Java编程计算兔子生兔子的问题

public class exp2{  public static void main(String args[]){    int i=0;    for(i=1;i<=20;i++)      System.out.println(f(i));  }  public static int f(int x)  {    if(x==1 || x==2)      return 1;    else      return f(x-1)+f(x-2);  }}

public class exp2{  public static void main(String args[]){    int i=0;    math mymath = new math();    for(i=1;i<=20;i++)      System.out.println(mymath.f(i));  } }class math{  public int f(int x)  {    if(x==1 || x==2)      return 1;    else      return f(x-1)+f(x-2);  }}