kth largest element in an array

public int (int[] nums, int k) {
    if (nums == null)
        return 0;
    Arrays.sort(nums);
    return nums[nums.length - k];
}

public int (int[] nums, int k) {
    if (nums == null)
        return 0;
    PriorityQueue<Integer> q = new PriorityQueue<>();
    for(int val : nums) {
        q.offer(val);

        if(q.size() > k) {
            q.poll();
        }
    }
    return q.peek();
}

public int (int[] nums, int k) {
    if (nums == null)
        return 0;
    int begin = 0, end = nums.length - 1;
    while (true) {
        int position = partition(nums, begin, end);
        if (position == k - 1)
            return nums[position];
        else if (position < k - 1) {
            begin = position + 1;
        } else
            end = position - 1;
    }
}

public int partition(int[] nums, int begin, int end) {
    int pivot = nums[begin];
    int left = begin + 1, right = end;
    while (left <= right) {
        while (left <= right && nums[left] >= pivot)
            ++left;
        while (left <= right && nums[right] <= pivot)
            --right;
        if (left <= right)
            swap(nums, left, right);
    }
    swap(nums, begin, right);
    return right;
}

public void swap(int[] nums, int i, int j) {
    int temp = nums[i];
    nums[i] = nums[j];
    nums[j] = temp;
}