# Converting Method Arguments - General Rules

Having decided which method to call, Saxon has to convert the supplied XPath argument values to the Java objects required by this method.

If the expected type is `Object`, the supplied value must either be a singleton, or an empty sequence. If it is an empty sequence, null will be passed. If it is a singleton node, an instance of `net.sf.saxon.om.NodeInfo` will be passed. If it is a wrapped Java object, that Java object will be passed. If it is a singleton atomic value, the value will be converted to the nearest equivalent Java object: for example an `xs:boolean` becomes `java.lang.Boolean`, an `xs:string` becomes `java.lang.String`, and so on. An untyped atomic value is treated as a string. An `xs:integer` (even if it belongs to a subtype such as `xs:short`) is converted to a Java `BigInteger`. The more specialized XML Schema primitive types such as `xs:hexBinary` and `xs:duration` are passed in their native Saxon representation (a subclass of `net.sf.saxon.value.AtomicValue`).

If the expected type is one of the Saxon-specific classes (`SequenceIterator`, `ValueRepresentation`, `Item`, `Value`, `AtomicValue`, `SequenceExtent`), then the value is passed unchanged. An error occurs if the supplied value contains more than one item and the expected type does not allow this.

If the expected type implements `java.util.Collection`, Saxon attempts to convert each value in the supplied sequence to the most appropriate Java class, following the same rules as when converting a singleton to `java.lang.Object`. This process takes no account of parameterized collection types (such as `List<String>`). If the required collection type accepts an `java.util.ArrayList`, Saxon will create an `ArrayList` to hold the values; otherwise it will attempt to instantiate the required type of collection, which will only work if it is a concrete class with a zero-argument public constructor (so it will fail, for example, if the required type is `java.util.Set`). If an empty sequence is supplied as the argument value, this is converted to an empty Collection.

If the required type is an array, Saxon will attempt to create an array of the required type. This will not always succeed, for example if the array has type `X[]` where X is an interface rather than a concrete class. If it is an array of items or nodes, the nodes in the supplied sequence will be inserted into the array directly; if it is an array of a type such as integer or double, the sequence will first be atomized.

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