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Prefuse is a set of software tools for creating rich interactive data visualizations in the Java programming language.

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package prefuse.data.expression;

/**
 * Visitor interface for objects that visit each sub-expression of an
 * Expression instance, performing some computation or data collection.
 * 
 * @author jeffrey heer
 */
public interface ExpressionVisitor {

    /**
     * Callback made when visiting a particular expression.
     * @param expr the expression currently being visited.
     */
    public void visitExpression(Expression expr);
    
    /**
     * Callback to signal that the visitor has just descended
     * a level in the Expression tree.
     */
    public void down();
    
    /**
     * Callback to signal that the visitor has just ascended
     * a level in the Expression tree.
     */
    public void up();
    
} // end of interface ExpressionVisitor