Why Doesn't Modifying a For-Each Loop's Iteration Variable Change the Underlying Array in Java?

Why Modifying the Iteration Variable in a For-Each Loop Doesn't Alter Underlying Data

In Java, the enhanced for-each loop is a convenient syntax for iterating over arrays or collections. However, a common misconception arises when attempting to modify the underlying data within the loop.

Consider the following code snippet:

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

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

Despite the if-else block attempting to replace all occurrences of 'o' with 'a', the result remains "boss". Why is this the case?

The key to understanding this behavior lies in the nature of the iteration variable in a for-each loop. When iterating over an array using the for-each syntax, the iteration variable (c in this case) is simply a copy of the array element at the current index. Any changes made to the iteration variable do not propagate back to the original array.

To modify the underlying data, it is necessary to explicitly access and modify the array element itself. This can be achieved using the standard for loop syntax:

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

In this revised code, the iteration variable i keeps track of the current index in the array, while array[i] accesses the actual element at that index. Assigning to array[i] directly will modify the content of the array.

Therefore, when working with arrays or collections using the for-each loop syntax, it is crucial to remember that modifying the iteration variable alone does not alter the underlying data. To make permanent changes to the data, it is necessary to explicitly access and modify the elements within the collection using standard loop syntax or other appropriate methods.

The above is the detailed content of Why Doesn't Modifying a For-Each Loop's Iteration Variable Change the Underlying Array in Java?. For more information, please follow other related articles on the PHP Chinese website!