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What are generics in Java?

GenericsinJavaenabletype-safereusablecodebyallowingclasses,interfaces,andmethodstooperateonanydatatype.IntroducedinJava5,theypreventruntimeerrorsbycatchingtypemismatchesatcompiletime,asseenwhenusingcollectionslikeListthatdisallowaddingincompatibletyp

Jun 30, 2025 am 12:28 AM

How to use the `static` keyword?

The static keyword is used in Java to modify variables, methods, and internal classes, and is at the class level rather than the instance level. 1. StaticVariables are shared by all objects, suitable for counter or constant definitions, and it is better to define constants using publicstaticfinal; 2. StaticMethods are called directly through the class name, and cannot access non-static members, and are suitable for tool classes and factory methods; 3. StaticBlocks are executed once during class loading and are used to initialize static resources or configurations; 4. StaticNestedClasses do not rely on external class instances to improve encapsulation and performance

Jun 30, 2025 am 12:19 AM

How to compare strings in Java?

You cannot use the == operator to compare string content in Java because it compares object references rather than content. The following methods should be used: 1. Use the .equals() method to determine whether the content is the same. This is the most commonly used and recommended method. Please note that strings that are not null are placed in front of them to avoid null pointer exceptions; 2. Use the .equalsIgnoreCase() method to ignore case comparisons, which is suitable for handling user input or configuration files. 3. Use the .compareTo() method to compare string order and size, return 0 to mean equality, and negative numbers indicate the current string before the parameter string, and positive numbers are the opposite, and are suitable for sorting or alphabetical processing; 4. Avoid using == to compare

Jun 30, 2025 am 12:12 AM

How to create a thread?

To create an engagement discussion post, you must first clarify the topic, such as "Why is remote working more and more difficult to manage now?" or "I spent 3 months optimizing my early-wake habits. These 5 methods are the most effective", so that people can see the core of the content at a glance. Secondly, use numbers or steps to enhance readability, such as three steps: the first step is to identify the problem, the second step is to analyze the cause, and the third step is to provide a solution. At the same time, sentence patterns such as "I discovered a rule" and "I tried 3 methods, only this is useful" can be used to enhance the attractiveness. Furthermore, control the rhythm, tell a small dot in each tweet, keep it simple, 1 to 2 sentences, and appropriately split the complex content, interspersed with questions or summary sentences to stimulate interest. The last few should be carefully designed to avoid hasty endings, and can be used to introduce them by invitation interaction or summary.

Jun 29, 2025 am 01:32 AM

What is the `super` keyword?

The super keyword is used to call the parent class's methods or access the parent class attributes. Common uses include calling the parent class methods, initializing the parent class constructor, and handling method override and multiple inheritance. 1. When calling the parent class method, you can use super.method() in the subclass to preserve the original behavior; 2. When initializing the constructor, you need to use super() to ensure that the parent class is initialized correctly; 3. In multiple inheritance, super() calls the next parent class method in the order of method parsing, making the inheritance chain clearer and easier to maintain. Use super rationally to improve code maintainability, but excessive use can cause logical confusion.

Jun 29, 2025 am 01:31 AM

oop super keywords

What is a HashSet?

HashSet is a collection based on a hash table, with elements that are non-repeatable and highly query efficient. Its core features include: 1. Unordered, elements have no fixed order and cannot be accessed through the index; 2. Uniqueness, adding duplicate values ??will be automatically ignored; 3. Efficient query, the time complexity of insertion, deletion and search is close to O(1). Compared with List, List is ordered, allows repetition and has lower query efficiency. Common operations include add(), remove() removal, contains() judgment existence, and size() obtaining quantity. When using it, you need to pay attention to overriding the equals() and hashCode() methods for custom classes. Suitable for deduplication, quick search and collection operation scenarios.

Jun 29, 2025 am 01:30 AM

data structure hashset

What is the Java Collections Framework?

