How to add element to next free space in an array?

I'm trying to find a way to add an 开发者_如何转开发element to an array without knowing where to add it. E.g. Instead of doing something like this...

double[] myArray = new double[10];
myArray[5] = 1.0;

I want to be able to just add an element to the next available free space. Is this even possible in java? Sorry if it's a simple question, I'm pretty new to the language.

---

Firstly, define "free". You can't look for the first zero value; what if you actually wanted to store zero as a real value.

The only way is to keep track of where you last inserted:

double[] myArray = new double[10];
int nextIndex = 0;

myArray[nextIndex++] = 1234;
... etc

myArray[nextIndex++] = 1.0;

Note that this is deliberately simplistic. It does not protect against running off the end of the array etc.

Your better option is to use a Collection, like ArrayList, which expands automatically and is easy to add to.

---

Arrays don't have "free space". You can use a "magic value" (e.g. zero, or null depending on the type) to represent empty if you wish. Then you can search through the array looking for this value:

int i = Array.asList(array).indexOf(0.0);

A few warnings:

• This will be slow as it requires scanning the array.
• You must be certain that the magic value can't occur as an element that you wish to store in the array.

If you just want a collection that can contain a variable number of elements then don't use an array. For example, you could use an ArrayList and its add method to add elements to the end.

---

This makes far more sense for an array of object references, where null clearly means "empty". But let's just assume that for an array of double, maybe 0 means "empty". So...

int index = -1;
for (int i=0; i<array.length; ++i) {
    if (array[i] == 0) {
        array[i] = 5;
        index = i;
        break; 
    }
}

Then index points to the element you set, or is -1 if the array was full.