interface InterfNumList {
int getNextNum (); //  獲取下一個數的值
void setFirstNum(); //  初始化變量start、val
void pointNum(int x); //  設置某點的數值，即給val重新賦值。
}
class MultThree implements InterfNumList {
  int start;
  int val;
  MultThree() {
    start = 1;
    val = 1;
  } 
  public int getNextNum() {
    val *= 3;
    return val;
  }
  public void setFirstNum() {
    start = 1;
    val = 1;
  }
  public void pointNum(int x) {
    start = x;
    val = x;
  }
}
class MultFour implements InterfNumList {
  int start;
  int val;
  MultFour() {
    start = 1;
    val = 1;
  } 
  public int getNextNum() {
    val *= 4;
    return val;
  }
  public void setFirstNum() {
    start = 1;
    val = 1;
  }
  public void pointNum(int x) {
    start = x;
    val = x;
  }
}
class InterfNumListDemo2 {
  public static void main(String args[]) {
    MultThree threeOb  = new MultThree();
    MultFour  fourOb= new MultFour();
    InterfNumList ob;
    for(int i=0; i < 4; i++) {
      ob = threeOb;
      System.out.println("Next MultThree value is " + 
                          ob.getNextNum()); 
      ob = fourOb;
      System.out.println("Next MultFour value is " +
                          ob.getNextNum());
    }
  }
}