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Connecting Java to Specific Databases like MySQL

Java applications to connect to MySQL usually use JDBC. The specific steps are as follows: 1. Add MySQLJDBC driver dependencies (such as Maven configuration) or manually add JAR; 2. Make sure that the MySQL service is running and ready for connection information (host, port, database name, user name and password); 3. Use DriverManager.getConnection() to establish a connection, and pay attention to the JDBCURL format and automatic driver loading characteristics; 4. Perform query and operations through Statement or PreparedStatement, and use PreparedStatement to prevent SQL injection; 5. Close ResultSet correctly,

Jul 04, 2025 am 02:09 AM

mysql java

What are the different types of classloaders in Java?

Java class loaders are divided into four categories. BootstrapClassLoader is implemented by C/C and is responsible for loading the JVM core class library such as rt.jar; ExtensionClassLoader loads the extended class library, with the default path being java.ext.dirs; ApplicationClassLoader is responsible for loading classes under the user class path, with the default path being controlled by java.class.path; Custom ClassLoader inherits the ClassLoader class and is used to implement specific loading logic, such as hot deployment, encrypted class loading, etc., and usually follows the parent delegation model to ensure security.

Jul 04, 2025 am 01:50 AM

java class loader

Correctly Overriding equals() and hashCode() in Java

The way to properly rewrite equals() and hashCode() in Java is the key to ensuring that objects work properly in collection classes. If you only rewrite equals() and not hashCode(), objects with the same content will be mistaken for different keys, because the hash set depends on hashCode() to determine the storage location. 1. When rewriting equals(), you should first check whether it is the same object, whether it is null or type mismatch, and then compare fields one by one; 2. Rewriting hashCode() must be consistent with equals(), and commonly used Objects.hash() to generate comprehensive hash values; 3. Use the IDE automatic generation method to avoid errors and improve readability; 4. Use L

Jul 04, 2025 am 01:34 AM

java equals()

How to handle NullPointerException in Java?

When encountering null pointer exceptions, you should avoid them from the source rather than relying solely on try-catch. 1. Understand that it comes from the attributes or methods that access null objects, such as the method returns null or the object is not initialized. 2. Actively check null before use. Java 8 can use Optional to force null. 3. Use Objects.requireNonNull() and Objects.equals() to assist in judgment and comparison. 4. Develop defensive programming habits, avoid returning null, and use empty sets or annotations to prompt potential problems.

Jul 04, 2025 am 01:33 AM

java

What are different garbage collectors?

There are 5 main types of garbage collectors in Java, each suitable for different scenarios. 1. SerialGC single-threaded operation, suitable for small applications and single-core systems; 2. ParallelGC multi-threaded processing, focusing on throughput, suitable for batch tasks; 3. CMS concurrent mark clearance, reducing latency but increasing resource consumption, suitable for response time-sensitive applications; 4. G1 partition recycling, balancing throughput and latency, suitable for large-scale memory; 5. ZGC and Shenandoah support ultra-low latency and TB memory, suitable for real-time high-load services. When choosing, it must be determined based on application scale, performance requirements and hardware conditions.

Jul 04, 2025 am 01:26 AM

java Garbage collection

Implementing Dependency Injection in Java Applications

Dependency injection (DI) achieves decoupling through the dependencies of external control objects, improving code testability, maintainability and flexibility. 1. DI is a design pattern, and the core is to create it by external incoming dependencies rather than objects themselves; 2. Common injection methods include constructor injection (most commonly used), Setter injection (suitable for optional dependencies), and field injection (not recommended); 3. DI can be implemented manually, such as passing dependencies through constructors; 4. Using Spring framework can simplify dependency management, and automatically handle dependencies through @Component and @Autowired annotations; 5. Pay attention to avoiding complex constructors and bean conflicts, not all classes need framework management. Mastering these key points can make it more efficient in Java

Jul 04, 2025 am 01:14 AM

java dependency injection

What are Records in Java?

