Java继承：方法集（List <bean>）不适用于参数ArrayList <subbean> </subbean> </bean>

Question

我在下面收到错误。

层次结构： GeneralBudgetBean - ＆gt; RRBudgetBean

它们包含具有以下层次结构的数据成员： GeneralBudgetYearBean - ＆gt; RRBudgetYearBean

父类 - GeneralBudgetBean.java

// Data member
private List<GeneralBudgetYearBean> budgetYearBeans;

// Getters/setters
    public List<GeneralBudgetYearBean> getBudgetYearBeans() {
        return budgetYearBeans;
    }

    public void setBudgetYearBeans(List<GeneralBudgetYearBean> budgetYearBeans) {
        this.budgetYearBeans = budgetYearBeans;
    }

扩展类 - RRBudgetBean.java

public class RRBudgetBean extends GeneralBudgetBean {
   //...

   public void initRRBudgetBean()
   {
       this.setBudgetYearBeans(new ArrayList<RRBudgetYearBean>());
   }

}

错误：

The method setBudgetYearBeans(List<GeneralBudgetYearBean>) in the type GeneralBudgetBean is not applicable for the arguments ArrayList<RRBudgetYearBean>

换句话说，错误是：

Method method(List<Bean>) not applicable for arguments ArrayList<SubBean>.

Answer 1

从教程（http://docs.oracle.com/javase/tutorial/java/generics/inheritance.html）： Box<Integer>和Box<Double>不是Box<Number>的子类型。

在这种情况下，您必须将方法签名更改为

public void setBudgetYearBeans(List<? extends GeneralBudgetYearBean> budgetYearBeans) {
    this.budgetYearBeans = budgetYearBeans;
}

关于通配符的http://docs.oracle.com/javase/tutorial/java/generics/wildcardGuidelines.html文章可能有用。

Answer 2

更改您的

setBudgetYearBeans(List<GeneralBudgetYearBean> budgetYearBeans) 

到

setBudgetYearBeans(ArrayList<GeneralBudgetYearBean> budgetYearBeans)

通常，最好使方法参数类型更具体，并且方法返回值更一般。