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How to iterate over a Map in Java?

There are three common methods to traverse Map in Java: 1. Use entrySet to obtain keys and values at the same time, which is suitable for most scenarios; 2. Use keySet or values to traverse keys or values respectively; 3. Use Java8's forEach to simplify the code structure. entrySet returns a Set set containing all key-value pairs, and each loop gets the Map.Entry object, suitable for frequent access to keys and values; if only keys or values are required, you can call keySet() or values() respectively, or you can get the value through map.get(key) when traversing the keys; Java 8 can use forEach((key,value)-&gt

Jul 13, 2025 am 02:54 AM

java Map iteration

What is the 'static' keyword in Java?

InJava,thestatickeywordmeansamemberbelongstotheclassitself,nottoinstances.Staticvariablesaresharedacrossallinstancesandaccessedwithoutobjectcreation,usefulforglobaltrackingorconstants.Staticmethodsoperateattheclasslevel,cannotaccessnon-staticmembers,

Jul 13, 2025 am 02:51 AM

java static

Comparing Traditional Java IO with New IO (NIO)

Traditional IO is suitable for simple file reading and writing, while NIO is suitable for concurrent and non-blocking scenarios. 1. Traditional IO is blocking stream operation, suitable for small amounts of connections and sequential processing; 2. NIO is based on channels and buffers, supports non-blocking and multiplexing, suitable for high concurrency and random access; 3. NIO can memory map files, improving the processing efficiency of large files; 4. Traditional IO API is simple and easy to use, strong compatibility, and high NIO learning and debugging costs; 5. Choose according to performance requirements, if there is no bottleneck, there is no need to force replacement.

Jul 13, 2025 am 02:50 AM

nio java io

How to handle character encoding issues in Java?

To deal with character encoding problems in Java, the key is to clearly specify the encoding used at each step. 1. Always specify encoding when reading and writing text, use InputStreamReader and OutputStreamWriter and pass in an explicit character set to avoid relying on system default encoding. 2. Make sure both ends are consistent when processing strings on the network boundary, set the correct Content-Type header and explicitly specify the encoding with the library. 3. Use String.getBytes() and newString(byte[]) with caution, and always manually specify StandardCharsets.UTF_8 to avoid data corruption caused by platform differences. In short, by

Jul 13, 2025 am 02:46 AM

java Character Encoding

What is StampedLock in Java 8?

StampedLock is a high-performance read-write lock mechanism introduced by Java 8, supporting three modes: 1. The write lock is an exclusive lock; 2. The optimistic read is a lightweight attempt mechanism; 3. The read lock is a shared lock. Compared with ReentrantReadWriteLock, it improves concurrency performance through the stamp version stamp mechanism, which is especially suitable for scenarios where more reads and less writes, and avoids writing hunger. When using it, you should pay attention to details such as non-reentry, non-sharing of stamps, and exception handling. It is recommended to use it under high concurrency requirements.

Jul 13, 2025 am 02:40 AM

Comparable vs Comparator in Java

In Java, Comparable is used to define default sorting rules internally, and Comparator is used to define multiple sorting logic externally. 1.Comparable is an interface implemented by the class itself. It defines the natural order by rewriting the compareTo() method. It is suitable for classes with fixed and most commonly used sorting methods, such as String or Integer. 2. Comparator is an externally defined functional interface, implemented through the compare() method, suitable for situations where multiple sorting methods are required for the same class, the class source code cannot be modified, or the sorting logic is often changed. The difference between the two is that Comparable can only define a sorting logic and needs to modify the class itself, while Compar

Jul 13, 2025 am 02:31 AM

java Comparators

How to implement the Proxy design pattern in Java?

To implement the proxy design pattern in Java, you first need to define a common interface, then implement the real topic class, then create a proxy class to control access to real objects, and finally use the proxy in the main program. 1. Define the public interface Image to ensure that the proxy and real objects are interchangeable; 2. Implement the RealImage class to be responsible for the loading and display of actual images; 3. Create the ImageProxy class to implement lazy loading in its display method; 4. Use ImageProxy in the Main class to delay loading image resources and improve efficiency. This mode supports multiple uses such as security control, logging, or remote calls.

