有1、2、3、4四个数字，输出它们所组成的所有互不相同且无重复数字的三位数，并统计总个数。

       public class ExamDemo {

              public static void main(String[] args) {

                     int count = 0;

                     for(int x=1; x<5; x++) {

                            for(int y=1; y<5; y++) {

                                   for(int z=1; z<5; z++) {

                                          if(x != y && y != z && x != z) {

                                                 count ++;

                                                 System.out.println(x*100 + y*10 + z );

                                          }

                                   }

                            }

                }

                     System.out.println("共有" + count + "个三位数");