Option is a good thing that most people really don't know how to use!

Tech 2023-07-14 14:11:54 Source: Network

OverviewNullPoInterException, ChInese name:Null poInter exceptionNPE, also known as NPE, is one of the most common error anomalies In software systems.Long ago, the Google Guava project IntroducedOptionalNull poInter exceptionNullTo expect programmers to write code that is both neat and more readable

Overview

NullPoInterException, ChInese name:Null poInter exceptionNPE, also known as NPE, is one of the most common error anomalies In software systems.

Long ago, the Google Guava project IntroducedOptionalNull poInter exceptionNullTo expect programmers to write code that is both neat and more readable.

OptionalNull

The followIng is a common parameter Null detection code, with an example as follows.

//DetermIne If the admInistrative region is emptyIfCountry!=Null{//DetermIne whether the admInistrative city is empty at the upper level of the admInistrative districtIfCountry. GetCity!=Null{//DetermIne whether the admInistrative provInce is empty at the upper level of the admInistrative cityIfCountry. GetCity. GetProvInce!=Null{//ObtaIn data related to the correspondIng admInistrative provInceReturnCountry. GetCity. GetProvInce. GetName}}}

This is still the most common three-layer judgment. If there is a large section of busIness logic processIng, you will fInd that the code not only looks bulky, but also dIfficult to read and has poor readability!

Optional source code diagram

If adjusted to useOptionalTo write it, it can be converted to the followIng notation:

//StrIngresult=Optional. of NullableCountry.MapCountry::GetCity.MapCity::GetProvInce.MapProvInce::GetName.OrElseError

adoptOptionalAfter programmIng, should the readability and cleanlIness of the entire code be much cleaner!

API Introduction

In JDK8, Option has a total of 12 core methods, let's take a look at their usage toGether!

2.1. empty

The empty method Returns an Optional Instance that does not contaIn a Value. It is meanIngless to use it alone and is maInly used In conjunction with other methods.

OptionalOptional=Optional. emptySystem. OutPrIntlnOptional--Optional. empty

2.2of

of Optional Null poInter exception.

//OptionalOptional=Optional.of"HelloWorld"System. OutPrIntlnOptional--Optional[HelloWorld]//Null poInter exceptionOptionalOptional=Optional.ofNullSystem. OutPrIntlnOptional--ExceptionInthread"maIn"java.lang.NullPoInterExceptionatjava.util.Objects.requireNonNullObjects. java:two hundred and threeatjava.util.Optional.<Init>Optional. java:nInety-sixatjava.util.Optional.ofOptional. java:one hundred and eight

2.3Of Nullable

The Of Nullable method will Return an Optional Instance, and If the passed In Value is not empty, it will Return an object contaInIng the specIfied Value; If Null is passed In, an empty object withOut any Values will be Returned, which is the first IntroducedOptional. emptyObject.

//OptionalOptional=Optional. of Nullable"HelloWorld"System. OutPrIntlnOptional--Optional[HelloWorld]//emptyOptionalOptional=Optional. of NullableNullSystem. OutPrIntlnOptional--Optional. empty

2.4isPresent

The isPresent method is used to determIne whether an Instance contaIns a Value. If it contaIns a non Null Value, it Returns True, otherwise it Returns False.

//Truebooleanrs1=Optional. of NullableHello.isPresentSystem.Out.PrIntlnrs1//Falsebooleanrs2=Optional. of NullableNull.isPresentSystem.Out.PrIntlnrs2--TrueFalse

2.5Get

The Get method Returns the current Value If the Instance contaIns non Null Values; Otherwise, a NoSushElementException exception will be thrown.

//Objectrs=Optional. of Nullable"HelloWorld".GetSystem.Out.PrIntlnrs--HelloWorld//NoSushElementExceptionObjectrs=Optional. of NullableNull.GetSystem.Out.PrIntlnrs--ExceptionInthread"maIn"java.util.NoSuchElementException:NoValuepresentatjava.util.Optional.GetOptional. java:one hundred and thirty-five

2.6IfPresent

IfPresent Consumer.

Optional. of Nullable"HelloWorld".IfPresentx->{System.Out.PrIntlnx}--HelloWorld

2.7filter

The filter method is used to filter Out values that do not meet the criteria and receive aPredicateParameter, If the condition is met, will Return the currentOptionalInstance, otherwise Return empty Instance.

Optional. of Nullable"HelloWorld". filterx->x.contaInsHello.IfPresentx->{System.Out.PrIntlnx}--HelloWorld

2.8Map

The Map method is the core method for chaIn callIng to avoid Null poInters. When an Instance contaIns a value, the passed In method is executed on the valueFunctionFunction Interface method and Returns a New value representIng the result valueOptionalInstance, which means repackagIng the Returned results asOptionalObject.

Optional. of Nullable"Hello+World".Mapt->{Ift.contaIns+{Returnt.replace+,""}Returnt;}.IfPresentt->{System.Out.PrIntlnt}--HelloWorld

2.9flatMap

The flatMap method is similar to the Map method, with the only dIfference beIng that:The Returned value needs to be manually wrapped asOptionalInstance, and parameter value cannot be empty.

Optional. of Nullable"Hello+World".flatMapt->{Ift.contaIns+{t=t.replace+,""}//ReturnOptional.oft}.IfPresentt->{System.Out.PrIntlnt}--HelloWorld

2.tenOrElse

OrElse .

Objectrs=Optional. of NullableNull.OrElse"Null"System.Out.PrIntlnrs--Null

2.11OrElseGet

The OrElseGet method Returns a non Null value if the Instance contaIns it; Otherwise, it will execute theSupplier.

Objectresult=Optional. of NullableNull.OrElseGet->{ReturnError;}System. OutPrIntlnresult--error

2.12OrElseThrow

OrElseThrow .

Optional. of NullableNull.OrElseThrow->NewRuntimeExceptionArgument is empty--ExceptionInthread"maIn"java.lang.RuntimeException:atcom.x.x.x.x.OptionalTest.lambda$maIn$tenOptionalTest3. java:one hundred and forty-fouratjava.util.Optional.OrElseThrowOptional. java:two hundred and ninety

How should Option be used

Optional . Optional Serializable.. Optional Jackson Optional Object.Jackson Null. jackson-modules-java8 .Optional .Optional Optional API.

Summary

The above is the newly added JDK8OptionalSummary of commonly used methods for classes, whereOf NullableMapandOrElse.

in additionOrElseOrElseGetOrElseThrowThe differences are as follows:

OrElseIf the instance contains a null value, return the specified value passed in
OrElseGetIf the instance contains a null value, return the returned value from the passed in method
OrElseThrowIf the instance contains null values, return the specified exception type

adoptOptionalTo solve the problemNPEException code is more elegant, such as the current object being relatively simple, which is a simple judgmentobj != Null.

andand.

#Headline Creation Challenge # # Java#

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