CODEWITHSUNDEEP
javaarrays
yak
yak

Reputation: 3930

Is there any way to make an ordinary array immutable in Java?

Googled for it, found plenty of code. But any of them gave me what I want. I want to make an ordinary array Immutable. I tried this:

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class test {

    public static void main(String[] args) {

        final Integer array[];

        List<Integer> temp = new ArrayList<Integer>();
        temp.add(Integer.valueOf(0));
        temp.add(Integer.valueOf(2));
        temp.add(Integer.valueOf(3));
        temp.add(Integer.valueOf(4));
        List<Integer> immutable = Collections.unmodifiableList(temp);

        array = immutable.toArray(new Integer[immutable.size()]);

        for(int i=0; i<array.length; i++)
            System.out.println(array[i]);

        array[0] = 5;

        for(int i=0; i<array.length; i++)
            System.out.println(array[i]);

    }
}

But it doesnt work, I CAN assign a 5 into array[0] ... Is there any way to make this array immutable?

Upvotes: 9

Views: 10064

Answers (3)

1218985
1218985

Reputation: 8022

You can also use Guava's ImmutableList, a high-performance, immutable, random-access List implementation that does not permit null elements. Unlike Collections.unmodifiableList(java.util.List), which is a view of a separate collection that can still change, an instance of ImmutableList contains its own private data and will never change.

Upvotes: 1

fge
fge

Reputation: 121740

If you want to use it as an array, you can't.

You have to create a wrapper for it, so that you throw an exception on, say, .set(), but no amount of wrapping around will allow you to throw an exception on:

array[0] = somethingElse;

Of course, immutability of elements is another matter entirely!

NOTE: the standard exception to throw for unsupported operations is aptly named UnsupportedOperationException; as it is unchecked you don't need to declare it in your method's throws clause.

Upvotes: 5

darijan
darijan

Reputation: 9785

It's impossible with primitive arrays.

You will have to use the Collections.unmodifiableList() as you already did in your code.

Upvotes: 3

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