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What are streams in Java IO?

Java I/O streams are divided into byte streams and character streams, which are used to process binary data and text data respectively. 1. Byte streams read and write data in units of bytes. Common classes include InputStream and OutputStream; 2. Character streams operate text in units of characters. The default is platform encoding. Common classes are Reader and Writer; 3. Common stream classes include FileInputStream/FileOutputStream, BufferedInputStream/BufferedOutputStream, FileReader/FileWriter, BufferedReader/Buffered

Jun 25, 2025 pm 05:01 PM

streams java io

What is `fail-fast` behavior?

Fail-fastbehavior is a design principle that stops and reports immediately when errors are found, used to quickly expose problems to avoid subsequent risks. 1. In programming languages ??and libraries, such as Java's ConcurrentModificationException, Python iterative modification errors, and unit test failures, which helps quickly locate errors. 2. In API design, prevent error spread by verifying parameters as early as possible, such as function limiting the percentage range throws exceptions in advance. 3. Practices such as CI/CD construction failure, front-end form pre-checking, priority writing of unit tests, etc. in the development process can also speed up problem feedback. Although it is not suitable for all scenarios, if you need fault-tolerant online services,

Jun 25, 2025 pm 04:45 PM

Behavior

What is garbage collection root?

The GC root is the starting point for the garbage collector to determine the surviving object, and it traces whether the object is reachable through the reference chain to determine whether it is recycled. The main types include: 1. Local variables; 2. Active threads; 3. Static fields; 4. JNI references. During operation, GC starts from these root nodes to mark all reachable objects, and those that are not marked are collected as garbage. Understanding GC roots can help troubleshoot memory leaks. Common reasons such as unregistered listeners, uncleaned thread local variables, or continuously growing static collections can be discovered and resolved by analyzing the root path.

Jun 25, 2025 pm 04:37 PM

Garbage collection Root object

What is the JDK?

JDK (JavaDevelopmentKit) is a software development environment for developing Java applications and applets. It contains tools and libraries required to compile, debug and run Java programs. Its core components include Java compiler (javac), Java runtime environment (JRE), Java interpreter (java), debugger (jdb), document generation tools (javadoc) and packaging tools (such as jar and jmod). Developers need JDK to write, compile Java code and develop with the help of IDE; without JDK, Java applications cannot be built or modified. You can enter javac-version and java-version in the terminal

Jun 25, 2025 pm 04:05 PM

java jdk

What is the difference between composition and aggregation?

The difference between Composition and aggregation is the tightness of association between objects. 1. Composition is a strong "ownership" relationship. The child object cannot exist independently of the parent object, such as car and engine, life cycle binding, and is represented by a solid diamond in UML; 2. Aggregation is a weak "ownership" relationship, and the child object can exist independently, such as department and teacher, life cycle not bound, and is represented by a hollow diamond in UML; 3. When selecting a combination, if the part leaves the whole and is meaningless or needs to control its life cycle, such as windows and borders; 4. When selecting aggregation, if the part can exist independently and needs to be shared flexibly, such as school and students. The key to judging is whether the sub-object can exist independently.

Jun 25, 2025 pm 03:57 PM

combination polymerization

Difference between Iterator and ListIterator?

The main differences between Iterator and ListIterator are reflected in four aspects: 1. Different traversal directions: Iterator can only traverse one-way, while ListIterator supports two-way traversal; 2. Different operational capabilities: Iterator only supports deleting elements, while ListIterator supports adding, modifying and deleting elements; 3. Different scope of use: Iterator can be used for all Collection subclasses such as Set, List and Queue, while ListIterator is only applicable to List; 4. Different acquisition methods: Iterator is obtained through collection.iterator(), while ListI

Jun 25, 2025 pm 02:57 PM

What is `ExecutorService`?

ExecutorServiceisaJavainterfacethatsimplifiesmanagingandrunningtasksconcurrently.Insteadofmanuallycreatingandhandlingthreads,youcanuseittosubmittasks(likeRunnableorCallable)andlettheservicehandletheexecutiondetailsfor

Jun 25, 2025 pm 02:53 PM

How to use reflection?

Reflection is used to dynamically operate classes and objects at runtime, and is commonly used in general tool development. Its core steps include obtaining class information, viewing structures, creating instances, calling methods, and accessing private members; when using it, you need to pay attention to performance, security, maintainability and version compatibility issues.

Jun 25, 2025 pm 02:09 PM

What are wildcards in generics?

WildcardsingenericsprovideflexibilitybyallowingunknowntypesinJava.1.Upper-boundedwildcards()areusedwhenthetypeisirrelevant,supportingallparameterizedtypes.Thesewildcardsensurecompile-timetypesafetywhileenablinggenericcodereuse,particularlyusefulincol

Jun 25, 2025 pm 02:05 PM

How to use enums?

Enumeration is suitable for scenarios such as finite states, control branches, classification options, etc. It is recommended to use PascalCase for naming, and the values ??are in full or first letter capital to avoid redundant prefixes. Different languages ??such as Python, TypeScript, and Java support for enumerations differently and require unified team specifications. When using it, you should avoid confounding irrelevant values, fix common values, consider data mapping, and separate common enumerations from sharing.

Jun 25, 2025 pm 01:49 PM

What is externalization?

Externalization is a psychological technique commonly used in narrative therapy, and its core is to help people separate problems from themselves. 1) By naming or giving a question its independent identity, such as "anxiety" or "Mr. Procrastination", individuals learn to look at the problem in a more objective way; 2) then describe how the problem affects life, when it occurs and the behaviors and emotions it brings; 3) ultimately challenge the impact of the problem and regain control. This approach reduces self-blame and shame, stimulates curiosity, prompts people to reflect on the root causes of the problem and take positive actions to promote change. It is suitable for anxiety, depression, addiction and other problems, and can also be used to deal with thinking patterns such as self-doubt or perfectionism.

Jun 25, 2025 pm 01:05 PM

What is an instance initializer block?

Instance initialization blocks are used in Java to run initialization logic when creating objects, which are executed before the constructor. It is suitable for scenarios where multiple constructors share initialization code, complex field initialization, or anonymous class initialization scenarios. Unlike static initialization blocks, it is executed every time it is instantiated, while static initialization blocks only run once when the class is loaded.

Jun 25, 2025 pm 12:21 PM

What is an Error in Java?

Errors in Java are uncontrollable runtime issues and should not be handled by programs. 1. Error indicates serious problems at the JVM or environment level, such as OutOfMemoryError, StackOverflowError, etc.; 2. Common types include VirtualMachineError, LinkageError, and ThreadDeath; 3. Errors should not be caught because they are usually unable to be restored; 4. Errors are different from exceptions, the former should not be caught, and the latter (Exception) can be handled; 5. When an error is encountered, you should analyze the stack trace, check resource limitations, review library compatibility, and monitor logs.

Jun 25, 2025 pm 12:06 PM

How to create custom annotations?

Custom annotations can enhance the code function through metadata. Java uses @interface definition and combines reflection reading. Examples include @Todo annotation annotation to annotate to do; Python uses decorators to simulate annotation behavior; when using it, it should reasonably design the scope of action, avoid abuse, strengthen document descriptions, and cooperate with tool chains to improve efficiency.

Jun 25, 2025 am 11:29 AM