Why Does `Integer` Equality Sometimes Return `false` in Java?

Integers Caching in Java: Understanding the Optimization

Recent observations have brought up confusion regarding the behavior of Integer objects in Java. A code example demonstrates that the equality operator returns "false" for two Integer instances equal to 1000 but "true" for two instances equal to 100.

This seeming paradox stems from Java's caching mechanism for integers. To optimize performance and reduce memory footprint, the Java Virtual Machine (JVM) caches Integer objects for values between -128 and 127. This means that references to Integer instances within this range are always the same.

Therefore, in the second code snippet, where the Integer instances represent the value 100, both "c" and "d" point to the same cached object, resulting in "true" when comparing their equality. However, for values outside this range, such as 1000, different Integer objects are created, hence the "false" comparison result.

This optimization affects performance by reducing memory usage, leading to more efficient cache utilization. It also eliminates the overhead of creating new objects for frequently used integers, making code execution faster.

Further research on this topic can be found in the following resources:

• [Oracle's Java Performance Tuning Guidelines](https://docs.oracle.com/javase/7/docs/technotes/guides/vm/performance-tuning-6.html#integer_caching)
• [Optimization of Integer Arithmetic in Java and C ](https://coincidental.com/research/number-boxes.pdf)

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