Package-level Javadoc
Author: IBM

Provides support for finding and displaying the differences between hierarchically structured data.

## Package Specification

The class Differencer is a differencing engine for hierarchically structured data. It takes two or three inputs and performs a two-way or three-way compare on them.

If the input elements to the differencing engine implement the IStructureComparator interface the engine recursively applies itself to the children of the input element. Leaf elements must implement the org.eclipse.compare.IStreamContentAccessor interface so that the differencer can perform a bytewise comparison on their contents.

One good example for this is org.eclipse.compare.ResourceNode which implements both interfaces (and more) for Eclipse workspace resources (org.eclipse.core.resources.IResource).

Another example is the DocumentRangeNode which can be used to compare hierarchical structures that are superimposed on a document, that is where nodes and leafs correspond to ranges in a document (org.eclipse.compare.contentmergeviewer.IDocumentRange).
Typically DocumentRangeNodes are created while parsing a document and they represent the semantic entities of the document (e.g. a Java class, method or field). The two subclasses JavaNode (in org.eclipse.jdt.internal.ui.compare) and PropertyNode (in org.eclipse.jdt.internal.ui.compare) are good examples for this.

By default the differencing engine returns the result of the compare operation as a tree of DiffNode objects. However, this can be changed by overriding a single method of the engine.

Every DiffNode describes the changes among the two or three inputs.

A tree of DiffNodes can be displayed in a DiffTreeViewer. The DiffTreeViewer requires that inner nodes of the tree implement the IDiffContainer interface and leafs the IDiffElement interface.

The typical steps to compare hierarchically structured data and to display the differences would be to:

- map the input data into a tree of IStructureComparator and IStreamContentAccessors,
- perform the compare operation by means of the Differencer, and
- feed the differencing result into the DiffTreeViewer.

The StructureDiffViewer is a specialized DiffTreeViewer that automates the three steps from above. It takes a single input object of type ICompareInput from which it retrieves the two or three input elements to compare. Then it uses a IStructureCreator to extract a tree of IStructureComparator and IStreamContentAccessor from them. These trees are then compared with the differencing engine and the result is displayed in the tree viewer.