public class 笛卡尔积生成SKU {
    private static String[] aa={"a1","a2"};
    private static String[] bb={"b1"};
    private static String[] cc={"c1","c2","c3"};
    private static String[] dd={"d1","d2"};
    private static String[][] xyz={aa,bb,cc,dd};
    private static int counterIndex =xyz.length-1;
    private static int[] counter={0,0,0,0};

    public static void main(String[] args) {
        int myLength=aa.length*bb.length*cc.length*dd.length;
        for (int i=0;i<myLength;i++){
            System.out.print(aa[counter[0]]);
            System.out.print("\t");
            System.out.print(bb[counter[1]]);
            System.out.print("\t");
            System.out.print(cc[counter[2]]);
            System.out.print("\t");
            System.out.print(dd[counter[3]]);
            System.out.println();
            handle();
        }
    }
    public static void handle(){
        counter[counterIndex]++;
        if (counter[counterIndex]>=xyz[counterIndex].length){
            counter[counterIndex]=0;
            counterIndex--;
            if (counterIndex>=0){
                handle();
            }
            counterIndex=xyz.length-1;
        }
    }
}

结果： 

a1	b1	c1	d1
a1	b1	c1	d2
a1	b1	c2	d1
a1	b1	c2	d2
a1	b1	c3	d1
a1	b1	c3	d2
a2	b1	c1	d1
a2	b1	c1	d2
a2	b1	c2	d1
a2	b1	c2	d2
a2	b1	c3	d1
a2	b1	c3	d2