Core Java 谈谈HashMap

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Core Java 谈谈HashMap

说起Java的HashMap相信大家都不是很陌生,但是对于HashMap内部结构有些同学可能不太了解,咱们下一步就将其展开. HashMap是基于Hash算法的,同理的还有HashSet和HashTable.我的一篇博文讲述了如果将Object作为Key的话,那么就需要注意重写其hashCode()和equals()方法,当然,这个equals()不是必要重写的,但是在Effective Java中这条是一条准则.那么针对这块有个问题,如果只写了hashCode方法不写equals或者反之呢?…

Core Java 谈谈 ThreadPoolExecutor

说起Java 7的Executors框架的线程池,同学们能想到有几种线程池,它们分别是什么? 一共有四个,它们分别是Executors的 newSingleThreadPool(), newCachedThreadPool(), newFixedThreadPool(),newScheduledThread(),四个静态方法,当然在java 8中还有一个newWorkStealingThreadPool(). 但今天这些这些不是咱们今天要说的重点,今天要说的重点是里边所使用的ThreadPool…

Core Java Interview Question Answer

This is a new series of sharing core Java interview question and answer on Finance domain and mostly on big Investment bank.Many of these Java interview questions are asked on JP Morgan, Morgan Stanley, Barclays or Goldman Sachs. Banks mostly asked c…

org.apache.ibatis.builder.IncompleteElementException: Could not find result map java.util.HashMap

这样的配置有问题吗? <select id="getFreightCollectManagementList" resultMap="java.util.HashMap" parameterType="com.rms.providers.dto.AccountingPayableDto"> 有的, 出现mybatis 错误: -- :: - [http-nio--exec-] DEBUG - Added HttpServletResp…

spring boot 之错误：SpelEvaluationException: EL1008E: Property or field 'timestamp' cannot be found on object of type 'java.util.HashMap'

这个错误我也见过很多次了,今天终于理解了其出现的原因. 错误是这样的: 2017-11-23 18:05:39.504 ERROR 4092 --- [nio-8080-exec-3] o.a.c.c.C.[Tomcat].[localhost] : Exception Processing ErrorPage[errorCode=0, location=/error] org.springframework.web.util.NestedServletException: Request pr…

Top 25 Most Frequently Asked Interview Core Java Interview Questions And Answers

We are sharing 25 java interview questions , these questions are frequently asked by the recruiters.Java questions can be asked from any core java topic . So we try our best to provide you the java interview questions and answers for experienced whic…

Difference Between Arraylist And Vector : Core Java Interview Collection Question

Difference between Vector and Arraylist is the most common Core Java Interview question you will come across in Collection . This question is mostly used as a start up question by the Interviewers before testing deep roots of the Collection .Vec…

java.lang.ClassCastException: java.util.HashMap cannot be cast to java.lang.String

问题背景:从前端传来的json字符串中取某些值,拼接成json格式入参调外部接口. 报如下错: java.lang.ClassCastException: java.util.HashMap cannot be cast to java.lang.String at com.taobao.hsf.proxy.bytecode.proxy31.registerCancellation(proxy31.java) at com.ohaotian.approval.controller.spzx.Te…

EL1008E: Property or field 'timestamp' cannot be found on object of type 'java.util.HashMap

2018-06-22 09:50:19.488 INFO 20096 --- [nio-8081-exec-2] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring FrameworkServlet 'dispatcherServlet'2018-06-22 09:50:19.488 INFO 20096 --- [nio-8081-exec-2] o.s.web.servlet.DispatcherServlet …