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Checked vs unchecked exceptions in Java explained.

Checked exceptions are exceptions that must be processed during compilation, such as IOException and SQLException, which need to be declared by try-catch or throws, otherwise an error will be reported in the compilation; non-checked exceptions are runtime exceptions, such as NullPointerException and ArrayIndexOutOfBoundsException, which the compiler does not force processing. 1. Checkedexception is suitable for errors that the caller must handle, such as the IO operation fails, suitable for scenarios where recovery, retry or explicit processing is required; 2.unchec

Jul 05, 2025 am 12:47 AM

Java Logging frameworks comparison (e.g., Log4j2, SLF4J, Logback).

SLF4J is a log interface, and Logback and Log4j2 are implementation frameworks; 1. SLF4J is a unified interface, providing decoupling capabilities, which facilitates the later replacement of the underlying log system; 2. Logback is developed by the SLF4J author, fast startup, good performance, natural integration, flexible configuration, suitable for SpringBoot projects; 3. Log4j2 has powerful functions, outstanding asynchronous logging performance, suitable for high-concurrency scenarios, but complex configuration and attention to security vulnerabilities; Selection suggestions: SpringBoot uses Logback by default, Log4j2 is selected for high-performance requirements, and SLF4J is required for code decoupling. Old projects can be considered for upgrading or migration.

Jul 05, 2025 am 12:37 AM

Log Framework

Explain Dependency Injection in Java frameworks like Spring.

Dependency injection (DI) is a design pattern that enables loose coupling of code by externally managing dependencies of objects. Its core lies in injecting object dependencies from the outside rather than internal creation, thereby improving flexibility and maintainability. For example, in the UserService, pass into the UserRepository instance through the constructor, that is, the constructor injection. Spring framework supports multiple injection methods through IoC containers: 1. Constructor injection, suitable for forced dependencies; 2. Setter injection, suitable for optional dependencies; 3. Field injection (@Autowired), using annotations directly in fields. Advantages of DI include: decoupling, enhanced testability, flexible configuration, and easy maintenance. In practical applications, you need to pay attention to: avoid

Jul 05, 2025 am 12:29 AM

What is the difference between == and .equals() in Java?

InJava,==comparesobjectreferenceswhile.equals()checksforvalueequality.1.==verifiesiftwovariablespointtothesamememoryinstance,returningfalsefordistinctobjectswithsimilarcontent.2..equals()evaluateslogicalequalitybasedonvalues,butreliesonpropermethodov

Jul 04, 2025 am 02:56 AM

Explain the concept of Java Modules (JPMS).

JavaModulesareafeatureintroducedinJava9toimprovecodeorganization,maintainability,andsecurity.1.Theyallowdeveloperstogrouprelatedpackagesintomoduleswithexplicitdependenciesandexports.2.Eachmoduleincludesamodule-info.javafilethatdeclaresitsname,require

Jul 04, 2025 am 02:56 AM

JPMS

Understanding Type Erasure in Java Generics

Java generics provide type checking at compile time, but type erasing is performed at runtime. 1. Type erasure means that both List and List are both List types at runtime, resulting in the inability to use generic overload methods; 2. Limitations include not being able to create instances using newT(), not being able to make instanceof judgments, and not being able to declare generic arrays; 3. Solutions include preserving generic information through subclasses, using reflection to obtain generic signatures, or manually passing Class parameters. These mechanisms help understand the limitations and how Java generics are handled.

Jul 04, 2025 am 02:56 AM

java generics Type erasure

How to use the `Optional` class in Java?

