How many three-digit numbers can be formed by using four numbers 1, 2, 3, and 4 to form non-repeating numbers?

public static void main(String[] args) {
  
  int sum=0;
  
  for (int i = 1; i < 5; i++) {
   for (int j = 1; j < 5; j++) {
    for (int k = 1; k < 5; k++) {
     if(i!=j&&k!=j&&i!=k){
      System.out.println(i+""+j+""+k);
      sum++;
     }
    }
   }
  }
  System.out.println("共有"+sum+"种");
 }