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What is the `throws` keyword?

ThethrowskeywordinJavaisusedtodeclarecheckedexceptionsthatamethodmaythrow,passingtheresponsibilityofhandlingthemtothecaller.1.Itallowsamethodtospecifywhichexceptionsitdoesnothandle,requiringthecallertoeithercatchthemorpropagatethemfurther.2.Itisusede

Jun 26, 2025 am 01:14 AM

What is the diamond operator ``?

The diamond operator is used to simplify the instantiation of generic classes in Java. 1. Improve code readability and avoid repeated declaration of types; 2. The compiler can automatically infer types, which is suitable for collection creation, custom generic classes and method chain calls; 3. Manually specify the type when complex overloading or return types are fuzzy; 4. It is recommended to define a complete generic type and use tools to check type inference.

Jun 26, 2025 am 01:11 AM

java Diamond operator

How to create a custom exception?

Custom exceptions are implemented in Python by inheriting the Exception class or its subclasses, which are used to improve code readability and targeted error handling. When built-in exceptions cannot meet specific business needs, for example, you need to distinguish between multiple user input error scenarios, you can create different exception types such as InvalidEmailError and PasswordTooShortError. The creation method is simple. You only need to define a new class. You can also add initialization parameters such as message and error_code to provide more information to assist in debugging. Suitable scenarios for using custom exceptions include modular projects, business rule verification, and third-party library development, such as the data parsing module that defines ParseError

Jun 26, 2025 am 01:11 AM

Difference between Statement and PreparedStatement?

The core difference between Statement and PreparedStatement is security, performance, and maintainability. 1. In terms of security, PreparedStatement uses parameterized queries to prevent SQL injection, while Statement directly splicing strings is vulnerable to attack; 2. In terms of performance, PreparedStatement precompiled and caches SQL, making repeat execution more efficient; 3. In terms of maintainability, PreparedStatement has a clearer parametric writing structure, which is easy to maintain; 4. It is recommended that PreparedStatement be used first in scenarios involving user input or frequent execution, and Statement can be used in simple scripts.

Jun 26, 2025 am 01:09 AM

Difference between synchronized method and block?

Synchronizedblocksaregenerallybetterwhenyouneedfine-grainedcontrol,flexibilityinchoosinglockobjects,andimprovedperformancebylockingonlycriticalsections.1.Synchronizedmethodslocktheentiremethodandusetheobjectorclassasthelock,leadingtobroaderlockingtha

Jun 26, 2025 am 01:07 AM

How to access array elements?

The key to accessing array elements is to master the index usage and language syntax habits. 1. The index usually starts from 0 and obtains data through position number, such as fruits[0], which represents the first element; 2. Negative indexes can represent the end element, such as Python fruits[-1]; 3. Accessing the out-of-bounds index may report an error or return an uncertain value, so you need to pay attention to boundary judgment; 4. It can traverse the array by batch processing elements, such as for loops, foreach and other methods, such as JavaScript for loops or forEach functions; 5. Multi-dimensional arrays need to use multiple indexes to access nested elements, such as Python matrix0, which represents the second element on the first line. There may be differences in syntax of different languages, and the document should be used as

Jun 26, 2025 am 01:06 AM

What is the ServiceLoader API?

ServiceLoaderinJavadynamicallyloadsserviceimplementationsatruntimebyscanningMETA-INF/servicesfiles.1.Itdecouplescodefromspecificimplementations.2.ItscansJARsforconfigurationfileslistingimplementationclasses.3.Itusesthecontextclassloadertoinstantiatet

Jun 26, 2025 am 01:06 AM

What is `CompletableFuture`?

CompletableFutureinJavasimplifiesasynchronousprogrammingbyenablingnon-blockingcodewithgreaterflexibilitythanthetraditionalFutureinterface.1.Itallowsmanualcompletionoftasksusingcomplete(),2.supportsasyncexecutionviarunAsync()orsupplyAsync(),3.enablesc

Jun 26, 2025 am 01:05 AM

What are default methods in interfaces?

The default method allows methods with implementations to be defined in Java interfaces, and default keyword is modified by default, solving the problem of destroying existing implementations when interface extensions. For example, if the stream() method is added to the Collection interface, if it is abstract, all subclass implementations are required, and the default method allows it to be automatically inherited. When multiple interfaces contain the same default method, the specified call needs to be manually rewrite, such as using A.super.sayHello() to explicitly select implementation. Its main application scenarios include collection framework enhancement, providing optional behavior, and simplifying template method patterns, but abuse should be avoided to prevent interface bloat.

Jun 26, 2025 am 01:03 AM

Why use the `Serializable` interface?

ImplementingtheSerializableinterfaceinJavaallowsaclasstobeconvertedintoabytestreamforstorageortransmission.Asamarkerinterfacewithnomethods,itsignalsthattheclassisreadyforserialization,enablingmechanismslikeObjectOutputStreamtoprocessit.Failingtoimple

Jun 26, 2025 am 01:02 AM

java

How to connect to a database using JDBC?

The key to using JDBC to connect to databases is to correctly configure the driver and URL. 1. Prepare the JDBC driver: Download the corresponding driver package according to the database type, add dependencies through pom.xml for the Maven project, and manually add .jar files to buildpath for ordinary projects; for example, MySQL uses mysql-connector-java. 2. Use the correct URL format: such as jdbc:mysql://localhost:3306/mydatabase?useSSL=false&serverTimezone=UTC, pay attention to the host address, port and parameter settings. 3. Load the driver and establish a connection: it can be passed through Cl

Jun 26, 2025 am 01:01 AM

What is the Singleton pattern?

Singleton pattern is used to ensure that a class has only one instance and provides a global access point. 1. Prevent external instance creation through private constructors. 2. Create a static private instance inside the class. 3. Provide a public static method to obtain the instance. Implementation needs to pay attention to thread safety, such as using double check locking or static internal classes. Advantages include resource saving and unified management, while disadvantages are high coupling, hiding dependence, and complex multi-threading processing.

Jun 26, 2025 am 01:01 AM

Design Patterns

What is TestNG?

TestNG is a Java-based test framework, mainly used for automated testing. It is more powerful and flexible than JUnit, and is suitable for various scenarios such as unit testing, integration testing, etc. Its core features include: 1. Supports multiple test types; 2. Powerful annotation system; 3. Supports concurrent execution; 4. Parameterized testing; 5. Test grouping and dependency management; 6. Produced report generation function. Compared with JUnit, TestNG has a more flexible annotation mechanism, naturally supports dependency testing, and is more suitable for automated testing projects. To start using TestNG, you can follow these steps: 1. Add Maven dependencies; 2. Write test classes with annotations; 3. Run tests through the IDE or command line; 4. View the generated HT

Jun 26, 2025 am 12:59 AM

What is the equals method contract?

In Java, five rules must be followed when overriding the equals() method: reflexivity, symmetry, transitiveness, consistency and non-emptiness. 1. Reflexivity requires that the object compares with itself returns true; 2. Symmetry ensures that the results of x.equals(y) and y.equals(x) are consistent; 3. Transmission requirements: If x.equals(y) and y.equals(z) are true, then x.equals(z) should also be true; 4. Consistency ensures that the result of the same object calls equals() multiple times unchanged; 5. Non-empty stipulates that the object compares with null should return false. In addition, hashCode() must be overwritten at the same time when overwriting equals() to ensure that the phase

Jun 26, 2025 am 12:59 AM