[Chapter 16] 16.2 Transferable Interface

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| Chapter 16 Data Transfer |

## 16.2 Transferable Interface

Objects that can be placed on a clipboard must implement the `Transferable` interface. This interface defines a number of methods that let an object describe how it presents itself to clipboard readers. That sounds complex, but it isn't really; these methods let a clipboard reader find out what data flavors are available and what Java types they represent.

The significance of the `Transferable` interface is that it provides a way to get information about the object on the clipboard without knowing what the object actually is. When you read the clipboard, you don't necessarily know what kind of object is there. It might be some kind of text string, but it could just as likely be something bizarre. However, you shouldn't have to care. If you're looking for a `String`, you care only that the object exists in a `stringFlavor` representation. These methods let you ask the object what flavors it supports.

For text strings, the data transfer package provides a `StringSelection` class that implements `Transferable`. At this point, if you want to transfer other kinds of objects, you'll have to create a class that implements `Transferable` yourself. It wouldn't be unreasonable for JavaSoft to provide other "selection" classes (for example, `ImageSelection`) in the future. Methods

public abstract DataFlavor[] getTransferDataFlavors()

  The `getTransferDataFlavors()` method should return a sorted array of `DataFlavor`s that you support. The most descriptive flavor should be the first element in the array and the least descriptive, last. For example, a textual object would place `DataFlavor.plainTextFlavor` last, because it has less information than `DataFlavor.stringFlavor` (which includes information like the length of the string) and much less information than a hypothetical flavor like `DataFlavor.richTextFlavor`.

public abstract boolean isDataFlavorSupported(DataFlavor flavor)

  The `isDataFlavorSupported()` method should return `true` if the object supports the given `flavor` and `false` otherwise.

public abstract Object getTransferData(DataFlavor flavor) throws UnsupportedFlavorException, IOException

  The `getTransferData()` method is the most complicated to implement. It should return an instance of the class representing the data in the given `flavor`. If `flavor` is not supported by this object, `getTransferData()` must throw the `UnsupportedFlavorException`. However, this method must be able to return a class for each flavor the object supports (i.e., each data flavor listed by `getTransferDataFlavors()`). The method could throw an `IOException` when returning with a `Reader` as the representation class. For example, if some data flavor required you to return a `FileReader` and the file doesn't exist, this method might throw an `IOException`.

DataFlavor |  | ClipboardOwner Interface