Flip an array on its head?

Ok, did my researching and haven't found anything.

In Java, a 2D array usually prints down and then left (or left then down depending on how you word your for loops). But how can I take that same array, and print it left and up? I don't want t开发者_开发百科o flip the array itself because I plan to add on to it (So say, instead of having 18 rows, have idk, 30 mid-game).

So my question is: how can you print a 2D array in Java from bottom, up?

Start from the end:

for (int i = arr.length - 1; i >=0; --i) {
    for (int j = arr[i].length -1; j >= 0; --j) {
         System.out.println(arr[i][j]);
    }
}

Although the other answers are easier and more terse, if you do this often, you could alternately write an Iterator that would traverse the array in reverse order:

public class ReverseArrayIterator<T> implements Iterator<T> {
    private final T[] myArray;
    private int pointer;

    public ReverseArrayIterator(T... myArray) {
        this.myArray = myArray;
        pointer = myArray.length;
    }

    @Override
    public boolean hasNext() {
        return pointer > 0;
    }

    @Override
    public T next() {
        if (!hasNext())
            throw new NoSuchElementException();
        return myArray[--pointer];
    }

    @Override
    public void remove() {
        throw new UnsupportedOperationException();
    }
}

If you mean that "down and left" is this:

for (int i = 0; i < arr.length; i++) {
    for (int j = 0; j < arr[i].length; j++) {
        System.out.print(arr[i][j] + " ");
    }
    System.out.println();
}

then "bottom up" would be something like this:

for (int i = arr.length-1; i >= 0; i--) {
    for (int j = arr[i].length-1; j >= 0; j--) {
        System.out.print(arr[i][j] + " ");
    }
    System.out.println();
}

... Reverse the indices in the for loop ...

Or, if you're using the new fast enum for loop, switch to indices.

Or, index by array.length - i - 1