What are the methods to improve the performance of java programs?

1. Try to specify the final modifier of the class. Classes with final modifiers cannot be derived.

In the Java core API, there are many applications of final. Examples, such as java.lang.String. Specifying final for the String class prevents people from overriding the length() method. In addition, if a class is designated as final, all methods of the class will be final. The Java compiler will look for opportunities to inline all final methods.

2. Try to reuse objects

Especially when using String objects, StringBuffer should be used instead when string connection occurs. Since the system not only needs to spend time generating objects, but may also need to spend time garbage collecting and processing these objects in the future, generating too many objects will have a great impact on the performance of the program.

3. Try to use local variables

The parameters passed when calling the method and the temporary variables created during the call are saved in the stack (Stack). Other variables, such as static variables and instance variables etc., are all created in the Heap and are slower. In addition, depending on the specific compiler/JVM, local variables may be further optimized.

4. Do not initialize variables repeatedly

By default, when calling the constructor of a class, Java will initialize variables to certain values: all objects are set to null, integer variables ( byte, short, int, long) are set to 0, float and double variables are set to 0.0, and logical values ​​are set to false. This should be especially noted when a class is derived from another class, because when an object is created using the new keyword, all constructors in the constructor chain will be automatically called.

5. In the development of JAVA ORACLE application system, the SQL statements embedded in Java should be in uppercase as much as possible to reduce the parsing burden of the ORACLE parser.

6. During Java programming, be careful when performing database connections and I/O stream operations. After use, even close to release resources. Because operations on these large objects will cause a lot of system overhead.

7. Since the JVM has its own GC mechanism, it does not require too much consideration by program developers. This reduces the burden on developers to a certain extent, but it also misses hidden dangers. Excessive object creation will cause It consumes a large amount of system memory and can cause memory leaks in severe cases. Therefore, it is of great significance to ensure the timely recycling of expired objects.

The condition for JVM to recycle garbage is: the object is no longer referenced; however, the JVM's GC is not very smart, and even if the object meets the conditions for garbage collection, it may not be recycled immediately. Therefore, it is recommended that we manually set it to null after using the object.

8. When using synchronization mechanism, try to use method synchronization instead of code block synchronization.

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