//MethodDemo.java
import java.util.Scanner;
public class MethodDemo.java
{
    public static void main(String[] args)
    {
        //录入数据
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入第一个数据：");
        int a = sc.nextInt();
        Scanner sca = new Scanner(System.in);
        System.out.println("请输入第二个数据");
        int b = sca.nextInt();

        int max = getMax(a,b);
        System.out.println("max:"+max);
        //构造方法
        public static int getMax(int a, int b) {
            if(a>b) {
                return a;
            } else return b;
        }
    }
}

也是，我刚发现是因为构造的方法写在了main方法里面了