Variable expected error

Question

I am trying to make a bot that selects a random joke from an array list, but I seem to get an error that says:

Variable expected

My code so far is:

package com.delta.objects;

import java.util.ArrayList;

/**
 * Created by WILLIAM on 8/3/2015.
 */
public class JokeBot extends Bot {

    public ArrayList<Joke> jokesIKnow = null;

    public JokeBot(ArrayList<Joke> jokesIKnow) {
        this.jokesIKnow = jokesIKnow;
    }

    public void tellJoke(){

        Double randomNumDouble = new Double(Math.random() = jokesIKnow.size());
        int randomNum = randomNumDouble.intValue();


    }

    protected void sayJoke(Joke aJoke){
        talk(aJoke.getJokeSetup());
        talk(aJoke.getJokePunchline());
    }
}

the error comes up for:

Double randomNumDouble = new Double(Math.random() = jokesIKnow.size());

Answer 1

Double randomNumDouble = new Double(Math.random() = jokesIKnow.size());

That's some very invalid syntax. You can't assign the return value of a method (in this case jokesIKnow.size() is a method which returns something) to anything except a variable. For example, this is legal:

int numberOfJokes = jokesIKnow.size();

Here you are trying to assign it to another method. Perhaps you mean to write Math.random(jokesIKnow.size()) which passes the variable into the random generator.