Why Does Java's Integer Class Cache Only Values Between -128 and 127?

Integer Class Caching: Exploring the Range of -128 to 127

The Integer class in Java boasts a cache that optimizes performance by storing frequently requested values. However, the specific range of -128 to 127 cached by Integer.valueOf() has raised some questions.

Why the Range -128 to 127?

This range is defined by the Java Language Specification (JLS), which mandates that int and short values within this range, when boxed into Integer objects, always produce identical references. This requirement ensures that for commonly used values, the desired behavior is achieved without compromising performance on small devices.

Rationale Behind the Cache Range

The cache optimizes performance by reducing the overhead associated with allocating new Integer objects for frequently used values. This is particularly beneficial for typical scenarios where numeric values tend to be centered around zero, making integers within the range -128 to 127 likely candidates for repeated use.

Caching Beyond the Specified Range

While the JLS requires caching within the range -128 to 127, implementations may extend this range to improve efficiency. The JVM option "-XX:AutoBoxCacheMax=" enables developers to specify a larger cache size, allowing for the caching of values beyond the default range. However, it's important to note that the availability of this option may vary across different JVM implementations.

Why Ignore Certain Values for Frequent Request Caching?

The JLS does not provide a definitive explanation for why it specifies a specific range for caching. However, it is possible that factors such as performance trade-offs and the need to address legacy code influenced the decision to define a specific range within which caching is guaranteed.

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