public class ShuCha {
    int cha;
    int jie(int x,int y){
        cha=x-y;
        return cha;
    }

}
public class ShuHe {
    int he;
    int jia(int x,int y){
        he=x+y;
        return he;
    }

}

public class YunShuang {
  public static void main(){
      int x1=9,y2=8;
      ShuHe a=new ShuHe();
      ShuCha b=new ShuCha();
      int c,d;
      c=a.jia(x1,y2);
      d=b.jie(x1,y2);
      System.out.println(c);
      System.out.println(d);
      
  }
}

自己已经发现错误了
 public static void main(String []args){

恩恩，多多指教哦。