Implementation of ShellSort in Java.

ShellSort.java

package kr.opid.sorting;

public class ShellSort {
	public static void main(String[] args) {
		int[] array = new int[10];
		array[0] = 33;
		array[1] = 11;
		array[2] = 99;
		array[3] = 1;
		array[4] = 22;
		array[5] = 88;
		array[6] = 55;
		array[7] = 44;
		array[8] = 66;
		array[9] = 77;

		System.out.println("before)");
		displayArray(array);
		System.out.println();

		System.out.println("after)");
		shellSort(array);

	}

	static int[] shellSort(int[] arr) {
		int gap = 1;
		while (gap <= arr.length / 3) {
			gap = gap * 3 + 1; // 크누스 간격순서
		}
		while (gap > 0) {
			for (int i = gap; i < arr.length; i++) {
				int tmp = arr[i];
				int idx = i;

				while (idx > gap - 1 && arr[idx - gap] >= tmp) {
					arr[idx] = arr[idx - gap];
					idx -= gap;

				}
				arr[idx] = tmp;
			}
			gap = (gap - 1) / 3;
		}

		return arr;
	}

	/**
	 * 배열 출럭
	 * 
	 * @param arr
	 */
	static void displayArray(int[] arr) {
		for (int i = 0; i < arr.length; i++) {
			System.out.print(arr[i] + " ");
		}
	}
}

Why does it not show after??