thenReturn() method in Mockito example

HashMap implements key-value pair storage through hash tables in Java, and its core lies in quickly positioning data locations. 1. First use the hashCode() method of the key to generate a hash value and convert it into an array index through bit operations; 2. Different objects may generate the same hash value, resulting in conflicts. At this time, the node is mounted in the form of a linked list. After JDK8, the linked list is too long (default length 8) and it will be converted to a red and black tree to improve efficiency; 3. When using a custom class as a key, the equals() and hashCode() methods must be rewritten; 4. HashMap dynamically expands capacity. When the number of elements exceeds the capacity and multiplies by the load factor (default 0.75), expand and rehash; 5. HashMap is not thread-safe, and Concu should be used in multithreaded

Virtual threads have significant performance advantages in highly concurrency and IO-intensive scenarios, but attention should be paid to the test methods and applicable scenarios. 1. Correct tests should simulate real business, especially IO blocking scenarios, and use tools such as JMH or Gatling to compare platform threads; 2. The throughput gap is obvious, and it can be several times to ten times higher than 100,000 concurrent requests, because it is lighter and efficient in scheduling; 3. During the test, it is necessary to avoid blindly pursuing high concurrency numbers, adapting to non-blocking IO models, and paying attention to monitoring indicators such as latency and GC; 4. In actual applications, it is suitable for web backend, asynchronous task processing and a large number of concurrent IO scenarios, while CPU-intensive tasks are still suitable for platform threads or ForkJoinPool.

TosetJAVA_HOMEonWindows,firstlocatetheJDKinstallationpath(e.g.,C:\ProgramFiles\Java\jdk-17),thencreateasystemenvironmentvariablenamedJAVA_HOMEwiththatpath.Next,updatethePATHvariablebyadding%JAVA\_HOME%\bin,andverifythesetupusingjava-versionandjavac-v

To correctly handle JDBC transactions, you must first turn off the automatic commit mode, then perform multiple operations, and finally commit or rollback according to the results; 1. Call conn.setAutoCommit(false) to start the transaction; 2. Execute multiple SQL operations, such as INSERT and UPDATE; 3. Call conn.commit() if all operations are successful, and call conn.rollback() if an exception occurs to ensure data consistency; at the same time, try-with-resources should be used to manage resources, properly handle exceptions and close connections to avoid connection leakage; in addition, it is recommended to use connection pools and set save points to achieve partial rollback, and keep transactions as short as possible to improve performance.

ServiceMesh is an inevitable choice for the evolution of Java microservice architecture, and its core lies in decoupling network logic and business code. 1. ServiceMesh handles load balancing, fuse, monitoring and other functions through Sidecar agents to focus on business; 2. Istio Envoy is suitable for medium and large projects, and Linkerd is lighter and suitable for small-scale trials; 3. Java microservices should close Feign, Ribbon and other components and hand them over to Istiod for discovery and communication; 4. Ensure automatic injection of Sidecar during deployment, pay attention to traffic rules configuration, protocol compatibility, and log tracking system construction, and adopt incremental migration and pre-control monitoring planning.

The key to implementing a linked list is to define node classes and implement basic operations. ①First create the Node class, including data and references to the next node; ② Then create the LinkedList class, implementing the insertion, deletion and printing functions; ③ Append method is used to add nodes at the tail; ④ printList method is used to output the content of the linked list; ⑤ deleteWithValue method is used to delete nodes with specified values and handle different situations of the head node and the intermediate node.

Create and use SimpleDateFormat requires passing in format strings, such as newSimpleDateFormat("yyyy-MM-ddHH:mm:ss"); 2. Pay attention to case sensitivity and avoid misuse of mixed single-letter formats and YYYY and DD; 3. SimpleDateFormat is not thread-safe. In a multi-thread environment, you should create a new instance or use ThreadLocal every time; 4. When parsing a string using the parse method, you need to catch ParseException, and note that the result does not contain time zone information; 5. It is recommended to use DateTimeFormatter and Lo

To improve the performance of Java collection framework, we can optimize from the following four points: 1. Choose the appropriate type according to the scenario, such as frequent random access to ArrayList, quick search to HashSet, and concurrentHashMap for concurrent environments; 2. Set capacity and load factors reasonably during initialization to reduce capacity expansion overhead, but avoid memory waste; 3. Use immutable sets (such as List.of()) to improve security and performance, suitable for constant or read-only data; 4. Prevent memory leaks, and use weak references or professional cache libraries to manage long-term survival sets. These details significantly affect program stability and efficiency.