java - Why there is a local variable referencing value array in String#hashCode? -


what purpose of copying value reference val variable, oppose using directly?

public int hashcode() {     int h = hash;     if (h == 0 && value.length > 0) {         char val[] = value;    // private final char value[];          (int = 0; < value.length; i++) {             h = 31 * h + val[i];         }         hash = h;     }     return h; }

this performance optimization according martin buchholz

copying locals produces smallest bytecode

see also:
in arrayblockingqueue, why copy final member field local final variable?

+----------------------+----------------------------+------------------------------+ | h = 31 * h + val[i]; | h = 31 * h + value[i];     | hash = 31 * hash + value[i]; | +----------------------+----------------------------+------------------------------+ | linenumber 1471 l7   | linenumber 14 l6           | linenumber 13 l4             | | bipush 31            | bipush 31                  | aload 0                      | | iload 1              | iload 1                    | bipush 31                    | | imul                 | imul                       | aload 0                      | | aload 2              | aload 0                    | getfield string.hash :     | | iload 3              | getfield string.value : [c | imul                         | | caload               | iload 2                    | aload 0                      | | iadd                 | caload                     | getfield string.value : [c   | | istore 1             | iadd                       | iload 1                      | |                      | istore 1                   | caload                       | |                      |                            | iadd                         | |                      |                            | putfield string.hash :     | +----------------------+----------------------------+------------------------------+

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