Jul 13, 2025 am 02:30 AM

How to implement the Decorator design pattern in Java?

How to implement the decorator design pattern in Java? You can extend object functions by defining component interfaces, creating specific components, building basic decorators, adding specific decorators, and using decorators to combine them. 1. Define the component interface Coffee, including cost() and description() methods; 2. Create a specific component SimpleCoffee to implement basic functions; 3. Build an abstract decorator class CoffeeDecorator to implement the same interface and hold component references; 4. Add specific decorators such as MilkDecorator and SugarDecorator to add new functions based on the original behavior; 5. Realize dynamic function expansion by nesting calls to combine decorators at runtime

Jul 13, 2025 am 02:29 AM

java Decorator pattern

What is a ReentrantLock in Java?

ReentrantLock provides more flexible thread control in Java than synchronized. 1. It supports non-blocking acquisition locks (tryLock()), lock acquisition with timeout (tryLock(longtimeout, TimeUnitunit)) and interruptible wait locks; 2. Allows fair locks to avoid thread hunger; 3. Supports multiple condition variables to achieve a more refined wait/notification mechanism; 4. Need to manually release the lock, unlock() must be called in finally blocks to avoid resource leakage; 5. It is suitable for scenarios that require advanced synchronization control, such as custom synchronization tools or complex concurrent structures, but synchro is still recommended for simple mutual exclusion requirements.

Jul 13, 2025 am 02:14 AM

java

Java convert String to int

There are two main ways to convert strings to integers in Java: use Integer.parseInt() or Integer.valueOf(). 1. Integer.parseInt() directly returns the int type, which is suitable for simple conversion, but cannot process non-pure numeric strings or strings with decimal points, and the spaces before and after will be automatically ignored; 2. Integer.valueOf() returns the Integer object, suitable for scenarios where a wrapper class is required. It calls parseInt() internally, and the behavior is consistent. NumberFormatException will be thrown when the conversion fails, so it is recommended to use it with try-catch and correct it before the conversion.

Jul 13, 2025 am 02:12 AM

java

How to implement a simple HTTP server in Java without using any frameworks?

ThisarticleexplainshowtoimplementabasicHTTPserverinJavausingonlybuilt-inclasses.1)UseServerSockettoopenaportandlistenforincomingconnections.2)ReadtherawHTTPrequestviaInputStreamandparseitsmethodandpath.3)GenerateanHTTPresponsewithheadersandbodyusingO

Jul 13, 2025 am 02:06 AM

Creating Custom Annotations in Java

The steps to create custom annotations in Java include: 1. Use the @interface keyword to define annotations and set properties; 2. Use meta annotations such as @Retention and @Target to control the annotation life cycle and usage range; 3. Process annotations through reflection or framework to achieve logging, parameter verification and other functions; 4. Pay attention to member variable type restrictions and retention policy settings. For example, defining a @LogExecution annotation requires specifying it to be retained at runtime and applied to the method, and then reading the annotation through reflection or AOP mechanism and executing the corresponding logic, making the code more concise and efficient.

Jul 13, 2025 am 02:05 AM

What is structured concurrency in Java?

StructuredconcurrencyinJavasolvesthecomplexityofmanagingmultipleconcurrenttasksbygroupingthemintoasingleunitforcleanerhandling.1)Itsimplifieserrorpropagation,cancellation,andcoordination,especiallywhendealingwithexceptionsorwaitingforresults.2)Itwork

Jul 13, 2025 am 02:02 AM

java Structured concurrency

Factory design pattern in Java example

The factory pattern is to encapsulate object creation logic through a factory class, so that the caller does not need to care about the specific implementation class. 1. Define the unified behavior specification of interface Shape; 2. Create Circle and Rectangle implementation classes; 3. Write ShapeFactory factory class to return different instances according to parameters; 4. Use the factory class to obtain objects and call methods. This mode is suitable for scenarios where object creation is complex, the type is often changed, or the principle of opening and closing is required. It can effectively decouple the caller and specific classes and reduce maintenance costs.

Jul 13, 2025 am 01:59 AM