Question

作为Java编程的初学者，我正在查找一些Java代码。我发现了这个：

import java.util.Scanner;
class FibonacciSeries {

public static void main(String[] args) 
{
   Scanner s = new Scanner(System.in);
   System.out.print("Enter the value of the number upto which the sequence should continue: ");
   int n = s.nextInt();
   fibonacci(n);
}

public static void fibonacci(int n) {
   if (n == 0) {
       System.out.println("0");
   } else if (n == 1) {
       System.out.println("0 1");
   } else {
       System.out.print("0 1 ");
       int a = 0;
       int b = 1;
       for (int i = 1; i < n; i++) {
           int nextNumber = a + b;
           System.out.print(nextNumber + " ");
           a = b;
           b = nextNumber;
       }
   }
}
}

有人可以告诉我public static void fibonacci(int n)后到底发生了什么事吗？

Answer 1

理论上的一点点： Fibonacci number

    if (n == 0) {                     //if user insert 0 than print to console 0
        System.out.println("0");      
    } else if (n == 1) {              //if user insert 1 than print to console 0 1
        System.out.println("0 1");    
    }

    else {                            //for every other cases (2, 3,... x)
       System.out.print("0 1 ");      //print to console 0 1        
       int a = 0;                      
       int b = 1;                     //before cycle prepare two values 0 and 1         
       for (int i = 1; i < n; i++) {             //Cycle since i which starts on 1 passed condition "is lover than inserted value"
           int nextNumber = a + b;               //store value of 0 + 1 
           System.out.print(nextNumber + " ");   //print this stored value
           a = b;                                //Set value in b into to variable a
           b = nextNumber;                       //set stored value as b
       }                                         //Increment i plus 1 and repeat cycle
    }

所以最后你会有用户插入5.打印 0 1 和周期（0 + 1） 1 （1 +1） 2 （1 + 2） 3 方法循环结束时返回main。 5印刷0 1 1 2 3.就是这样。

Answer 2

定义斐波那契序列的另一种方法。我认为它更清楚。

public static void fibonacci(int n) {
    if (n == 0) {
        return 0;
    } else if (n == 1) {
      return 1;
    } else {
        return fibonacci(n-1) + fibonacci(n-2);
    }

}

Answer 3

您在此处看到的是algorithm that calculates fibonacci numbers的实施，最多为一定数量的数字n，加上数字0。

Fibonacci序列中的前两个数字是1和1，或0和1，具体取决于所选择的序列起点，后面的每个数字都是前两个数字的总和。

根据定义，这些数字序列以算法中的0和1开头。

if (n == 0) {
    System.out.println("0");
} else if (n == 1) {
    System.out.println("0 1");
}

这两个语句处理了用户输入0或1作为限制的可能性，并分别打印0或0 1。（那是System.out.println();的用途。）

第三种情况（如果输入既不是0也不是1）计算更长的序列：

else {
   System.out.print("0 1 ");                 //this statement prints the start "0 1 "
   int a = 0;                                //the two starting numbers a and b are initialized
   int b = 1;
   for (int i = 1; i < n; i++) {             //for the given amount of numbers:
       int nextNumber = a + b;               //calculate the next number as sum of both previous numbers
       System.out.print(nextNumber + " ");   //print this number
       a = b;                                //set the old b as new a
       b = nextNumber;                       //set the new number as b
   }                                         //repeat
}

因此，对于6的示例输入，输入else个案，打印
0 1 之后，for-each循环将运行5次，打印：
1，2，3，5，8

这是第一个n + 1个斐波纳契数。

对for语句如何工作有一个阅读here，以便更好地了解最新情况，但基本上它说：

for("start here"; "repeat as long as this condition is true"; "after each step do this")
{
    //Everything between the brackets will be executed once for every run through the loop.
}

让我们看看在计算样本时每次迭代时值的变化：

╔═══╦═══╦═══╦════════════╦═══════╦═══════╗
║ i ║ a ║ b ║ nextNumber ║ new a ║ new b ║
╠═══╬═══╬═══╬════════════╬═══════╬═══════╣
║ 1 ║ 0 ║ 1 ║          1 ║     1 ║     1 ║
║ 2 ║ 1 ║ 1 ║          2 ║     1 ║     2 ║
║ 3 ║ 1 ║ 2 ║          3 ║     2 ║     3 ║
║ 4 ║ 2 ║ 3 ║          5 ║     3 ║     5 ║
║ 5 ║ 3 ║ 5 ║          8 ║     5 ║     8 ║
╚═══╩═══╩═══╩════════════╩═══════╩═══════╝

Fibonnaci序列

3 个答案: