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Troubleshooting and resolving problems when using LiveData

This article aims to help developers solve the problem that when using LiveData, the value of LiveData is updated from the callback function, but the observer cannot receive the update event. The article will analyze the cause of the problem in depth and provide solutions based on setValue() and postValue() to ensure that LiveData can also pass data correctly in a multi-threaded environment.

Sep 04, 2025 am 11:57 AM

Add custom token authorization for specific endpoints in Spring OAuth2 resource server

This document explains how to implement a custom Token authorization scheme for specific endpoints in Spring OAuth2 resource server. This highlights the use of JWT (JSON Web Token) to add custom authorization information to the token through Keycloak configuration and verify it on the resource server side. At the same time, it is also discussed how to use Client Credentials Flow to authorize trusted clients.

Sep 04, 2025 am 11:24 AM

Correct pose for Java subclass to access private variables of parent class

This article aims to guide Java developers to access and utilize private variables of the parent class in subclasses without modifying the parent class code. We will explore effective ways to indirectly access private variables through inheritance and method rewriting, as well as using public methods provided by the parent class, and provide code examples to help readers understand and master these techniques, so that they can be flexibly used in actual development.

Sep 04, 2025 am 11:09 AM

Analysis of the core mechanism of Java HashMap in Two Sum problems

This article discusses the application of HashMap in solving Two Sum problems in depth, and pays particular attention to the behavior of the HashMap.containsKey() method on initially empty maps. The article explains the basic principle of containingKey() to return false to empty HashMap, and analyzes in detail how the Two Sum algorithm can efficiently find the target difference value and realize a linear time complexity solution by dynamically filling HashMap during the iteration process.

Sep 04, 2025 am 11:00 AM

Mockito Verify failure and internal dependency simulation analysis in Java unit test

This article explores in-depth common reasons for verification failure in Mockito unit tests, especially when the object being tested creates its dependencies internally. The article details how to use Mockito's spy function combined with doReturn().when() to simulate these internally created dependencies to ensure the correctness of the test. At the same time, it also covers alternatives to MockitoAnnotations.initMocks, the difference between spy and InjectMocks, and the use scenarios of PowerMock, aiming to provide a comprehensive set of Java unit testing best practices.

Sep 04, 2025 am 10:57 AM

Java uses regular expressions to replace the contents of a specific string

This article details how to elegantly replace strings followed by specific keywords in text in Java. By using the String.replaceFirst() method combined with concise regular expressions, this requirement can be achieved efficiently and clearly, avoiding writing verbose and complex code. The tutorial will deeply analyze the construction of regular expressions and their skills in practical applications, helping developers easily handle text replacement tasks.

Sep 04, 2025 am 10:27 AM

How to pass this to Supplier in Java

This article discusses how to pass the current object this to the Supplier interface in a Java 8 environment. For scenarios like CompleteFuture.completeAsync(), the differences in passing this using Lambda expressions and method references are analyzed, and their potential performance impact is discussed. Ultimately, the rationality of using this directly in most cases is explained, avoiding unnecessary complexity.

Sep 04, 2025 am 10:18 AM

Convert the current time to seconds in Java

This article describes how to convert the current time to seconds starting from the day in Java and provides sample code using the java.time.LocalTime class. Get the current time through LocalTime.now() and convert it to seconds using the toSecondOfDay() method. At the same time, it also introduces how to deal with time zone issues and how to define target time in a more readable way.

Sep 04, 2025 am 10:06 AM

Java 9: ??Use regular expressions to efficiently count the number of occurrences of multiple substrings in strings and compare them

This tutorial explores how to do in Java, especially in Java 9 and later, there is no need to explicitly loop through the occurrence of specific substrings (such as "cat" and "dog") in a string and compare whether they are equal. The core method is to use the results().count() functions of java.util.regex.Pattern and Matcher classes to achieve concise and efficient code and improve development efficiency.

Sep 04, 2025 am 09:33 AM

How to use interfaces in Java

Interfaces are used in Java to define contracts that classes must follow, and support abstract, polymorphic and loosely coupled designs; 1. Use the interface keyword to declare interfaces, including abstract methods, default methods, static methods and constants; 2. Classes implement interfaces through implementations and provide specific implementations of abstract methods; 3. A class can implement multiple interfaces to support multiple behaviors; 4. The default methods in the interface provide default implementations, and static methods can be called directly through the interface; 5. The interface variable is default to publicstaticfinal and used as constants; 6. The interface is suitable for defining behavior, decoupling, callback mechanisms and unit tests across unrelated classes; therefore, the rational use of interfaces can improve the modularity, reusability and maintainability of the code.

Sep 04, 2025 am 09:20 AM

java interface

What is the difference between a Set and a List in Java?

Set does not allow duplicate elements and usually does not guarantee order, while List allows duplicates and maintains insertion order; therefore, Set is used when uniqueness and frequent searches are required, and List is used when index access and repetitive values ??are required. The specific performance depends on the implementation class such as ArrayList supports fast random access, and HashSet provides average O(1) addition and search efficiency.

Sep 04, 2025 am 09:15 AM

How to use PreparedStatement in Java

The steps to use PreparedStatement are: 1. Establish a database connection; 2. Create a PreparedStatement containing a placeholder; 3. Set parameter values ??using setString, setInt and other methods (the index starts from 1); 4. Call executeUpdate() or executeQuery() according to the SQL type to execute statements; 5. Use try-with-resources to automatically close the Connection, PreparedStatement and ResultSet resources, thereby preventing SQL injection, improving performance and ensuring that resources are properly released.

Sep 04, 2025 am 09:14 AM

Configuring Java 19 preview and incubator features in Gradle project

This article provides detailed instructions on how to enable Java 19 preview (such as virtual threads) and incubator (such as structured concurrency) features in Gradle projects. By configuring compileJava tasks' compiler parameters and application plug-in's JVM startup parameters, developers can seamlessly integrate and experience new features of the Java platform, ensuring that these experimental APIs are correctly identified and used during the compilation and run phases. This will involve setting key command line flags such as --release, --enable-preview, and --add-modules to suit the needs of different stages. This tutorial is designed to provide clear and actionable steps to help you explore Java in a Gradle environment

Sep 04, 2025 am 08:48 AM

How to create a two-dimensional array in Java

There are three main ways to create two-dimensional arrays in Java: 1. Use fixed size and initialize the default value, such as int[][]array=newint[3][4]; to create an array of 3 rows and 4 columns, the elements default to 0; 2. Initialize the specified value directly, such as int[][]array={{1,2,3},{4,5,6},{7,8,9}}; to create a 3x3 two-dimensional array and assign values; 3. Create an irregular (jagged) array, such as int[][]raggedArray={{1,2},{3,4,5,6},{7}};, each row length can be different; elements can be accessed or modified through array[i][j], and use nested for loops or

Sep 04, 2025 am 08:45 AM