创建类对象来进行阶乘递归？

我被分配了一个问题，使用递归编写程序，这是正常工作，我唯一的问题是它被指定创建一个类对象来进行析因计算而不是方法…我这样做对吗？

import java.util.*; import java.io.*; public class Assignment2A { public static void main(String[] args){ Scanner scan = new Scanner(System.in); //sets up scanner boolean correct = true; //sets up boolean operation while(true){ try{ //try catch operation System.out.println("Welcome to the factorial function"); System.out.println("Please enter a number or press 0 to exit"); long startTime =System.nanoTime(); System.out.println("Start Time: "+startTime+" nanoseconds."); //display the start time int n = scan.nextInt(); //scans the input int factorial= fact(n); System.out.println("The Factorial of the number entered is: " + factorial); long taskTime = System.nanoTime() - startTime; System.out.println("Task Time: "+taskTime+" nanoseconds.\n\n"); }catch(Exception e){ //checks if the input is a string or character System.out.println("That is not a number!"); //displays that the input is invalid long startTime =System.nanoTime(); long taskTime = System.nanoTime() - startTime; System.out.println("Task Time: "+taskTime+" nanoseconds."); System.exit(0); //exits the program } } } static int fact(int n){ int output; //sets the output as int long startTime = System.nanoTime(); //gets the start time of the cpu long taskTime = System.nanoTime()-startTime; //gets the task time if (n==0){ //if the input is 0, system exits System.out.println("Exiting Program"); System.out.println("Task Time: "+taskTime+ " nanoseconds."); //displays cpu time System.exit(0); } else if(n==1){ return 1; //if input is 1, the factorial of 1 is 1 } output = fact(n-1)*n; //recursive method for factorial return output; } } 

Answer 1

不，你创建了一个计算阶乘的方法，事实（int n）。

您应该使用计算阶乘的方法创建一个新类。 将实例化该类的对象，然后，将从类对象调用计算阶乘的方法。

例：

 // outside the while loop instantiate your class object for // dealing with factorial computations Factorial factorial = new Factorial(); // inside the while loop, instantiate your method for // computing factorial of "n", invoking your factorial // computation method that is defined inside your class int result = factorial.computeFactorial(n); 

Answer 2

如果你想创建一个类对象，那么从你的方法中删除静态如果你使用动态编程方法来解决这个问题会更好。

 import java.util.*; import java.io.*; public class Assignment2A { public static void main(String[] args){ Assignment2A x = new Assignment2A(); x.askForOutput(); } int fact(int n){ int output; //sets the output as int long startTime = System.nanoTime(); //gets the start time of the cpu long taskTime = System.nanoTime()-startTime; //gets the task time if (n==0){ //if the input is 0, system exits System.out.println("Exiting Program"); System.out.println("Task Time: "+taskTime+ " nanoseconds."); //displays cpu time System.exit(0); } else if(n==1){ return 1; //if input is 1, the factorial of 1 is 1 } output = fact(n-1)*n; //recursive method for factorial return output; } public void askForOutput(){ Scanner scan = new Scanner(System.in); //sets up scanner boolean correct = true; //sets up boolean operation while(true){ try{ //try catch operation System.out.println("Welcome to the factorial function"); System.out.println("Please enter a number or press 0 to exit"); long startTime =System.nanoTime(); System.out.println("Start Time: "+startTime+" nanoseconds."); //display the start time int n = scan.nextInt(); //scans the input int factorial= fact(n); System.out.println("The Factorial of the number entered is: " + factorial); long taskTime = System.nanoTime() - startTime; System.out.println("Task Time: "+taskTime+" nanoseconds.\n\n"); }catch(Exception e){ //checks if the input is a string or character System.out.println("That is not a number!"); //displays that the input is invalid long startTime =System.nanoTime(); long taskTime = System.nanoTime() - startTime; System.out.println("Task Time: "+taskTime+" nanoseconds."); System.exit(0); //exits the program } } } } 

Answer 3

如果您希望将它放在一个单独的类中，只需将您的fact（）方法封装在一个新类中。 但请注意，您打印输出的时间不正确 – 它只是计算最终进入递归方法的时间。

 public class Factorial { public static int compute( int val ) { long startTime = System.nanoTime(); int result = fact( val ); long taskTime = System.nanoTime()-startTime; System.out.println("Task Time: "+taskTime+ " nanoseconds."); } protected static int fact( int val ) { if (n==1){ return val; } return fact(val-1)*val; } } 

然后在你的主要，

  int answer = Factorial.compute(value);