Three java programming methods implement the Fibonacci sequence

Write a program to output the first 20 items of the Fibonacci sequence on the console, with 5 newlines for each item

//java programming: 3 ways to implement the Fibonacci sequence
// The first method is:

public class Demo2 { 
  //  define 3 Three variable method  
  public static void main(String[] args) { 
    int a = 1, b = 1, c = 0; 
    System.out.println(" Before the Fibonacci sequence 20 Items as follows: "); 
    System.out.print(a + "\t" + b + "\t"); 
    // Because there are two more in front 1 , 1  so i<=18 
    for (int i = 1; i <= 18; i++) { 
      c = a + b; 
      a = b; 
      b = c; 
      System.out.print(c + "\t"); 
      if ((i + 2) % 5 == 0) 
        System.out.println(); 
    } 
  } 
 
} 

//java programming: 3 ways to implement the Fibonacci sequence
// The second method is:

public class Demo3 { 
  //  Define array methods  
  public static void main(String[] args) { 
    int arr[] = new int[20]; 
    arr[0] = arr[1] = 1; 
    for (int i = 2; i < arr.length; i++) { 
      arr[i] = arr[i - 1] + arr[i - 2]; 
    } 
    System.out.println(" The front of the Fibonacci sequence 20 The items are as follows: "); 
    for (int i = 0; i < arr.length; i++) { 
      if (i % 5 == 0) 
        System.out.println(); 
      System.out.print(arr[i] + "\t"); 
    } 
  } 
 
} 

//java programming: 3 ways to implement the Fibonacci sequence
// 3 methods:

public class Demo4 { 
  //  Use recursive methods  
  private static int getFibo(int i) { 
    if (i == 1 || i == 2) 
      return 1; 
    else 
      return getFibo(i - 1) + getFibo(i - 2); 
  } 
 
  public static void main(String[] args) { 
    System.out.println(" The front of the Fibonacci sequence 20 Items as follows: "); 
    for (int j = 1; j <= 20; j++) { 
      System.out.print(getFibo(j) + "\t"); 
      if (j % 5 == 0) 
        System.out.println(); 
    } 
  } 
 
} 

This rabbit problem is essentially a Fibonacci sequence: 1 pair of rabbits, 1 pair of rabbits born every month from the birth of the third month, and 1 pair of rabbits born every month after the birth of the third month, if no rabbits die, what is the total number of rabbits per month ? , now from the variable, array, recursion 3 points of view to solve this puzzle, of course, there are other methods, the same 1 question with a variety of different ideas to think about the solution, but also the comprehensive use of knowledge of the exercise.