public class Smp11
{
    public static void main(String args[])
    {
        Ko lkl = new Ko();
        lkl.intiko();
    }
    
}

class Score
{
    int enGrade;
    
    public void setEn(int enGrade)
    {
        this.enGrade = enGrade;
    }
}

class Ko
{
    Score stug[] = new Score[3];
    
    public void intiko()
    {
        //需要先给数组中的元素赋值
        stug[0] = new Score();
        stug[1] = new Score();
        stug[2] = new Score();
        
        stug[0].setEn(0);
        stug[1].setEn(1);
        stug[2].setEn(2);
    }
}

------解决方案--------------------
具体做法
Java code

public class smp11 {
public static void main(String args[])
{
ko lkl = new ko();
lkl.intiko();
}

}
class score
{
  int enGrade;
  public void setEn(int enGrade)
  {
this.enGrade=enGrade;   
  }
}
class ko
{
  score stug[] = new score[3];

  public void intiko()
  {  stug[0]=new score();
  stug[1]=new score();
  stug[2]=new score();
  stug[0].setEn(0);
  stug[1].setEn(1);
  stug[2].setEn(2);
  }
}

------解决方案--------------------
那是因为你没有实例化score.你定义了score为3的数组类型，却忽略了实例，必须报错，这样再实例一下就行了。
Java code

public class smp11 {
    public static void main(String args[])
    {
    ko lkl = new ko();
    lkl.intiko();
    }

    }
    class score
    {
      int enGrade;
      public void setEn(int enGrade)
      {
         this.enGrade=enGrade;   
      }
    }
    class ko
    {
      int len=3;
      score[] stug = new score[len]; 
      public void intiko()
      {
          for(int i=0;i<len;i++)
          {
              stug[i]=new score();
          }
          stug[0].setEn(0);
          stug[1].setEn(1);
          stug[2].setEn(2);
      }
    }