Pancake sort inteview using java
Flip


Use better variable names. i and j are harder to read than something like front and back.
It's preferable to define the temp value inside the loop and save a line of code.
The method should be private.
Depending on what the interviewer wants, it's much nicer to make a new array than to destructively modify the existing one. I'll assume you asked and they specified to modify the existing array. That being the case, you don't need to return the modified array.


Pancake Sort


You're not doing a pancake sort. It's nonsensical for you to describe a problem and then ask us to review code that breaks your own stated invariants to solve the problem. 
-1000 is arbitrary. Use Integer.MIN_VALUE and your code will work for all negative numbers.
Don't use abbreviations or shorten variable names. The extra letters don't cost anything. max and maxPos are not sufficiently descriptive. Don't use c as an array index. Either use j or a descriptive name.
In the comments, you observe that pancake sort is inefficient. Yes, it is. The point was to pick a sort that most people haven't thought about so everybody starts on an even playing field for the interview question. The inefficiency is tied to the algorithmic limitation of only having flip() available. There are no significant performance gains to be had unless you break that limitation, at which point you're no longer doing a pancake sort.


Using an actual pancake sort and my other suggestions, your code might look something like:

class Solution {

    // return an int for convenient testing
    private static int[] pancakeSort(final int[] array) {
        boolean sorted = false;
        while (!sorted) {
            sorted = true;
            for (int i = 0; i &lt; (array.length - 1); i++) {
                if (array[i] &gt; array[i + 1]) {
                    flip(array, i + 1);
                    flip(array, i + 2);
                    flip(array, i + 1);
                    sorted = false;
                    break;
                }
            }
        }
        return array;
    }

    private static void flip(final int[] array, final int elementsToFlip) {
        for (int front = 0, back = elementsToFlip - 1; front &lt; back; front++, back--) {
            final int temp = array[front];
            array[front] = array[back];
            array[back] = temp;
        }
    }

    public static void main(final String[] args) {
        System.out.println(Arrays.toString(pancakeSort(new int[] { 1 })));
        System.out.println(Arrays.toString(pancakeSort(new int[] { 1, 2 })));
        System.out.println(Arrays.toString(pancakeSort(new int[] { 2, 1 })));
        System.out.println(Arrays.toString(pancakeSort(new int[] { 1, 2, 3 })));
        System.out.println(Arrays.toString(pancakeSort(new int[] { 2, 1, 3 })));
        System.out.println(Arrays.toString(pancakeSort(new int[] { 3, 1, 2 })));
        System.out.println(Arrays.toString(pancakeSort(new int[] { 3, 2, 1 })));
        System.out.println(Arrays.toString(pancakeSort(new int[] { 3, 2, 1, 8, 4, 6, 5, 10, 7, 9 })));
    }
}