Why Doesn't Modifying a Character in a Java For-Each Loop Change the Original Array?

Diving into the Iteration Dilemma: Why Foreach Loop Assignments Don't Alter Underlying Data

Despite the intuitive appeal of directly modifying elements within a foreach loop, as seen in this Java snippet:

String boss = "boss";
char[] array = boss.toCharArray();

for(char c : array)
{
 if (c== 'o')
     c = 'a'; 
}
System.out.println(new String(array)); //Unexpected result: "boss"

the code surprisingly yields "boss" instead of the expected "bass."

Unveiling the Copy

The key to understanding this paradox lies in the nature of the iteration variable "c." Contrary to popular belief, "c" represents a mere copy of the array element at hand. Modifying "c" has no bearing on the original array contents.

Array Modification Demystified

To genuinely alter the array, explicit intervention is necessary:

for (int i = 0; i < array.length; i++) {
    if (array[i] == 'o') {
        array[i] = 'a';
    }
}

Here, the code accesses and modifies the actual array elements, resulting in the array being updated to reflect the desired changes.

Understanding JLS Interpretation

The Java Language Specification (JLS) interprets the original code as equivalent to:

for (int i = 0; i < array.length; i++) {
    char c = array[i];
    if (c == 'o') {
        c = 'a'; 
    }
}

This decomposition emphasizes that "c" is merely a copy that cannot influence the array.

In essence, foreach loops provide a streamlined means of iterating over collections without interfering with their underlying structure. Direct array modification requires explicitly working with the array index and elements.

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