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Technical Articles

Java

javaTutorial

Analysis and solution of data inconsistency in ConcurrentHashMap in concurrent environment

This article aims to solve the problem of data inconsistent when using ConcurrentHashMap in concurrent environments due to the simultaneous writing of multiple threads. By analyzing the cause of the problem and providing a solution to ensure that all threads have completed execution and then check the Map size, helping developers avoid such concurrency problems and ensure data accuracy.

Aug 17, 2025 pm 01:12 PM

SpringBoot application startup failed: Port 8080 has been occupied Solution

This article provides detailed troubleshooting and resolution steps for common "Web server failed to start. Port 8080 was already in use." errors when starting Spring Boot projects. By using the netstat (Windows) or lsof (Unix/Linux/Mac) commands, processes that occupy port 8080 can be quickly located and actions such as stopping the process or configuring the Spring Boot application to use other ports to resolve startup failures.

Aug 17, 2025 pm 01:09 PM

Efficient comparison of two string lists in Java: from linear search optimization to collection operations

This article aims to guide readers how to efficiently compare two ArrayLists to determine whether all elements in one list exist in another. We will start with the basic linear search method, analyze its limitations, and then introduce and recommend a search strategy optimized using HashSet to significantly improve comparison efficiency. In addition, the tutorial will cover how to correctly handle user dynamic input and provide complete code examples and practical considerations.

Aug 17, 2025 pm 12:51 PM

What is the significance of the public static void main(String[] args) method in Java?

public: Ensure that the JVM can access the method from the outside; 2.static: Make the method belongs to a class rather than an instance, and can be called without creating an object; 3.void: means that the method does not return any value; 4.main: is the fixed entry method name recognized by the JVM; 5.String[]args: is used to receive command line parameters, so that the program has the flexibility of external input. Therefore, publicstaticvoidmain(String[]args) is a necessary entry point for Java applications. The JVM relies on its standard signature to start the program. The lack or error definition will cause a "Mainmethodnotfound" error and the program cannot run.

Aug 17, 2025 pm 12:35 PM

java main method

Spark: Remove columns from beans before partition writing

This article describes how to flexibly remove unwanted columns from Java Beans when using Spark for data partition writing to avoid errors caused by data source format limitations. By using the select operation before writing, you can dynamically select the required columns, thereby achieving flexible processing of different partition combinations and avoiding the creation of multiple bean classes.

Aug 17, 2025 pm 12:33 PM

Optimizing nested loops with HashMap: Java object list conversion

This article aims to explain how to optimize the performance of nested loops in Java using HashMap, especially when it comes to comparing properties of two object lists. By converting a list to a HashMap, it can significantly reduce time complexity and improve code execution efficiency. This article will provide detailed steps and code examples to help readers understand and apply this optimization technique.

Aug 17, 2025 pm 12:30 PM

Strategies and practices for efficiently and concurrently executing a large number of Linux commands in Java applications

This article explores strategies for efficiently and concurrently executing a large number of Linux commands such as socat in Java applications. The core is to use ProcessBuilder and thread pool to manage concurrent processes, and avoid I/O blocking by asynchronously processing or redirecting output streams. The article emphasizes that it is feasible to successfully run thousands of lightweight, long-lifetime commands, and the key lies in optimizing resource management and output processing, rather than the number of commands itself.

Aug 17, 2025 pm 12:24 PM

Build Google Maps navigation URL with Java and open automatically

This tutorial details how to use Java programming to construct a specific Google Maps URL to automatically open and display route navigation between the two places in the user's default browser. This approach avoids complex mouse and keyboard simulations and provides a simple and efficient solution for designating any global city as a starting point and end point.

Aug 17, 2025 pm 12:18 PM

How to read user input from the console in Java

Using the Scanner class is a common method for reading console input in Java, which is suitable for reading basic types such as strings and integers; 2. Pass System.in when creating Scanner objects, and read different types of inputs through nextLine(), nextInt() and other methods; 3. Note that after calling nextInt() and other methods, nextLine() should be called extra once to clear newline characters and avoid input skipping problems; 4. To prevent resource leakage, scanner.close() should be called after use; 5. For scenarios with high performance requirements, BufferedReader can be used to read input with InputStreamReader, but it needs to be manually

Aug 17, 2025 pm 12:17 PM

java user input

How to connect to a database in Java?

To connect to a database in Java, you need to use JDBC and follow the steps: first add the JDBC driver of the corresponding database, such as introducing the MySQL driver through Maven; modern JDBC versions can automatically load the driver without explicitly calling Class.forName; then pass the database URL, username and password to establish a connection through the DriverManager.getConnection() method; then use the Connection object to create a Statement and execute SQL query; finally be sure to close the resources, and it is recommended to use the try-with-resources statement to automatically manage resources; at the same time, you should pay attention to the running status of the database service and correctly configure the driver.

Aug 17, 2025 pm 12:13 PM

java database

Implementation tutorial on finding prime numbers in specified ranges and returning arrays in Java

This tutorial details how to efficiently find all prime numbers in a specified range in Java and collect these prime numbers into an integer array to return. We will explore the optimization of prime judgment methods, strategies for dynamic data collection (using ArrayList), and how to use the Java 8 Stream API to convert lists into arrays, and provide complete code examples and usage notes.

Aug 17, 2025 pm 12:12 PM

Tutorial on the generation of random upper case letter combinations in Java

This tutorial details how to use the Math.random() method in Java to generate a specified number of random case Latin combinations. The article will deeply parse the principle of character generation, including how to obtain uppercase and lowercase letters through ASCII code and random number mapping, and provide clear sample code and key considerations to help developers efficiently implement the random generation function of letter combinations.

Aug 17, 2025 pm 12:09 PM

The reason and solution for LiveData not passing events in callbacks

This article aims to solve the problem that observers cannot receive events when LiveData updates data in a callback function. By analyzing the difference between setValue() and postValue(), the reason why you need to use the postValue() method when updating LiveData in non-main threads is explained, and corresponding code examples and precautions are provided to help developers avoid similar errors.

Aug 17, 2025 pm 12:06 PM

Exploring Common Java Design Patterns with Examples

The Java design pattern is a reusable solution to common software design problems. 1. The Singleton mode ensures that there is only one instance of a class, which is suitable for database connection pooling or configuration management; 2. The Factory mode decouples object creation, and objects such as payment methods are generated through factory classes; 3. The Observer mode automatically notifies dependent objects, suitable for event-driven systems such as weather updates; 4. The dynamic switching algorithm of Strategy mode such as sorting strategies improves code flexibility. These patterns improve code maintainability and scalability but should avoid overuse.

Aug 17, 2025 am 11:54 AM

java Design Patterns