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What is the Optional class in Java 8 and how to use it?

The Optional class solves the problem that null values cause NullPointerException in Java. It reduces the risk of ignoring null checks by forcing explicit processing of whether the value exists. The creation methods include: 1.Optional.of(value); 2.Optional.ofNullable(value); 3.Optional.empty(). The methods to get the value are: 1. isPresent() combined with get(); 2.orElse(default); 3.ifPresent(action); 4.orElseGet(supplier). Applicable scenarios

Jul 22, 2025 am 01:50 AM

Optimizing Java for Real-time Systems

TooptimizeJavaforreal-timesystems,choosealow-pausegarbagecollectorlikeZGCorShenandoah,minimizeobjectallocationbyreusingobjectsandusingprimitives,tuneJITbehaviorthroughwarm-upandcompilationmonitoring,andoptionallyuseReal-TimeJavaextensionslikeRTSJforh

Jul 22, 2025 am 01:49 AM

java real time system

Java JNI (Java Native Interface) Performance Considerations

The key to JNI performance optimization is to reduce the number of cross-language calls, reduce data conversion overhead, and reasonably manage life cycles and threads. 1. Avoid frequent JNI calls and merge multiple calls into one processing; 2. Try to execute loop logic at the native layer instead of Java to control loop body; 3. Transfer the entire array at one time when passing an array and process it in native; 4. Use efficient string and array conversion methods, such as GetStringUTFChars and GetPrimitiveArrayCritical; 5. Release local references in time to prevent memory leakage; 6. Avoid creating a large number of temporary Java objects in native; 7. Each thread uses independent JNIEnv for a long time

Jul 22, 2025 am 01:40 AM

Java Cryptography for Secure Communication

Four key points must be followed to realize Java secure communication: first, use SSL/TLS to establish a secure connection, and implement it through HttpsURLConnection or SSLSocket, and SSL handshake is handled by default. Custom trust databases need to configure SSLContext, and certificate verification cannot be disabled; second, choose symmetric and asymmetric encryption, AES encrypted data, RSA encryption keys, to ensure speed and security; third, use digital signatures to ensure data integrity, sender private key signature, receiver public key verification, and commonly use SHA256withRSA and other algorithms; finally, use SecureRandom to generate random numbers to avoid fixed values, combine with key management services to protect key security, regularly replace and correctly select

Jul 22, 2025 am 01:38 AM

Java Memory Profiling with Eclipse MAT

To quickly locate Java memory issues, analyzing heap dumps using EclipseMAT is key. 1. Automatically generate heapdump when using jmap, JVisualVM or OOM; 2. After opening the file, check Histogram, DominatorTree and LeakSuspects to locate suspicious objects; 3. Analyze the GCRoots reference chain to confirm whether the leak is caused by invalid references; 4. Use CompareBasket to compare snapshots to observe memory trends; 5. Pay attention to the loading performance of large files and the display of array types. Mastering these operations can effectively troubleshoot most memory bottlenecks.

Jul 22, 2025 am 01:21 AM

what are generics in java

Generics are used in Java to improve code flexibility and type safety. It allows classes, interfaces, and methods to use type parameters, allowing the caller to specify specific types when using them, thereby avoiding runtime type conversion errors. For example, ArrayList ensures that the list only stores strings, and the compiler will report an error when adding a non-String type. 1. Generics avoid cast type conversion and reduce the risk of ClassCastException; 2. Compatibility is achieved through type erasure, but runtime type judgment cannot be performed; 3. Support wildcards and boundaries to define type ranges, such as List

Jul 22, 2025 am 01:20 AM

Java Cryptography Architecture (JCA) Deep Dive

JCA is the core of the Java security system and provides a unified encryption interface. It abstracts encryption functions through the SPI framework and is specifically implemented by Provider, such as SunJCE, BC, etc. Common categories include KeyPairGenerator, Cipher, MessageDigest, etc. When using it, you need to pay attention to the order of the Provider registration, avoid hard-coded names, correct format algorithm names, and no reuse of IVs and security management keys.

