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;
  }
}
public class InterfNumListDemo {
  public static void main(String args[]) {
    MultThree ob = new MultThree();
    for(int i=0; i < 4; i++)
      System.out.println("Next number  is " +
                         ob.getNextNum());
						
    System.out.println();		
    ob.setFirstNum();                           //返回初始值
    for(int i=0; i < 4; i++)
      System.out.println("Next number is " +
                         ob.getNextNum());
    System.out.println("\n Starting at 10");
    ob.pointNum(10);                          //設置某點的值，即為val賦值
    for(int i=0; i < 4; i++)
      System.out.println("Next number is " +
                         ob.getNextNum());
  }
}