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Although we won’t go in deeper details on asynchronous programming in Java, remember to handle failures of asynchronous tasks. It’s easy to overlook them and have errors go unnoticed.
Copy file name to clipboardExpand all lines: docs/reference/api-conventions/building-objects.md
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All data types in the Java API Client are immutable. Object creation uses the [builder pattern](https://www.informit.com/articles/article.aspx?p=1216151&seqNum=2) that was popularized in **Effective Java** in 2008.
Note that a builder should not be reused after its `build()` method has been called.
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Although this works nicely, having to instantiate builder classes and call the `build()` method is a bit verbose. So every property setter in the Java API Client also accepts a lambda expression that takes a newly created builder as a parameter and returns a populated builder. The snippet above can also be written as:
This approach allows for much more concise code, and also avoids importing classes (and even remembering their names) since types are inferred from the method parameter signature.
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Note in the above example that builder variables are only used to start a chain of property setters. The names of these variables are therefore unimportant and can be shortened to improve readability:
Builder lambdas become particularly useful with complex nested queries like the one below, taken from the [intervals query API documentation](elasticsearch://reference/query-languages/query-dsl/query-dsl-intervals-query.md).
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This example also highlights a useful naming convention for builder parameters in deeply nested structures. For lambda expressions with a single argument, Kotlin provides the implicit `it` parameter and Scala allows use of `_`. This can be approximated in Java by using an underscore or a single letter prefix followed by a number representing the depth level (i.e. `_0`, `_1`, or `b0`, `b1` and so on). Not only does this remove the need to create throw-away variable names, but it also improves code readability. Correct indentation also allows the structure of the query to stand out.
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a -> a.histogram(h -> h.field("price")))
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);
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```
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% :::include::end -- do not remove
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## List and map values are never `null`[_list_and_map_values_are_never_null]
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If you ever need to distinguish between a missing (undefined) optional collection and an effectively-empty collection returned by {{es}}, the `ApiTypeHelper` class provides a utility method to distinguish them:
1. when calling `withJson()` on data structures that have generic type parameters, these generic types will be considered to be `JsonData`.
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You can combine `withJson()` with regular calls to setter methods. The example below loads the query part of a search request from a `String` and programmatically adds an aggregation.
The `withJson()` methods are partial deserializers: the properties loaded from the JSON will set property values or replace the previous ones, but will not reset other properties not found in the JSON input. You can use this to combine multiple JSON snippets to build complex search requests. In the example below, we combine separate definitions of a query that selects some documents and an aggregation that is run on the results of this query.
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