Two different variables pointing to the same memory location

Question

I would like to use different variables to access the same data.

i.e. I have an array:

float[] vector = new float[3];

I would like each value in the array to also have its individual label i.e.:

vector[0] == pitch;
vector[1] == yaw;
vector[2] == roll;

I would like to use vector[] & pitch/yaw/roll interchangeably. When I pass all three values between two functions I want to refer to the array, however when I access them individually I would like to refer to them as pitch yaw and roll.

Is this possible in Java?

@ Lee Meador Yes, I tried what Jace J McPherson suggested, but as pointed out, that does not work. @ Juvanis - I am of course aware of that option. However I was wondering if there where a 'less brute force' method of doing it, partly because it would be useful, partly 'academic interest' — user2620379, Jul 25 '13 at 21:36

Louis Wasserman · Answer 1 · 2013-07-25T21:28:11.743

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This isn't possible the way you mean. You can't set pitch = 20 and get vector[0] == 20; primitives, at least, don't work that way in Java. What you could do, though -- what you should do -- is create a class named Vector with methods named setPitch, getPitch, etc, and use the float[3] as an internal implementation detail.

edited Jul 25 '13 at 21:28

answered Jul 25 '13 at 20:37

Louis Wasserman

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yep. that makes sense. basically the same thing Andy Thomas is saying. – user2620379 Jul 26 '13 at 13:41

score 2 · Accepted Answer · answered Jul 25 '13 at 21:09

You can't do this with a primitive float and an array of type float[]. Java does not support variables that are pointers or references to primitives.

However, there are a few workarounds.

First, you could make your own mutable reference type holding a float value.

MyFloat[] vector = new MyFloat[3] { new MyFloat(p), new MyFloat(y), new MyFloat(r) };
MyFloat pitch = vector[0];
MyFloat yaw = vector[1];
MyFloat roll = vector[2];

But it would probably be better to wrap your array in an object, and use methods to get the members by meaningful name, rather than variables.

public class Orientation {
  private float[] vector = new float[3];

  public float[] getArray() { return vector; }

  public pitch() { return vector[0]; }
  public yaw() { return vector[1]; }
  public roll() { return vector[2]; }

  public setPitch( float pitch ) { vector[0] = pitch; }
  public setYaw( float yaw ) { vector[1] = yaw; }
  public setRoll( float roll ) { vector[3] = roll; }
}

This gets you close -- although you can't just say pitch, you could say o.pitch().

Just noticed that Louis Wasserman had already suggested encapsulation. He should get the credit for that. I'm leaving this answer since it's filled out a bit more. — Andy Thomas, Jul 25 '13 at 21:17

score 0 · Answer 3 · answered Jul 25 '13 at 20:38

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Passing a primitive data type in java only send a copy of its data to the requested method. If you are looking to pass a Reference to the value (rather than a copy), then you should use the Object form of the variables.

So, use Float in place of float. This will make your numbers Object variables rather than primitive data types.

answered Jul 25 '13 at 20:38

Jace J McPherson

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-1: Even if you use `Float`, this won't be possible for two reasons: 1. `Float` object references (as other primitive wrapper classes) are **immutable**. 2. Java is **pass by value**, no matter what. Refer to [Is Java “pass-by-reference”?](http://stackoverflow.com/q/40480/1065197). – Luiggi Mendoza Jul 25 '13 at 20:41

Two different variables pointing to the same memory location

3 Answers3