# Apache Beam: ParDo

## Overview

If you want to apply a function which transforms each element in an input collection, you should use the `ParDo` transform.

## When You Should Use the ParDo Transform

Any time you want to perform some generic processing function on each element of a PCollection.

## How to Use the ParDo Transform

To perform processing on an element using the `ParDo` transform, all you need is a Java class which is a subclass of the `DoFn` abstract class which contains your transformation logic. Your subclass must override the `@processElement` function with the transformation code (see below examples).

## Example: Filter Word Counts with Max Length

```java
  // The input PCollection to ParDo.
  PCollection<String> words = ...;

  // Apply a ParDo that takes maxWordLengthCutOffView as a side input.
  PCollection<String> wordsBelowCutOff =
  words.apply(ParDo
      .of(new DoFn<String, String>() {
          public void processElement(ProcessContext c) {
            String word = c.element();
            int maxLength = 10;
            if (word.length() <= maxLength) {
              c.output(word);
            }
          }
      })
  );
```

## Conclusion

Check out other useful transforms from the [official Apache Beam documentation](https://beam.apache.org/documentation/transforms/java/overview/).