How to initialize a static SparseArray

Question

How can I initialize a static, unmodifiable instance of android.util.SparseArray?

You don't initialize static properties. What exactly are you trying to do? — Cat, May 05 '13 at 23:01
@Eric the SparseArray equivalent of this answer http://stackoverflow.com/a/507658/884677 for a static map — firyice, May 05 '13 at 23:08
@Eric yes, exactly as I stated in this question, and the linked question/answer — firyice, May 06 '13 at 00:30
You're better off using a HashMap for this purpose. I tried tackling the same problem. — IgorGanapolsky, Dec 11 '15 at 16:00

score 16 · Answer 1 · edited Dec 26 '17 at 09:16

16

Here is a better way using an anonymous class:

static final SparseIntArray myArray = new SparseIntArray() {
    {
        append(1, 2);
        append(10, 20);
    }
};

edited Dec 26 '17 at 09:16

frogatto

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answered Dec 19 '13 at 02:43

Peter

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score 10 · Accepted Answer · edited May 23 '17 at 11:47

You cannot do what you are attempting to. At least, not how you are attempting to do it. There is no implementation of SparseArray that is unmodifiable.

However, you could create one. Here's how:

Create a class, say CustomSparseArray<E>, and have it extend SparseArray.

Override all methods that change the elements in the array, and replace them with something like this:

@Override
public void append(int key, E value) {
    if (mLocked)
        return; // Maybe throw an exception
    super.append(key, value);
}

Then, add in a member variable to the class, boolean mLocked = false;.
Next, you need a method like the following:
```
public void lock() { mLocked = true; }
```

Lastly, implement your static variable using a method similar to in the other post:

public class Test {
    private static final CustomSparseArray<Integer> myArray;
    static {
        myArray = new CustomSparseArray<Integer>();
        myArray.append(1, 1);
        myArray.append(2, 5);
        myArray.lock();
    }
}

Then you have an unmodifiable SparseArray in your static variable myArray.

score 1 · Answer 3 · answered Mar 06 '17 at 09:23

1

This works for me:

static final SparseIntArray CMyArray = new SparseIntArray();
static {
    CMyArray.append(2, 4);
    CMyArray.append(8, 3);
    CMyArray.append(255, 1);
}

as per: https://docs.oracle.com/javase/tutorial/java/javaOO/initial.html

answered Mar 06 '17 at 09:23

PJ_Finnegan

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How to initialize a static SparseArray

3 Answers3