introduction
Strings are one of the most commonly used data types in Java programming. Java's string intern mechanism is an important and often overlooked topic in string processing. This article will take you to deeply explore the principles and influencing factors of the string resident mechanism in Java.
What is the string residency mechanism?
The string resident mechanism refers to an optimization method adopted by the Java virtual machine (JVM) to improve performance and save memory. When creating a string object, the JVM checks whether a string with the same value already exists in the string constant pool (String Pool). If it exists, it will directly return the reference in the constant pool; if it does not exist, it will create a new string object in the constant pool and put its reference in the constant pool.
The principle of string persistence
The principle of the string resident mechanism mainly includes the following aspects:
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String constant pool: The string constant pool is a special memory area located in the method area for storing string literals and resident string objects. During compilation, all string literals are put into the string constant pool.
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The intern() method of the String class: The String class provides the intern() method, which is used to explicitly add a string object to the string constant pool. After calling the intern() method, if a string with the same value already exists in the constant pool, the reference in the constant pool will be returned directly; otherwise, the current string object will be added to the constant pool and the reference will be returned.
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String comparison: In Java, string comparison is usually done using the equals() method. For string literals enclosed in double quotes, the intern() method will be called automatically at compile time to add them to the string constant pool. For string objects created using the new keyword, you need to manually call the intern() method to add them to the constant pool.
Influencing factors of string residency
The application of the string resident mechanism will affect the performance and memory usage of the program, so the following points need to be paid attention to in actual development:
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Memory usage: String persistence can save memory, but it will also increase the footprint of the constant pool. If there are a large number of strings with the same value in the program, the constant pool may be too large, which will affect performance.
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String concatenation: String concatenation operations generate new string objects. If you use the "+" operator for splicing, a new string object will be generated in the heap; while using StringBuilder or StringBuffer for splicing will not generate a new string object, which is more efficient.
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Multi-threaded environment: Due to the shared nature of the string constant pool, multiple threads operating on strings at the same time may lead to some unexpected results. In a multi-threaded environment, it is recommended to use other methods of String or control synchronization by yourself to avoid potential problems.
in conclusion
The string resident mechanism is an important technology used to optimize performance and save memory in Java. Reasonable application can improve the execution efficiency of the program. A deep understanding of the string persistence mechanism is crucial to writing efficient and stable Java programs.
Through this article, we have a deeper understanding of the principle of the string resident mechanism in Java. Hope this knowledge can help you better understand string processing, and correctly apply the string residency mechanism in actual development.