createOperate方法不能被声明为静态;静态方法只能在静态或顶级类型中声明

Question

public class Welcome { 
    public class OperationFactory { 

     public static Operation createOperate(String operate) { 
      Operation operation = null; 
      if("+".equalsIgnoreCase(operate)) { 
       operation = new OperationAdd(); 
      }else if("-".equalsIgnoreCase(operate)) { 
       operation = new OperationSub(); 
      }else if("*".equalsIgnoreCase(operate)) { 
       operation = new OperationMul(); 
      }else { 
       operation = new OperationDiv(); 
      } 
      return operation; 
     } 
    } 
} 

问题是：方法createOperate不能声明为静态;静态方法只能在静态或顶级类型中声明 我不知道如何解决。谢谢

Answer 1

由于错误信息中明确指出，你有3种选择：

1. 变化createOperate方法是非静态
2. 变化OperationFactory类是静态
3. 动静态方法createOperate至封闭Welcome类