random();
                        m_vecWeight.addLast(rand.nextFloat() * 2.0 - 1.0);

                }
        }

}

So the error I'm getting is:

cannot find symbol: method addLast(double), location: variable m_vecWeight of type ArrayList<Double>

Any guidance would be greatly appreciated.

Answer 1

The addLast() method exists in the LinkedList class, not in ArrayList . You can either:

1. Switch to use a LinkedList or
2. Simply call add() .

As stated in the documentation , addLast() is equivalent to add() .

Answer 2

Java ArrayList don't have addLast() method.

Use add() method from ArrayList to add in a specified index or use LinkedList which has addLast() method.

Appends the specified element to the end of this list.

This method is equivalent to add(E) .

Answer 3

You need to use add() method to add the element in the arraylist

change m_vecWeight.addLast(rand.nextFloat() * 2.0 - 1.0); to

 m_vecWeight.add(rand.nextFloat() * 2.0 - 1.0);