The most direct way to find the last occurrence of a substring in PHP is to use the strrpos() function. 1. Use strrpos() function to directly obtain the index of the last occurrence of the substring in the main string. If it is not found, it returns false. The syntax is strrpos($haystack,$needle,$offset=0). 2. If you need to ignore case, you can use the strripos() function to implement case-insensitive search. 3. For multi-byte characters such as Chinese, the mb_strrpos() function in the mbstring extension should be used to ensure that the character position is returned instead of the byte position. 4. Note that strrpos() returns f

The reason why header('Location:...') in AJAX request is invalid is that the browser will not automatically perform page redirects. Because in the AJAX request, the 302 status code and Location header information returned by the server will be processed as response data, rather than triggering the jump behavior. Solutions are: 1. Return JSON data in PHP and include a jump URL; 2. Check the redirect field in the front-end AJAX callback and jump manually with window.location.href; 3. Ensure that the PHP output is only JSON to avoid parsing failure; 4. To deal with cross-domain problems, you need to set appropriate CORS headers; 5. To prevent cache interference, you can add a timestamp or set cache:f

String is immutable, StringBuilder is mutable and non-thread-safe, StringBuffer is mutable and thread-safe. 1. Once the content of String is created cannot be modified, it is suitable for a small amount of splicing; 2. StringBuilder is suitable for frequent splicing of single threads, and has high performance; 3. StringBuffer is suitable for multi-threaded shared scenarios, but has a slightly lower performance; 4. Reasonably set the initial capacity and avoid using String splicing in loops can improve performance.

The COALESCE function is used to return the first non-null value in the parameter list and is suitable for processing NULL data. 1. The basic usage is to replace the NULL value, such as replacing the empty field with the default contact method; 2. It can be used to set the default value in aggregate query to ensure that 0 is returned instead of NULL when there is no data; 3. It can be used in conjunction with other functions such as NULLIF and IFNULL to enhance data cleaning and logical judgment capabilities.

Singleton design pattern in Java ensures that a class has only one instance and provides a global access point through private constructors and static methods, which is suitable for controlling access to shared resources. Implementation methods include: 1. Lazy loading, that is, the instance is created only when the first request is requested, which is suitable for situations where resource consumption is high and not necessarily required; 2. Thread-safe processing, ensuring that only one instance is created in a multi-threaded environment through synchronization methods or double check locking, and reducing performance impact; 3. Hungry loading, which directly initializes the instance during class loading, is suitable for lightweight objects or scenarios that can be initialized in advance; 4. Enumeration implementation, using Java enumeration to naturally support serialization, thread safety and prevent reflective attacks, is a recommended concise and reliable method. Different implementation methods can be selected according to specific needs

In PHP, the main difference between == and == is the strictness of type checking. The == operator performs type conversion when comparing, while === strictly checks the values ??and types without conversion. For example: "5"==5 returns true but "5"==5 returns false; 0==false is true but 0===false is false; null===0 is always false. You should use == when the type is independent or requires flexible comparison, such as user input processing; if the type must be consistent, such as the detection function returns false, validation null or boolean flag. It is recommended to use === first to avoid logic caused by type conversion

ThreadLocal is used in Java to create thread-private variables, each thread has an independent copy to avoid concurrency problems. It stores values ??through ThreadLocalMap inside the thread. Pay attention to timely cleaning when using it to prevent memory leakage. Common uses include user session management, database connections, transaction context, and log tracking. Best practices include: 1. Call remove() to clean up after use; 2. Avoid overuse; 3. InheritableThreadLocal is required for child thread inheritance; 4. Do not store large objects. The initial value can be set through initialValue() or withInitial(), and the initialization is delayed until the first get() call.

Adding comments to HTML can improve code readability and teamwork efficiency. Because HTML is a structured markup language and lacks obvious logical processes, it is difficult to understand the role of blocks when the page is complex. At this time, the comments can be used as "navigation" to answer questions such as module purpose, dynamic content source, form behavior, etc. Effective comments should be clear and concise, and use syntax. Common methods include explaining the purpose of the module (such as), marking precautions or to-do items (such as), marking code segment boundaries, and avoiding redundant explanations. Scenes suitable for annotation include page structure partitions, complex nesting areas, elements that require special processing and template reference locations. The unified annotation style is better when collaborating with teams, such as whether to use abbreviations, alignment, specific keywords, etc., which will help maintain and understand for a long time.