Jul 22, 2025 am 12:50 AM

Java Virtual Machine Crash Analysis and Debugging

JVM crashes are usually caused by native layer problems such as JNI errors, JVMbugs, insufficient resources, or third-party library conflicts. Analyze the hs_err_pid file to locate the source of the problem and combine it with GDB, Valgrind and other tools to check it. 1. Common reasons include JNI call errors, JVM itself bugs, system resource exhaustion and third-party library conflicts; 2. The hs_err_pid file contains crash thread information, stack trace, register status and native library list, and specific functions can be located through "Problematicframe"; 3. Analysis tools include GDB loading coredump, jstack/jmap grabbing snapshots, and Valgrind detecting memory errors

Jul 22, 2025 am 12:49 AM

Java Performance Tuning for High-Concurrency Systems

High-concurrency systems need to optimize Java performance from JVM tuning, thread management, GC strategy and other aspects. 1. The default values should be avoided when tuning JVM parameters, and the heap memory and young generation size should be reasonably set. It is recommended to use G1 or ZGC and enable GC logs; 2. The thread pool configuration needs to adjust the number of threads according to the task type, and select appropriate queue and rejection strategies; 3. Reduce lock competition and give priority to using lock-free structures, reduce lock granularity, and avoid internal lock-consumption operations; 4. Database connections and caches need to combine connection pools and cache policies to prevent external dependencies from becoming bottlenecks. These methods can effectively improve system stability and performance.

Jul 22, 2025 am 12:40 AM

java performance High concurrency system

How to create a new Thread in Java?

There are mainly the following ways to create threads in Java: 1. Inherit the Thread class and rewrite the run() method. This method is simple but not recommended because it will restrict the inheritance of the class; 2. Implement the Runnable interface and pass its instance into the Thread constructor, which is more flexible and commonly used, suitable for designs that separate tasks and threads; 3. Use Lambda expressions (Java8) to make the code concise and clear, and suitable for simple tasks; 4. Use a thread pool (ExecutorService), which can reuse threads, reduce overhead, and facilitate concurrent control. The choice of the appropriate method depends on the specific application scenario. The first two types of learning or simple tasks are available. For project development, it is recommended to use Lambda and thread pool.

Jul 22, 2025 am 12:04 AM

java pass by value or pass by reference

Java is passed by value, whether it is a primitive type or an object. For basic types, the actual value of the variable is passed, and modification within the method does not affect the external variable; for objects, a copy of the reference address is passed, and the object content can be modified within the method but the external reference point cannot be changed. For example: modifying the basic type parameters does not affect the original value; modifying the object properties will affect the original object, but letting the parameters point to the new object is invalid. If you need to change the reference itself, you can implement it indirectly by arrays or wrapper classes.

Jul 21, 2025 am 03:43 AM

How to copy a file in Java?

There are three ways to copy files in Java. The first is to use FileInputStream and FileOutputStream, which is suitable for Java7 and earlier versions. By reading byte streams and writing to the target file, it is suitable for understanding the underlying principles but limited performance; the second is to use Files.copy(), which is recommended for Java7 and above versions. The code is concise and efficient, and FileChannel is used internally and supports whether to overwrite existing files; the third is to use ApacheCommonsIO tool class, which is suitable for projects that have been introduced to this library. It has simple operation but requires third-party dependencies to be added. The selection method should be determined based on the Java version, whether third-party libraries are allowed and specific performance requirements.

Jul 21, 2025 am 03:43 AM

how to create a thread in java using runnable interface

A common way to create threads in Java is to implement the Runnable interface. 1. Create a class to implement Runnable and override the run() method; 2. Create a Thread object and pass the Runnable instance in; 3. Call start() to start the thread. Compared to inheriting Thread, Runnable avoids single inheritance restrictions, separates tasks from threads, and better supports thread pooling. Java8 can use Lambda to simplify the code. Note that run() does not start threads, the same Runnable can be multiplexed by multiple threads, and start() cannot be called repeatedly after the thread is started.

Jul 21, 2025 am 03:42 AM

what is object cloning in java

Java's clone() method implements shallow copying by default when copying objects. If you need deep copying, you need to manually process nested objects. 1. To call clone(), you need to implement the Cloneable interface and override the clone() method. 2. Shallow copy only copies the primitive type values, and object fields copy references. 3. Deep copy requires manually cloning nested objects to avoid reference sharing. 4. Common alternatives include replica constructors and static factory methods for their clearer and safer. 5. Pay attention to exception handling and visibility modifiers when using clone().

Jul 21, 2025 am 03:42 AM