When Should You Use Java String Interning and What Are the Potential Drawbacks?

Java String Interning: An Explanation and Considerations

Java String interning is a technique that involves sharing a common memory space for string objects with identical content. By calling the String.intern() method on strings, you can ensure that strings with the same value point to the same object in memory.

When to Use String Interning

String interning is particularly useful when dealing with large numbers of duplicate string values. For example, consider a list of people's names where "John" appears multiple times. By interning these strings, you can reduce the memory footprint by ensuring that only a single "John" object is allocated.

Considerations

While string interning can save memory, it is important to be aware of potential drawbacks. The strings interned by JVM are stored in a special memory pool called the permanent generation. This pool has a limited size compared to the heap, where most objects are allocated. Therefore, excessive use of interning can result in OutOfMemory errors in the permanent generation.

Changes in Java 7

In Java 7, a significant change was introduced regarding string interning. Previously, interned strings were stored in the permanent generation. However, from Java 7 onwards, interned strings are stored in the main heap alongside other objects. This change alleviates the potential for OutOfMemory errors related to excessive string interning.

Conclusion

String interning can be a valuable technique for reducing memory usage. However, it is essential to use it judiciously and consider the potential impact on the permanent generation memory pool (prior to Java 7) or the main heap (Java 7 and later). By understanding these considerations, you can effectively utilize string interning to optimize the memory performance of your Java applications.

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