How can I add a pair of numbers to an ArrayList?

I am trying to create an ArrayList with the dimensions of certain shapes. My code is:

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

shapes.add(2.5,3.5); 
shapes.add(5.6,6.5);
shapes.add(8.4,6.9);

I am aware this is doesn't work but how would I add a pair such as (2.5,3.5) to an array?

Make your own class:

public class MyClass {
   double x;
   double y;
   public MyClass(double x, double y) {
      this.x = x;
      this.y = y;
   }
}

Then make an ArrayList of that type:

ArrayList<MyClass> shapes = new ArrayList<>();

Adding to it:

MyClass pair = new MyClass(2.5,3.5);
shapes.add(pair);

If you want to get the x or the y coordinate, you can simply have additional methods in your class, for example public double getX() { return x; } and then you can do:

shapes.get(0).getX();

^{* This is only an example, modify the code as you see it fits your needs}