Java: ArrayList for storing doubles

Question

A very basic question but I am having a little bit of trouble, I am very new to Java (my only experience prior is VB.NET which I developed on for a couple of years but never really used any OOP principles)

I need an array implementation for a load of decimal numbers. I'm not sure how many I'll have so I need an array which can dynamically change it's size and I've been told an ArrayList is the way to go.

So I've tried this:

ArrayList<double> xCo = new ArrayList<double>();

And my compiler gets angry and asks me for a "reference" in space of where double goes. I'm certain I'm misunderstanding something the whole declaration process of these things so how am I supposed to go about doing it?

Thanks in advance :)

Answer 1

You can't use primitives in generics, use Double instead. Note the capitalization.

Answer 2

You cannot use java primitives in Generics , instead you have to use java primitive wrapper types

Change it to

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

Check this tutorial to learn more on Generics

• Generics Tutorial

Answer 3

使用Double而不是double，希望你导入了java.util.Arraylist包

Answer 4

你想要Double ，而不是double ：

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