解法一：

import java.util.Scanner;

public class win {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int a = in.nextInt();
        int b = in.nextInt();
        int gcd=1;
        int r;
        while(b>0)
        {
            r=a%b;
            a=b;
            b=r;
        }
        System.out
 
.println(a);
    }
}

解法二：

import org.junit.Test;

/**
 * 求兩個數的最大公約數，，最小公倍數LCM(m,n) = m*n - GCD(m,n) 
 * @author Administrator
 *
 */

public class GCD {

    //GCD遞迴求法
    public int getGCD01(int m , int n) {
//      int a = Math.max(m, n);
//      int b = Math.min(m, n);
//      m = a;
//      n = b;
//      if ( m % n == 0)
 

//          return n;
//      else{
//          int temp = m % n;//除數
//          m = n;
//          getGCD01(m,temp);
//      }
//      return b;
        return m>=n?m%n==0?n:getGCD01(n,m%n):n%m==0?m:getGCD01(m,n%m);
    }

    //GCD遞推求法
    public int getGCD02(int m , int n){
        int r = 0;//餘數
        int max = Math.max(m, n);
        int
 
 min = Math.min(m, n);
        while(max % min != 0) {
            r = max % min;
            max = min;
            min = r;
        }
        return min;
    }

    //LCM
    public int getLCM(int m , int n){
        int gcd = getGCD01(m,n);
        int lcm = m*n/gcd;
        return lcm;
    }


    @Test
    public void testGCD01(){
        System.out.println( getGCD01(100,44) );
        System.out.println( getGCD01(100,44) );
    }
    @Test
    public void testGCD02(){
        System.out.println( getGCD02(100,44) );
        System.out.println( getGCD02(44,100) );
    }
    @Test
    public void testLCM(){
        System.out.println( getLCM(100,44) );
    }
}