createOperate方法不能声明为static;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static;静态方法只能在静态或顶级类型中声明 我不知道该如何解决。谢谢

Answer 1

正如错误消息明确指出的那样，您有3个选项：

1. 将createOperate方法更改为非静态
2. 将OperationFactory类更改为静态
3. 将静态方法createOperate移至封闭的Welcome类