## Is Precomputing Array Length in Java Really Necessary for Optimization?

Is Array.length Computationally Costly?

Many developers have observed a pattern where developers utilize for-each loops with a precomputed array length to optimize their code. By precomputing the length and storing it in a variable, they avoid calling the length() method for collections, which incurs a performance penalty. However, does this optimization apply to arrays?

Array.length: A Constant Time Operation

Contrary to intuition, calling array.length in Java is not a performance-intensive operation. Unlike collections where size() involves counting elements, array.length is a public final member of the array object. Accessing it is no slower than reaching a local variable.

JIT Compiler Optimization

Modern JIT compilers, such as those in OpenJDK, often optimize calls to array.length. They eliminate the lookup and fetching of the length property, resulting in faster execution.

Exceptions to Optimization

While the JIT compiler typically optimizes array.length calls, there are instances where it may not be able to do so. These include:

• Debugging the enclosing method where optimization is disabled.
• Loops with excessive local variables that force the JIT compiler to spill registers.

Confirmation

You can verify this behavior by examining the JIT compiled native code or by reviewing the source code of the JIT compiler in OpenJDK. Most cases will exhibit negligible performance differences between using a precomputed length variable and accessing array.length directly.

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