Generic method return type
Here's the Animal class:
public class Animal{
private Map<String,Animal> friends =new HashMap<String,Animal>();
public void addFriend(String name,Animal animal){
friends.put(name,animal);
}
public Animal callFriend(String name)
{return friends.get(name);}}
And here's some code snippet with lots of typecasting:
Mouse jerry =newMouse();
jerry.addFriend("spike",newDog());
jerry.addFriend("quacker",newDuck());
((Dog) jerry.callFriend("spike")).bark();
((Duck) jerry.callFriend("quacker")).quack();
Is there any way I can use generics for the return type to get rid of the typecasting, so that I can say
jerry.callFriend("spike").bark();
jerry.callFriend("quacker").quack();
Here's some initial code with return type conveyed to the method as a parameter that's never used.
public<T extendsAnimal> T callFriend(String name, T unusedTypeObj){return(T)friends.get(name);}
Answer==
public<T extendsAnimal> T callFriend(String name,Class<T> type){return type.cast(friends.get(name));}
Generic method return type的更多相关文章
- 一种封装Retrofit的方法,可以自动解析Gson,回避Method return type must not include a type variable or wildcard: retrofit2.Call<T>的问题
封装目的:屏蔽底层实现,提供统一接口,并支持Gson自动转化 最初封装: //请求方法 interface RequestListener { interface PostListener { @PO ...
- delete attempted to return null from a method with a primitive return type (int)
今天被自己给蠢死了 今天在代码中遇到这个错误, 百度翻译一下:映射方法,从一org.system.mapper.child.chmorganizationexaminationmapper.delet ...
- rg.apache.ibatis.binding.BindingException: Mapper method 'com.dao.Cameao.getOnlineDayRation attempted to return null from a method with a primitive return type (float)
本文为博主原创,未经允许不得转载: 异常展示如下: org.apache.ibatis.binding.BindingException: Mapper method 'com.dao.Cameao. ...
- mysql查询null异常:attempted to return null from a method with a primitive return type
select sum(deposit_amount)from tb_commission_ib_day mysql查询时报异常: attempted to return null from a met ...
- org.apache.ibatis.binding.BindingException: Mapper method 'attempted to return null from a method with a primitive return type (long).
一.问题描述 今天发现测试环境报出来一个数据库相关的错误 org.apache.ibatis.binding.BindingException: Mapper method 'attempted to ...
- [TypeScript] Infer the Return Type of a Generic Function Type Parameter
When working with conditionals types, within the “extends” expression, we can use the “infer” keywor ...
- attempted to return null from a method with a primitive return type (int).
java接口文件 package com.cyb.ms.mapper; import org.apache.ibatis.annotations.Param; public interface Acc ...
- Bean property ‘mapperHelper’ is not writable or has an invalid setter method. Does the parameter type of the setter match the return type of the getter?
spring boot 报错: Caused by: org.springframework.beans.NotWritablePropertyException: Invalid property ...
- Mapper method 'com.xxxx.other.dao.MyDao.getNo attempted to return null from a method with a primitive return type (int)
使用myBatis调用存储过程的返回值,提示错误信息: org.apache.ibatis.binding.BindingException: Mapper method 'com.xxxx.othe ...
随机推荐
- Shell基础:变量类型 & 运算符
Shell变量 Shell支持三种类型的变量 用户自定义变量:用户自定义的变量,变量名以英文字母或下划线开头,区分大小写. 位置变量:根据位置传递参数给脚本的变量,默认支持9个位置变量 $1,$2,$ ...
- Junit4入门
eclipse自带junit包,可右键直接新建junit类 静态引入:import static org.junit.Assert.* assert.*是类,静态引入会引入assert里的所有静态方法 ...
- 网络编程socket基本API详解(转)
网络编程socket基本API详解 socket socket是在应用层和传输层之间的一个抽象层,它把TCP/IP层复杂的操作抽象为几个简单的接口供应用层调用已实现进程在网络中通信. socket ...
- eclipse hibernate 插件测试1
今天先测试了hibernate tools 安装 在eclipse marketplace里面搜索 hibernate tools 就能找到 网上很多文章所说的使用 install new softw ...
- mouseover和mouseout多次触发解决方法(兼容ie和firefox)(转)
在用到mouseover和mouseout事件来作为事件触发的条件,但是如果我们用做触发的元素内部有其他的元素的时候当鼠标移上的时候会反复的触发mouseover和mouseout事件,如导致菜单闪烁 ...
- JS引用类型之——数组
前言 数组作为JS中非常常用的引用类型,其功能是非常强大滴,今天小猪就彻底的看了下它.为了防止猪脑子不够用所以记录在案呐 1.数组的创建 var arrayObj = new Array(); //创 ...
- 判断IE8
var browser=navigator.appName; var panduan_hide='style="display:none;"'; if(browser= ...
- S1 : 传递参数
ECMAScript 中所有函数的参数都是按值传递的.也就是说,把函数外部的值复制给函数内部的参数,就和把值从一个变量复制到另一个变量一样.基本类型值的传递如同基本类型变量的复制一样,而引用类型值的传 ...
- POJ 2159 Ancient Cipher 难度:0
题目链接:http://poj.org/problem?id=2159 #include <cstring> #include <cstdio> #include <cc ...
- PowerMock与EasyMock的应用(转)
Leader请求在做Junit测试的时辰,Mock掉各个办法之间的依附.这两天进修了下PowerMock的应用. PowerMock是EasyMock的一个扩大,参加了static,final,pri ...