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Provides support for finding and displaying the differences
between hierarchically structured data.
<h2>
Package Specification</h2>
The class <tt>Differencer</tt> 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.
<p>If the input elements to the differencing engine implement the <tt>IStructureComparator</tt>
interface the engine recursively applies itself&nbsp; to the children of
the input element. Leaf elements must implement the <tt>IStreamContentAccessor</tt>
interface (see package <tt>org.eclipse.compare</tt>) so that the
differencer can perform a bytewise comparison on them.
<p>By default the differencing engine returns the result of the compare
as a tree of <tt>DiffNode</tt> objects. Every <tt>DiffNode</tt> describes
the changes among the two or three inputs.
<p>A tree of <tt>DiffNodes</tt> can be displayed in a <tt>DiffTreeViewer</tt>.
The <tt>DiffTreeViewer</tt> requires that inner nodes of the tree implement
the <tt>IDiffContainer</tt> interface and leafs the <tt>IDiffElement</tt>
interface.
<p>The typical steps to compare hierarchically structured data and to display
the differences would be to:
<blockquote>
<li>
map the input data into a tree of <tt>IStructureComparator</tt> and <tt>IStreamContentAccessor</tt>s,</li>

<li>
perform the compare operation by means of the <tt>Differencer</tt>, and</li>

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