Java's Optional class avoids null pointer exceptions by explicitly indicating missing values. 1. Use Optional.of() to create a non-empty object, Optional.ofNullable() handles objects that may be empty, Optional.empty() represents a null value; 2. Check whether there is a value through isPresent(), get() gets the value but be careful; 3. Use orElse() and orElseGet() to provide the default value, and orElseThrow() throws an exception when there is no value; 4. Implement chain calls through map(), flatMap(), and filter() to simplify logic. Optional is suitable for rebate

Jul 04, 2025 am 02:54 AM

Exploring Different Synchronization Mechanisms in Java

Javaprovidesmultiplesynchronizationtoolsforthreadsafety.1.synchronizedblocksensuremutualexclusionbylockingmethodsorspecificcodesections.2.ReentrantLockoffersadvancedcontrol,includingtryLockandfairnesspolicies.3.Conditionvariablesallowthreadstowaitfor

Jul 04, 2025 am 02:53 AM

java Synchronization mechanism

How to use the Builder Pattern in Java.

The Builder pattern is a creative design pattern used to build complex objects in steps. It separates the object's construction process from its representation, making the code clearer and easier to expand. 1. Suitable for scenarios where the class has multiple optional fields, too many constructor parameters, and requires flexible control of the construction process; 2. It can be manually implemented by defining internal static classes, using chain calls to set parameters and calling the build() method to generate objects; 3. Lombok provides @Builder annotation to automatically generate Builder code to improve development efficiency; 4. It is recommended to use it when there are more than 4 parameters, default values ??or verification logic, and hope to improve readability, but simple objects do not need to be used.

Jul 04, 2025 am 02:51 AM

Differences Between Callable and Runnable in Java

There are three main differences between Callable and Runnable in Java. First, the callable method can return the result, suitable for tasks that need to return values, such as Callable; while the run() method of Runnable has no return value, suitable for tasks that do not need to return, such as logging. Second, Callable allows to throw checked exceptions to facilitate error transmission; while Runnable must handle exceptions internally. Third, Runnable can be directly passed to Thread or ExecutorService, while Callable can only be submitted to ExecutorService and returns the Future object to

Jul 04, 2025 am 02:50 AM

java Multithreading

Exploring Java Reflection API Capabilities

The Java reflection API is a tool for dynamically obtaining class information and operating class members when a program runs. The core answer is: it allows the runtime to load classes, access private members, create instances and call methods. 1. The class can be loaded dynamically through Class.forName(); 2. Use getDeclaredConstructor().newInstance() or setAccessible(true); 3. Call methods through getMethod() and invoke(); 4. Support obtaining structural information such as methods, fields, constructors of the class; 5. You can access private members but use them with caution; 6. Pay attention to performance overhead, security restrictions, and encapsulation corruption when using them

Jul 04, 2025 am 02:44 AM

java

How to use enhanced for loop?

Enhanced for loops are suitable for scenarios where no indexing and read-only operations are required. 1. Access elements one by one when iterating through an array or collection; 2. Check whether the object meets the conditions; 3. Accumulate the sum of numerical values; its syntax is for (type variable: array or collection), which can be applied to data structures such as array, ArrayList, HashSet and HashMap; but the content of the element cannot be modified, the index cannot be obtained, and it is not suitable for multi-dimensional array operations. Common errors include trying to delete elements or modify array values. At this time, traditional for loops should be used.

Jul 04, 2025 am 02:40 AM

When and How to Use Java Optional Correctly

Optional should only be used for return values ??and is not recommended as parameters or fields. 1. Using Optional in the return value can make it clear that the result may be empty, avoid null pointers and improve readability; 2. Using Optional in parameters and fields will increase complexity and may lead to serialization problems; 3. Over-necking of Optional will make the logic more complicated, and you should use if to judge first; 4. It is recommended to use of Nullable to create Optional to deal with uncertainty about whether there is a value.

Jul 04, 2025 am 02:40 AM

java optional

When and How to Use the 'assert' Keyword in Java

YoushouldusetheassertkeywordinJavatotestassumptionsduringdevelopmentanddebugging,particularlyforcatchinglogicerrorsthatindicateinternalbugs.1.Assertisusedtoperforminternalconsistencychecks,suchasvalidatingmethodreturnvaluesorprivatemethodparameters.2

Jul 04, 2025 am 02:38 AM