What is an abstract class in java? abstract class declaration

Common JavaAPM tools include NewRelic, DatadogAPM, AppDynamics, SkyWalking, Pinpoint and Prometheus Grafana Micrometer combinations; whether APM is required depends on system lag, complex microservice calls, performance details and optimization requirements; APM should consider deployment methods, learning costs, performance impact, cost and integration capabilities; when using them, you should pay attention to reasonable configuration, sampling rate, alarm rules, and analyze the root cause in combination with code.

1.RxJava is a responsive framework based on observer pattern and functional programming, suitable for handling asynchronous and non-blocking tasks. 2. Core types include Observable, Flowable, Single, etc., which are used to represent different forms of data flow. 3. Data conversion and combination are performed through operators such as map, filter, and flatMap to simplify complex logic. 4. Use Schedulers.io(), Schedulers.computation(), AndroidSchedulers.mainThread() and other schedulers to control thread switching. 5. Specify the data flow start thread through subscribeOn, obse

When using double check lock to implement lazy loading singletons, the volatile keyword is required to ensure thread visibility and prevent instruction re-arrangement; 2. It is recommended to use static internal classes (BillPugh scheme) to implement thread-safe lazy loading singletons, because the JVM ensures thread safety and no synchronization overhead; 3. If you do not need lazy loading, you can use static constants to implement simple and efficient singletons; 4. When serialization is involved, enumeration method should be used, because it can naturally prevent multiple instance problems caused by reflection and serialization; in summary, general scenarios prefer static internal classes, and serialized scenarios to select enumerations. Both have the advantages of thread safety, high performance and concise code.

Kotlinoffersthebestbalanceofbrevityandreadability,Javaisverbosebutpredictable,andScalaisexpressivebutcomplex.2.Scalaexcelsinfunctionalprogrammingwithfullsupportforimmutabilityandadvancedconstructs,KotlinprovidespracticalfunctionalfeatureswithinanOOPf

UseMavenorGradleconsistentlywithcentralizedversionmanagementandBOMsforcompatibility.2.Inspectandexcludetransitivedependenciestopreventconflictsandvulnerabilities.3.EnforceversionconsistencyusingtoolslikeMavenEnforcerPluginandautomateupdateswithDepend

The two core features of Java8 are Lambda expressions and StreamsAPI, which make the code more concise and support functional programming. 1. Lambda expressions are used to simplify the implementation of functional interfaces. The syntax is (parameters)->expression or (parameters)->{statements;}, for example (a,b)->a.getAge()-b.getAge() instead of anonymous internal classes; references such as System.out::println can further simplify the code. 2.StreamsAPI provides a declarative data processing pipeline, the basic process is: create Strea

SecurityToken is used in Java applications for authentication and authorization, encapsulating user information through Tokenization to achieve stateless authentication. 1. Use the jjwt library to generate JWT, select the HS256 or RS256 signature algorithm and set the expiration time; 2. Token is used for authentication, Encryption is used for data protection, sensitive data should be encrypted using AES or RSA, and passwords should be stored with hash salt; 3. Security precautions include avoiding none signatures, setting the expiration time of tokens, using HTTPS and HttpOnlyCookies to store tokens; 4. In actual development, it is recommended to combine SpringSecurity and

var was introduced in Java 10 for local variable type inference, to determine the type during compilation, and maintain static type safety; 2. It can only be used for local variables in methods with initialized expressions, and cannot be used for fields, parameters or return types; 3. Non-initialization, null initialization and lambda expression initialization are prohibited; 4. It is recommended to use them when the type is obvious to improve simplicity and avoid scenarios that reduce readability. For example, types should be explicitly declared when complex methods are called.