Why Do Java\'s Integer Wrapper Objects Share Instances Between -128 and 127?

Integer Wrapper Objects: Shared Instances within a Specific Value Range

Java's integer wrapper object, Integer, has a peculiar behavior where it shares the same instance for values within a particular range. Understanding this characteristic is essential for effective object management.

Why Objects Share Instances within the Range of -128 to 127

According to the Java Language Specification (JLS), integer wrapper objects in the range of -128 to 127 share the same instance. Any two boxing conversions of the same value within this range will always return identical references (object1 == object2 will evaluate to true).

This behavior is driven by two factors: practicality and efficiency. Caching these commonly used values optimizes performance, particularly on resource-constrained devices. Additionally, it enables predictable object manipulation for frequently encountered values.

Variations Outside the Specified Range

However, for values outside the range of -128 to 127, such as 128 seen in the example, different instances of Integer objects are created. This fundamental distinction highlights the importance of understanding the specific range where instance sharing occurs.

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