Question

Let’s say I have an array:

int array[][] = {{1, 2, 3}, {2, 5, 7}, {4, 2, 1}};

How can I randomly make it

int array[][] = {{2, 5, 7}, {1, 2, 3}, {4, 2, 1}};

or

int array[][] = {{4, 2, 1}, {2, 5, 7}, {1, 2, 3},};

And so on.

Is there any JAVA function to help me? Or I have to figure it out by myself?

Thank you.

Answer 1

You might convert your array to a List<int[]> and call Collections.shuffle(). Then convert back to an array.

int array[][] = {{1, 2, 3}, {2, 5, 7}, {4, 2, 1}};

List<int[]> l = Arrays.asList( array ); //the list returned is backed by the array, and thus the array is shuffled in place
Collections.shuffle( l );
//no need to convert back

If you need to keep the original order, you’d have to create a copy of the array (or the list backed by that array), like this:

int array[][] = {{1, 2, 3}, {2, 5, 7}, {4, 2, 1}};

List<int[]> l = new ArrayList<int[]>( Arrays.asList( array ) );  //creates an independent copy of the list
Collections.shuffle( l );

int newArray[][] = l.toArray( new int[0][0] );

Another way:

int array[][] = {{1, 2, 3}, {2, 5, 7}, {4, 2, 1}};

int newArray[][] = array.clone(); //copy the array direcly
List<int[]> l = Arrays.asList( newArray );
Collections.shuffle( l );