http://xmlgraphics.apache.org/fop/: Apache FOP (Formatting Objects Processor) is the world's first print formatter driven by XSL formatting objects (XSL-FO) and the world's first output independent formatter. It is a Java application that reads a formatting object (FO) tree and renders the resulting pages to a specified output. Output formats currently supported include PDF, PCL, PS, AFP, TIFF, PNG, SVG, XML (area tree representation), Print, AWT and TXT. The primary output target is PDF. (Apache Software Foundation) 
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
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/* $Id: Function.java 1330317 2012-04-25 14:48:09Z gadams $ */

package org.apache.fop.fo.expr;

import org.apache.fop.datatypes.PercentBase;
import org.apache.fop.fo.properties.Property;


Interface for managing XSL-FO Functions

/**
 * Interface for managing XSL-FO Functions
 */
public interface Function {

    
Returns:the number of required (non-optional) arguments that must be specified
in the argument list
/**
     * @return the number of required (non-optional) arguments that must be specified
     * in the argument list
     */
    int getRequiredArgsCount();

    
Returns:the number of non-required (optional) arguments that may be specified
in the argument list, which, if specified, must follow the required arguments
/**
     * @return the number of non-required (optional) arguments that may be specified
     * in the argument list, which, if specified, must follow the required arguments
     */
    int getOptionalArgsCount();

    
Params:
  • index – of optional argument
  • pi – property information instance that applies to property being evaluated
Throws:
Returns:the default property value for the optional argument at INDEX, where
INDEX is with respect to optional arguments; i.e., the first optional argument
position is index 0; if no default for a given index, then null is returned
/**
     * @param index of optional argument
     * @param pi property information instance that applies to property being evaluated
     * @return the default property value for the optional argument at INDEX, where
     * INDEX is with respect to optional arguments; i.e., the first optional argument
     * position is index 0; if no default for a given index, then null is returned
     * @throws PropertyException if index is greater than or equal to optional args count
     */
    Property getOptionalArgDefault(int index, PropertyInfo pi) throws PropertyException;

    
Determine if function allows variable arguments. If it does, then they must appear
after required and optional arguments, and all optional arguments must be specified.

Returns:true if function permits additional variable number of arguments after
required and (completely specified) optional arguments
/**
     * Determine if function allows variable arguments. If it does, then they must appear
     * after required and optional arguments, and all optional arguments must be specified.
     * @return true if function permits additional variable number of arguments after
     * required and (completely specified) optional arguments
     */
    boolean hasVariableArgs();

    
Returns:the basis for percentage calculations
/**
     * @return the basis for percentage calculations
     */
    PercentBase getPercentBase();

    
Evaluate the function

Params:
  • args – an array of Properties that should be evaluated
  • pi – property information instance that applies to property being evaluated
Throws:
Returns:the Property satisfying the function
/**
     * Evaluate the function
     * @param args an array of Properties that should be evaluated
     * @param pi property information instance that applies to property being evaluated
     * @return the Property satisfying the function
     * @throws PropertyException for problems when evaluating the function
     */
    Property eval(Property[] args, PropertyInfo pi) throws PropertyException;

}