JAVA吸血鬼数字

     初读java编程思想,看到了吸血鬼数字的问题

public class DemoApplication1 {
    public static void main(String[] args) {
        demo();
    }
    /**
     * 4位数吸血鬼数字
     */
    public static void demo() {
        int result = 0;
        StringBuilder content = new StringBuilder("");
        int[] a = new int[10000];
        for (int i = 1; i < 100; i++) {
            for (int j = 1; j < 100; j++) {
                result = i * j;
                if (result > 1000 && result < 10000 && result % 100 != 0) {
                    if (testEquals(i, j, result, content)) {
                        System.out.println(i + "*" + j + "=" + result);
                    }
                }

            }
        }
    }


    private static boolean testEquals(int a, int b, int c, StringBuilder content) {
        int[] aAndB = toIntArray(a, b);
        int[] cArr = toIntArray(c);
        sort(aAndB);
        sort(cArr);
        String resultString = Arrays.toString(aAndB) + Arrays.toString(cArr) + c;
        if (testEquals(aAndB, cArr) && !content.toString().contains(resultString)) {
            content.append(",").append(resultString);
            return true;
        }
        return false;
    }

    private static boolean testEquals(int[] a, int[] b) {
        for (int i = 0; i < 4; i++) {
            if (a[i] != b[i]) {
                return false;
            }
        }
        return true;
    }

    private static int[] toIntArray(int a) {
        int[] result = new int[4];
        result[0] = a / 1000;
        result[1] = a % 1000 / 100;
        result[2] = a % 1000 % 100 / 10;
        result[3] = a % 10;
        return result;
    }

    private static int[] toIntArray(int a, int b) {
        int[] result = new int[4];
        result[0] = a / 10;
        result[1] = a % 10;
        result[2] = b / 10;
        result[3] = b % 10;
        return result;
    }

    private static int[] sort(int[] source) {
        if (source == null || source.length != 4) {
            throw new RuntimeException("source int [] error");
        }
        int temp = 0;
        for (int i = 0; i < 4; i++) {
            for (int j = i; j < 4; j++) {
                if (source[j] < source[i]) {
                    temp = source[j];
                    source[j] = source[i];
                    source[i] = temp;
                }
            }
        }
        return source;
    }
}