The Java Collection Framework (JCF) is a set of classes and interfaces for storing and manipulating data collections, providing a unified and efficient way to process core data. It mainly includes three core interfaces: 1.Collection interface, which derives List, Set and Queue. List is an ordered and repeatable collection. Common implementations include ArrayList and LinkedList; 2.Set is a collection of non-repeated elements, such as HashSet and TreeSet; 3.Map is used to store key-value pairs, and common implementations include HashMap and TreeMap. Implementation classes are selected according to different scenarios, such as frequent access to ArrayList, insert and delete multiple uses LinkedList, go to

Jun 29, 2025 am 01:29 AM

java collection

How to refactor code?

The core of refactoring code is continuous improvement rather than rewriting. First, it is necessary to clarify the goals, such as solving problems such as confusion in code, excessive function, and difficulty in scaling; secondly, there must be test guarantees to ensure that the changes do not destroy the original functions; then iterate in small steps, only one change is made at a time and run the test to confirm that it is correct; finally, you can use tools to improve efficiency, such as using the built-in refactoring function and static analysis tools of IDE.

Jun 29, 2025 am 01:27 AM

What are buffers in NIO?

Buffers are used in NIO to efficiently manage data input and output operations. Its core mechanisms include: 1. Use buffers to temporarily store data to improve read and write efficiency; 2. The buffer has three key attributes: capacity, location and limitation, and switches read and write modes through the flip() method; 3. Provides multiple types of buffers such as ByteBuffer, CharBuffer, etc. to adapt to different data types; 4. Direct buffers can improve performance but consume more resources; 5. Suitable for non-blocking I/O, high-performance network servers, and large file processing scenarios.

Jun 29, 2025 am 01:19 AM

What is a for loop?

Aforloopisusedtorepeatcodeaspecificnumberoftimesoriteratethroughacollection.1.Itworksbyinitializingacounter,definingacondition,andupdatingthecounteraftereachiteration.2.Commonusesincludeprocessinglists,repeatingactions,iteratingthroughstrings,andperf

Jun 29, 2025 am 01:18 AM

How to use Maven build tool?

Maven is a widely used build tool in Java projects. Its core value lies in simplifying dependency management and unified construction process. 1. Before installing Maven, make sure that JDK is installed. After downloading, configure the environment variables MAVEN_HOME and PATH, set %MAVEN_HOME%\bin by Windows users, modify the .bash_profile or .zshrc file by Mac/Linux users, and customize the local repository path through .m2/settings.xml. 2. Create a Maven project by executing mvnarchetype:generate to generate a standard structure, or create a new Maven project in the IDE to automatically complete it. 3

Jun 29, 2025 am 01:17 AM

Build tools maven

What is the stack space?

Stackspaceisafastbutlimitedmemoryareausedfortemporaryvariablesinfunctions.Itstoresparameters,localvariables,andreturnaddresses.Eachfunctioncalladdsaframetothestack,whichisremovedwhenthefunctionfinishes.Stackspacemattersbecauseitisessentialyetlimited,

Jun 29, 2025 am 01:10 AM

What is an instance variable?

An instance variable is a variable defined in a class or outside a method, and belongs to an instance of a class. 1. They are different from class variables, and each instance has an independent copy; 2. They are often declared on the top of the class or before the constructor, and are used to store the data unique to the object; 3. Allocate memory when creating the object and accessed through self.variable_name; 4. Common errors include forgetting to use self, not initializing it in __init__, and misuse of mutable objects to cause data sharing.

Jun 29, 2025 am 01:09 AM

How does a while loop work?

Awhileloopexecutescoderepeatedlyaslongasaconditionremainstrue.1.Itcheckstheconditionbeforeeachiterationandstopswhentheconditionbecomesfalse.2.Itisusefulwhenthenumberofiterationsisunknown,suchaswaitingforuserinputormonitoringstatuschanges.3.Commonpitf

Jun 29, 2025 am 01:07 AM

cycle