ArrayList.get(index) not returning a variable?

Question

I am writing a neural net in Java, and I'm having trouble with an ArrayList.get() not returning a variable.

    double train(ArrayList<Double> inputVector, double desiredOutput) {
    double result = output(inputVector);
    double error = desiredOutput - result;
    double delta = learningRate_ * error * result * (1.0 - result);
    for (int i = 0; i < outputLayer_.weights_.size(); i++) {
        outputLayer_.weights_.get(i).doubleValue() += delta * lastOutput_.get(i);
    }
    ArrayList<Double> hiddenDelta = new ArrayList<Double>();
    for (int j = 0; j < hiddenLayer_.size(); j++) {
        double HiddenDelta = delta * outputLayer_.weights_.get(j + 1) * lastOutput_.get(j + 1) * (1 - lastOutput_.get(j + 1));
        for (int l = 0; l < hiddenLayer_.get(j).weights_.size(); l++) {
            hiddenLayer_.get(j).weights_.get(l) += HiddenDelta * inputVector.get(l);
        }
    }

The Error I get is on both of the lines that try to +=, each inside a for loop (1st and third) It tells me that a variable is expected. I am using JDK 8, with Intellij. I used the following to create the weights list:

ArrayList<Double> weights_ = new ArrayList<Double>();

Every List is initialized in a similar form.

This is not allowed. First get the value then add any value in it. — Braj
– Braj, Commented Jun 11, 2014 at 22:35
I tried using: hiddenLayer_.get(j).weights_.get(l).doubleValue() += HiddenDelta * inputVector.get(l); And it gave me the same error. — Cayleus
– Cayleus, Commented Jun 11, 2014 at 22:39

Roberto Linares · Accepted Answer · 2014-06-11 22:41:19Z

6

The expression outputLayer_.weights_.get(i).doubleValue() is readOnly. You cannot assign a value to it.

First place its value in a variable:

double newWeight = outputLayer_.weights_.get(i).doubleValue() + delta * lastOutput_.get(i);

Then assign the new calculated value:

outputLayer_.weights_.set(i, newWeight);

answered Jun 11, 2014 at 22:41

Roberto Linares

2,2253 gold badges23 silver badges35 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

ArrayList.get(index) not returning a variable?

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related