Arraylist size()==0,null,isEmpty()的区别

本文探讨了判断集合是否为空的方法,包括使用isEmpty和size>0两种方式,并解释了这两种方式的区别及应用场景。此外还介绍了如何判断集合是否已被实例化。

今天看到一段代码


查阅了下资料。

其实isEmpty和Size>0是等价的。都是判断集合里元素个数是否为空。

而null。是用来判断集合里是否实例化 了。

最终数据 signOffVo = {SignOffVo@12364} "SignOffVo(tbMlcsFormData=TbMlcsFormData(id=167, caseNo=MLCSCP202507310001, sys=null, fabBu=CP, caseType=0, realFabBu=, status=Active, applicant=JE15168, orgDescription=SJSEMI\IT\IT\SHMES/MESD, costCenter=null, flowType=1, equipmentType=CTH, expectTime=Fri Aug 01 00:00:00 GMT+08:00 2025, expectUsageHours=100, purposeCode=Customer borrow TE(TD2), projectCode=20221802, projectName=20220018-TWX TVXXX, po=, customerRequester=, borrowPurpose=3211133, targetEquipmentId=1111, executeTime=null, executeHours=null, planEquipmentId=null, realEquipmentId=null, setUpTime=null, setOffTime=null, borrowHours=null, returnToTmpgStatus=null, checkStatus=null, changeStatus=0, changeCode=, createUser=JE15168, createTime=Thu Jul 31 13:49:43 GMT+08:00 2025, updateUser=JE15168, updateTime=Thu Jul 31 13:49:43 GMT+08:00 2025, applicantName=JE15168, stepName=null, lotList=[TbMlcsLotData(id=118, mlcsId=167, lotId=56A950, vendorId=U202-CJ1, waferId=, updateUser=JE15168, updateTime=Thu Jul 31 13:49:43 GMT+08:00 2025" tbMlcsFormData = {TbMlcsFormData@12343} "TbMlcsFormData(id=167, caseNo=MLCSCP202507310001, sys=null, fabBu=CP, caseType=0, realFabBu=, status=Active, applicant=JE15168, orgDescription=SJSEMI\IT\IT\SHMES/MESD, costCenter=null, flowType=1, equipmentType=CTH, expectTime=Fri Aug 01 00:00:00 GMT+08:00 2025, expectUsageHours=100, purposeCode=Customer borrow TE(TD2), projectCode=20221802, projectName=20220018-TWX TVXXX, po=, customerRequester=, borrowPurpose=3211133, targetEquipmentId=1111, executeTime=null, executeHours=null, planEquipmentId=null, realEquipmentId=null, setUpTime=null, setOffTime=null, borrowHours=null, returnToTmpgStatus=null, checkStatus=null, changeStatus=0, changeCode=, createUser=JE15168, createTime=Thu Jul 31 13:49:43 GMT+08:00 2025, updateUser=JE15168, updateTime=Thu Jul 31 13:49:43 GMT+08:00 2025, applicantName=JE15168, stepName=null, lotList=[TbMlcsLotData(id=118, mlcsId=167, lotId=56A950, vendorId=U202-CJ1, waferId=, updateUser=JE15168, updateTime=Thu Jul 31 13:49:43 GMT+08:00 2025)])" signCaseVo = {SignCaseVo@12365} "SignCaseVo(actionNames=null, jyStatus=MPC, signers=CPMPC)" signOffHistory = {ArrayList@12350} size = 2 workCaseId = {Long@12392} 127 allFiles = {ArrayList@12358} size = 0 希望根据signOffHistory = {ArrayList@12350} size = 2 0 = {TbMlcsWorkCaseData@12432} "TbMlcsWorkCaseData(id=546, caseId=127, caseNo=MLCSCP202507310001, stepName=Create, action=urgentsubmit, comment=, createUser=JE15168, createTime=Thu Jul 31 13:49:43 GMT+08:00 2025, updateUser=JE15168, updateTime=Thu Jul 31 13:49:43 GMT+08:00 2025)" id = {Long@12435} 546 caseId = {Long@12392} 127 caseNo = "MLCSCP202507310001" stepName = "Create" action = "urgentsubmit" comment = "" createUser = "JE15168" createTime = {Date@12441} "Thu Jul 31 13:49:43 GMT+08:00 2025" updateUser = "JE15168" updateTime = {Date@12443} "Thu Jul 31 13:49:43 GMT+08:00 2025" 1 = {TbMlcsWorkCaseData@12355} "TbMlcsWorkCaseData(id=null, caseId=null, caseNo=null, stepName=MPC, action=null, comment=null, createUser=null, createTime=null, updateUser=JE03228;JE08611, updateTime=null)" id = null caseId = null caseNo = null stepName = "MPC" action = null comment = null createUser = null createTime = null updateUser = "JE03228;JE08611" updateTime = null updateUser去调用 userService.getFmUser(updateUser).getNickName() 数据为JE03228;JE08611则需要分组去调用循环两次JE03228;JE08611;JE05508 则是三次,以此类推
08-16
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