> For the complete documentation index, see [llms.txt](https://docs.xplatform.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.xplatform.com/talon/developing-applications/authoring-user-code/message-processing/processing-messages/handling-messages/coding-for-zero-garbage/array-accessors.md).

# Array Accessors

Zero garbage array accessors enable iteration over message array fields without allocating iterator objects. They use the XIterator pattern to provide zero-garbage traversal of arrays.

## Overview

When a message or state object contains an array field, traditional Java iteration using `for-each` or `Iterator` creates temporary objects that contribute to garbage. Talon's zero garbage array accessors provide a way to iterate over arrays without any allocations.

## XIterator Pattern

The XIterator pattern provides zero-garbage iteration through reusable iterator objects. When ADM generates code for array fields, it produces `iterateXXX()` methods that return an XIterator.

## Generated Methods

For an array field declared as:

```xml
<message name="Order">
  <OrderLine name="lines" array="true"/>
</message>
```

The ADM code generator produces:

| Method                   | Description                                     |
| ------------------------ | ----------------------------------------------- |
| `getLines()`             | Returns a List view of the array (allocates)    |
| `getLines(int index)`    | Returns the element at the specified index      |
| `iterateLines()`         | Returns an XIterator for zero-garbage iteration |
| `addLine(OrderLine)`     | Adds an element to the array                    |
| `removeLines(int index)` | Removes element at index                        |
| `clearLines()`           | Removes all elements                            |

## Zero Garbage Iteration

Use the XIterator for zero-garbage array traversal:

```java
@EventHandler
public void onOrder(Order order) {
    // Zero garbage iteration
    XIterator<OrderLine> iter = order.iterateLines();
    while (iter.hasNext()) {
        OrderLine line = iter.next();
        // Process line
        double value = line.getQuantity() * line.getPrice();
    }
}
```

The XIterator is reused across calls and does not allocate.

## Use Cases

**Filtering**:

```java
XIterator<OrderLine> iter = order.iterateLines();
while (iter.hasNext()) {
    OrderLine line = iter.next();
    if (line.getQuantity() > 100) {
        // Process large orders
    }
}
```

**Aggregation**:

```java
double total = 0.0;
XIterator<OrderLine> iter = order.iterateLines();
while (iter.hasNext()) {
    OrderLine line = iter.next();
    total += line.getQuantity() * line.getPrice();
}
```

**Modifying Elements**:

```java
XIterator<OrderLine> iter = order.iterateLines();
while (iter.hasNext()) {
    OrderLine line = iter.next();
    // Modify in place
    line.setPrice(line.getPrice() * 1.1); // Apply 10% markup
}
```

## Comparison with Standard Java Iteration

**Standard (allocates)**:

```java
// Creates iterator object
for (OrderLine line : order.getLines()) {
    processLine(line);
}
```

**Zero Garbage**:

```java
// Reuses iterator object
XIterator<OrderLine> iter = order.iterateLines();
while (iter.hasNext()) {
    OrderLine line = iter.next();
    processLine(line);
}
```

The zero-garbage approach reuses the same XIterator instance on each call to `iterateXXX()`, eliminating allocations.

## See Also

* [Coding for Zero Garbage](/talon/developing-applications/authoring-user-code/message-processing/processing-messages/handling-messages/coding-for-zero-garbage.md) - Overview of zero garbage techniques
* [Embedded Entities](/talon/developing-applications/authoring-user-code/message-processing/processing-messages/handling-messages/coding-for-zero-garbage/embedded-entities.md) - Lifecycle-managed objects for complex messages
* [Application Object Pooling](/talon/developing-applications/authoring-user-code/message-processing/processing-messages/handling-messages/coding-for-zero-garbage/application-object-pooling.md) - Creating custom pooled objects