Bug 32254 [Viewers] AbstractTreeViewer uses HashSet to remember expansion state
I20030216 The custom hash table should be used instead. Otherwise expansion state may be lost due to a different equals implementation of the element and the IElementComparer.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/StructuredViewer.java
*/
	public abstract void reveal(Object element);
	/**
	 * The <code>StructuredViewer</code> implementation of this method checks
	 * to ensure that the content provider is an
	 * <code>IStructuredContentProvider</code>.
	 */
	public void setContentProvider(IContentProvider provider) {
		Assert.isTrue(provider instanceof IStructuredContentProvider);
		super.setContentProvider(provider);
	}
	/*
	 * (non-Javadoc) Method declared in Viewer. This implementatation
	 * additionaly unmaps all the elements.
	 */
	public final void setInput(Object input) {
		try {
			
			unmapAllElements();
			super.setInput(input);
		} finally {
			
		}
	}
	/**
	 * The <code>StructuredViewer</code> implementation of this method does
	 * the following.
	 * <p>
	 * If the new selection differs from the current selection the hook
	 * <code>updateSelection</code> is called.