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How to compare Strings in Java

Use .equals() to compare string content, because == only compare object references rather than actual characters; 2. Use .equalsIgnoreCase() when comparing ignoring case; 3. Use .compareTo() when sorting alphabetically, and .compareToIgnoreCase() when ignoring case; 4. Avoid calling strings that may be null. Equals() should be used to use "literal".equals(variable) or Objects.equals(str1,str2) to safely handle null values; in short, always pay attention to content comparison rather than reference,

Aug 12, 2025 am 10:00 AM

java String comparison

Solve the problem that the database is not selected after the JDBC connection MySQL is automatically reconnected

This article discusses the root cause of the "No database selected" error when JDBC connects to MySQL because the autoReconnect property and the connection URL do not specify the database name, resulting in a long-term operation. The working principle of the automatic reconnect mechanism is analyzed in detail, and two solutions are provided: it is recommended to always include the database name in the connection URL, and to utilize the createDatabaseIfNotExist property if needed. It aims to help developers build more stable and reliable database connections.

Aug 12, 2025 am 09:57 AM

Deep understanding of the compilation types in jstat -printcompilation output

This article explores the output of the jstat -printcompilation command, especially the meaning of the Type column. This column indicates the type of JIT compilation, including regular compilation, on-stack replacement, and local method compilation. However, it should be noted that in standard JDK releases, the Type column is usually only displayed as 1 (regular compilation) due to the limitations of specific debug options, and other types are only visible in specially configured debug JVMs. Understanding this is essential for an accurate interpretation of JIT compilation activities.

Aug 12, 2025 am 09:39 AM

How to split a String in Java

Usesplit(regex)todivideastringintosubstringsbasedonadelimiter,returningaString[]array.2.Forwhitespace,use"\s "tohandlespaces,tabs,orlinebreakseffectively.3.Escapespecialregexcharacterslike.or|usingdoublebackslashes(e.g.,"\."or&quo

Aug 12, 2025 am 09:38 AM

java String splitting

Find the parent node of a specified node in a general tree: an implementation based on breadth-first search

This article details how to find the parent node of a specified node in a general tree data structure. We will adopt a Broadness-first search (BFS) strategy to check whether the child nodes of each node are the target nodes by traversing each layer of the tree. The tutorial will provide Java sample code to demonstrate how to use queues to implement this process, and discuss related precautions to help readers master the traversal and search techniques of general tree.

Aug 12, 2025 am 09:30 AM

Java JAR application output management: console display and log redirection policy

The output of System.out.println is usually invisible when a Java application is packaged into a JAR file and run with a double-click. This article will explore the reasons for this phenomenon in depth and provide two core solutions: one is to realize background logging by redirecting standard output streams and error streams to files; the other is to execute JAR files through command lines or scripts to ensure real-time visibility of console output. Mastering these methods can effectively manage the debugging information and running status of JAR applications.

Aug 12, 2025 am 09:15 AM

What is the final keyword in Java?

ThefinalkeywordinJavapreventschangestovariables,methods,orclasses.Afinalvariablecannotbereassignedafterinitialization,thoughthestateofamutableobjectitreferencescanstillbemodified.Afinalmethodcannotbeoverriddeninasubclass,ensuringconsistentbehavior.Af

Aug 12, 2025 am 08:59 AM

java final

Data loss in Java methods: Understanding parameter passing and data persistence

This article explores the common problems of data loss after Java method calls, especially when the method reassigns incoming reference type parameters. We will explain Java's parameter passing mechanism and provide two effective solutions: passing data through method return value, and directly modifying the content of the incoming reference type object. Help developers avoid such problems through specific code examples and precautions, ensuring that data is correctly passed and persisted between methods.

Aug 12, 2025 am 08:33 AM

Guide to Socket Exception Handling and Data Flow Selection in Java Network Programming

This article discusses the common Socket exceptions in Java network programming, especially the connection reset and stream corruption that may be encountered when using ObjectInputStream/OutputStream. The article analyzes the limitations of ObjectStream in network communication, emphasizes the importance of preset "exception path", and proposes more robust data exchange solutions such as BufferedReader/BufferedWriter, JSON, XML or Protobuf, aiming to help developers build stable and reliable network applications.

Aug 12, 2025 am 08:30 AM

Tutorial for regression algorithms that generate n numbers to make their sums of 100

This tutorial aims to provide an algorithm that takes the total number of numbers and the first number as input and generates a sequence of numbers with the sum of the sequence of 100. By subtracting the first number from the sum and adjusting the count accordingly, the algorithm can generate a list of numbers with regression characteristics so that the sum reaches the target value. The article will introduce the implementation of the algorithm in detail and provide Java code examples.

Aug 12, 2025 am 08:21 AM

What are comments in Java?

CommentsinJavaareignoredbythecompilerandusedforexplanation,notes,ordisablingcode.Therearethreetypes:1)Single-linecommentsstartwith//andlastuntiltheendoftheline;2)Multi-linecommentsbeginwith/andendwith/andcanspanmultiplelines;3)Documentationcommentsst

Aug 12, 2025 am 08:20 AM

java Comment

How to use PreparedStatement to prevent SQL injection in Java

Use the PreparedStatement placeholder (?) instead of user input to avoid splicing SQL strings directly; 2. Use setString, setInt and other corresponding methods to safely set parameter values; 3. It is not allowed to use placeholders to pass in table names or column names, and the dynamic structure needs to be verified through whitelists; 4. Use try-with-resources to automatically close PreparedStatement and ResultSet resources; 5. Avoid using user input to dynamically build SQL fragments, and conditional query should be implemented through parameterized logic; correctly using PreparedStatement can effectively prevent SQL injection and improve application security and maintainability.

Aug 12, 2025 am 07:56 AM

What is a method reference Javain Java?

Method reference is the abbreviation syntax for calling methods in Java, which is used to point to a method more concisely without executing it; 1. There are four types of method references: static method references (such as Integer::parseInt), instance method references for specific objects (such as System.out::println), instance method references for any object (such as String::length), and constructor references (such as ArrayList::new); 2. They are often used in functional interfaces and Stream operations, replacing lambda expressions that only call a single method; 3. Using method references can improve code readability and simplicity, for example, using list.forEach(System.ou

Aug 12, 2025 am 07:23 AM

Java method data loss: Understanding the mechanism of parameter passing and return value

This article deeply analyzes common problems of data loss in Java methods, especially when dealing with reference types such as arrays. We will explore how Java's by-value mechanism causes the reassignment of referenced parameters inside the method to not affect external variables. The article provides solutions to effectively pass data through method return values, supplemented by detailed code examples, aiming to help developers avoid such errors and ensure that data is properly passed and persisted in the program flow.

Aug 12, 2025 am 07:12 AM