JavaRecords is a feature introduced by Java16 to simplify the definition of immutable data classes. It automatically generates common methods such as construction methods, getter methods, toString(), equals() and hashCode() through a line of code to reduce redundant code and improve development efficiency; its advantages include simplicity, immutability, thread safety and ease of debugging; suitable for packaging when returning multiple values ??in DTO, JSON serialization, configuration classes and functional programming; but it is not suitable for scenarios where object state needs to be frequently modified or other classes need to be inherited; in addition, record can implement interfaces and support the addition of static factory methods to enhance readability, such as using Person.of("T

Jul 04, 2025 am 12:54 AM

Managing Dependencies with Java Maven or Gradle

In Java projects, the following key points must be mastered: 1. Understand dependency transfer and scope, and reasonably set the scope of compile, runtime, test, etc. to avoid redundant dependencies; 2. Unify the version number, centrally manage it through Maven's properties or Gradle's versions.gradle, and use BOM to unify the dependency set version; 3. Use tools such as mvndopendency:tree or gradled dependencies to troubleshoot conflicts, and resolve conflicts by explicitly specifying the version, excluding dependencies or force strategies; 4. In multi-module projects, Maven uses the parent POM and G

Jul 04, 2025 am 12:43 AM

Immutability of String Objects in Java Explained

StringsinJavaareimmutableforperformance,security,andmemoryefficiency.1.ImmutabilityallowstheJVMtooptimizestringpooling,reducingmemoryusagebyreusingidenticalstringobjects.2.Securityisenhancedbecausemutablestringscouldbealteredunexpectedlywhenpassedtom

Jul 04, 2025 am 12:42 AM

java string

Introduction to Java Native Interface (JNI) Use Cases

Common usage scenarios for JNI include improving the execution efficiency of performance-sensitive parts, accessing operating system or hardware-specific features, reusing existing local library resources, and enhancing security and anti-reverse protection. 1. For high-performance tasks such as image processing, encryption and decryption, C/C can be used to implement key logic through JNI to improve efficiency, but attention should be paid to cross-language call overhead; 2. When accessing device drivers, sensor data or system APIs is required, it can be implemented with the help of the JNI call platform related local libraries, and compatibility issues should be considered; 3. In order to reuse existing C/C code assets, it can be encapsulated through JNI for Java application calls to reduce duplicate development, but a reasonable interface should be designed; 4. Placing the key logic at the native layer can increase the reverse difficulty

Jul 04, 2025 am 12:26 AM

jni

What is `BufferedWriter`?

BufferedWriter is a class in Java for efficient writing character streams. It reduces the number of I/O operations through a buffering mechanism and improves performance. 1. When creating, you need to pass in FileWriter or other Writer subclasses; 2. Common methods include write() to write strings, newLine() to break lines, flush() to force refresh, close() to close() to close the stream; 3. Use try-with-resources to ensure automatic closing of the stream; 4. Appropriately refresh, handle exceptions, and prioritize large amounts of data writing.

Jul 03, 2025 am 02:24 AM

What is type erasure?

TypingasureexistsinlanguagoezeslikejavaandwifttomaintainbackwardcompatibilityandruntimeefficiCybyremoving generative type formation runningime.1.Tensurescompile-TimetypesafetywoodburdeningTeRuntime-TimeTata.2.injava-TimeTata.2.injavaTueCileCilePedata.2.

Jul 03, 2025 am 02:23 AM

How to write to a file in Java?

Writing files in Java can be implemented in many ways, mainly including the following methods: 1. Use FileWriter and BufferedWriter to create a BufferedWriter object and call the write method to write content, supporting append mode and automatic resource management; 2. Use the Files class (recommended), and write string or list content at one time through the Files.write method, supporting overwrite and append mode, and specifying character sets; in addition, you need to pay attention to common problems such as paths, encodings, permissions and newlines to ensure that the file is written correctly.

Jul 03, 2025 am 02:22 AM

Difference between `volatile` and `synchronized`?

volatileensuresvisibilityofvariablechangesacrossthreadsbutlacksatomicity,whilesynchronizedprovidesbothvisibilityandatomicity.Usevolatileforsingleoperationswithoutcompoundactions,likesettingflags.Usesynchronizedformulti-stepoperationsrequiringmutualex

Jul 03, 2025 am 02:20 AM