## Is Calling array.length Really Expensive? A Look at the Cost of Array Size Access.

Understanding the Cost of Calling array.length

While updating for loops to for-each loops, it is often observed that instantiating the loop variable with array.length enhances performance for collections by eliminating the need for the size() method call within each iteration. However, this raises the question: what is the cost of invoking array.length compared to using a regular variable?

Answer: Constant Time Operation

Contrarily, calling array.length is an O(1) operation or a constant time operation. This means that accessing array.length, which behaves as a public final member of the array, is no slower than accessing a local variable. This is in stark contrast to method calls like size(), which involve additional overhead.

Modern JIT compilers typically optimize calls to array.length, effectively eliminating the cost. To verify this, examine the source code of the JIT compiler or request the JVM to export the JIT-compiled native code for inspection.

Exceptions to Optimization

It's important to note that in certain situations, JIT compilers may not be able to optimize away the cost of array.length:

• When debugging the enclosing method
• When the loop body contains an excessive number of local variables, leading to register spilling

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