99久久综合精品五月天,а√天堂资源地址在线下载

Article Tags

Home

Technical Articles

Java

What is the volatile keyword? (Rephrased)

volatiletellsthecompilernottooptimizeaccessestoavariablethatmaychangeunexpectedly,ensuringmemoryreads/writesoccurasintended.1.Itpreventscachinginregistersandenforcesmemoryaccessoneveryread/write.2.Itlimitsinstructionreorderingaroundthevariable(butnot

Jun 25, 2025 am 11:09 AM

Keywords volatile

What is a deadlock?

Adeadlockoccurswhenfourconditionscoexist:mutualexclusion,holdandwait,nopreemption,andcircularwait.1.Mutualexclusionmeansatleastoneresourcecannotbeshared.2.Holdandwaitoccurswhenaprocessholdsoneresourcewhilewaitingforanother.3.Nopreemptionmeansresource

Jun 25, 2025 am 10:21 AM

How does HashMap work internally?

HashMap realizes efficient storage and search through hash tables in Java. It uses an array linked list (or red and black tree) structure, first obtain the hash value through the hashCode of the key, and then map it to the array index after processing by the hash function to reduce conflicts; 1. When a hash collision occurs, use the linked list to connect multiple key-value pairs; 2. Since JDK8, when the length of the linked list exceeds 8, it is converted to a red and black tree to improve search efficiency; 3. The default initial capacity is 16 and the load factor is 0.75. When the number of elements exceeds the threshold, the capacity expansion is triggered, the array is doubled and the element position is recalculated; 4. Multi-threaded capacity expansion may lead to dead loops or data confusion. It is recommended to use ConcurrentHashMap in a concurrent environment.

Jun 25, 2025 am 09:49 AM

What is the `equals` method for strings?

Comparing string content in Java should use the equals() method instead of the == operator, because == only compares object references and not content. 1. Using == may lead to error results. For example, the newly created same string object will be judged to be unequal; 2. Equals() ensures the content consistency through character-by-character comparison, regardless of how the string is created; 3. Note that equals() is case sensitive and null exceptions must be avoided when processing null; 4. EqualsIgnoreCase() can be used for ignoring case comparison; 5. Others such as Objects.equals(a,b) can elegantly handle null values. Therefore, always use equals() to compare the actual inside of a string

Jun 25, 2025 am 09:21 AM

What is a List?

List in programming is a basic data structure used to store multiple ordered elements and supports different types and dynamic modifications. For example, lists in Python can be accessed through indexes and are suitable for frequent addition and deletion scenarios; in daily life, List is used to clearly list tasks or items, such as to-do items, and is often sorted by priority or time; the difference between List and Array and Set is its dynamicity, flexibility and allows for duplicate values.

Jun 25, 2025 am 09:01 AM

How to use a try-catch block?

The use of the try-catch block is to handle possible exceptions when the program runs, so that the program can handle errors gracefully instead of crashing directly. Common application scenarios include calling external interfaces, reading and writing files, parsing data formats, and user input verification. The basic structure is to execute code that may occur in the try block. The catch block catches and handles exceptions. Some languages ??support the use of multiple catch blocks according to the error type for differentiation processing. Notes include avoiding abuse, non-empty catch blocks, finally cleaning resources, and logging error logs. The example shows how JSON parsing failures and file reading errors are handled, and emphasizes that rational use can improve program robustness and debugging efficiency.

Jun 25, 2025 am 08:17 AM

What is the Factory pattern?

Factory mode is used to encapsulate object creation logic, making the code more flexible, easy to maintain, and loosely coupled. The core answer is: by centrally managing object creation logic, hiding implementation details, and supporting the creation of multiple related objects. The specific description is as follows: the factory mode handes object creation to a special factory class or method for processing, avoiding the use of newClass() directly; it is suitable for scenarios where multiple types of related objects are created, creation logic may change, and implementation details need to be hidden; for example, in the payment processor, Stripe, PayPal and other instances are created through factories; its implementation includes the object returned by the factory class based on input parameters, and all objects realize a common interface; common variants include simple factories, factory methods and abstract factories, which are suitable for different complexities.

Jun 24, 2025 pm 11:29 PM

What is type casting?

There are two types of conversion: implicit and explicit. 1. Implicit conversion occurs automatically, such as converting int to double; 2. Explicit conversion requires manual operation, such as using (int)myDouble. A case where type conversion is required includes processing user input, mathematical operations, or passing different types of values ??between functions. Issues that need to be noted are: turning floating-point numbers into integers will truncate the fractional part, turning large types into small types may lead to data loss, and some languages ??do not allow direct conversion of specific types. A proper understanding of language conversion rules helps avoid errors.

Jun 24, 2025 pm 11:09 PM

What are static methods in interfaces?

StaticmethodsininterfaceswereintroducedinJava8toallowutilityfunctionswithintheinterfaceitself.BeforeJava8,suchfunctionsrequiredseparatehelperclasses,leadingtodisorganizedcode.Now,staticmethodsprovidethreekeybenefits:1)theyenableutilitymethodsdirectly

Jun 24, 2025 pm 10:57 PM

How does JIT compiler optimize code?

The JIT compiler optimizes code through four methods: method inline, hot spot detection and compilation, type speculation and devirtualization, and redundant operation elimination. 1. Method inline reduces call overhead and inserts frequently called small methods directly into the call; 2. Hot spot detection and high-frequency code execution and centrally optimize it to save resources; 3. Type speculation collects runtime type information to achieve devirtualization calls, improving efficiency; 4. Redundant operations eliminate useless calculations and inspections based on operational data deletion, enhancing performance.

Jun 24, 2025 pm 10:45 PM

Difference between HashMap and Hashtable?

The difference between HashMap and Hashtable is mainly reflected in thread safety, null value support and performance. 1. In terms of thread safety, Hashtable is thread-safe, and its methods are mostly synchronous methods, while HashMap does not perform synchronization processing, which is not thread-safe; 2. In terms of null value support, HashMap allows one null key and multiple null values, while Hashtable does not allow null keys or values, otherwise a NullPointerException will be thrown; 3. In terms of performance, HashMap is more efficient because there is no synchronization mechanism, and Hashtable has a low locking performance for each operation. It is recommended to use ConcurrentHashMap instead.

Jun 24, 2025 pm 09:41 PM

What is a `static` block?

AstaticblockinJavaisusedtoinitializestaticvariablesorperformone-timesetuptaskswhenaclassisloaded.1.Itexecutesoncebeforeanyobjectsarecreatedorstaticmethodscalled.2.It'susefulforcomplexinitializationlogiclikeloadingfilesorconnectingtosystems.3.Definedw

Jun 24, 2025 pm 08:33 PM

What is synchronization?

Synchronizationistheprocessofcoordinatingtwoormorethingstostayaligned,whetherdigitalorphysical.Intechnology,itensuresdataconsistencyacrossdevicesthroughcloudserviceslikeGoogleDriveandiCloud,keepingcontacts,calendarevents,andbookmarksupdated.Outsidete

Jun 24, 2025 pm 08:21 PM

Synchronize concurrent

What is the `final` keyword for variables?

InJava,thefinalkeywordpreventsavariable’svaluefrombeingchangedafterassignment,butitsbehaviordiffersforprimitivesandobjectreferences.Forprimitivevariables,finalmakesthevalueconstant,asinfinalintMAX_SPEED=100;wherereassignmentcausesanerror.Forobjectref

Jun 24, 2025 pm 07:29 PM

variable final