001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one
003     * or more contributor license agreements. See the NOTICE file
004     * distributed with this work for additional information
005     * regarding copyright ownership. The ASF licenses this file
006     * to you under the Apache License, Version 2.0 (the  "License");
007     * you may not use this file except in compliance with the License.
008     * You may obtain a copy of the License at
009     *
010     *     http://www.apache.org/licenses/LICENSE-2.0
011     *
012     * Unless required by applicable law or agreed to in writing, software
013     * distributed under the License is distributed on an "AS IS" BASIS,
014     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015     * See the License for the specific language governing permissions and
016     * limitations under the License.
017     */
018    /*
019     * $Id: Pattern.java 468650 2006-10-28 07:03:30Z minchau $
020     */
021    
022    package org.apache.xalan.xsltc.compiler;
023    
024    import org.apache.xalan.xsltc.compiler.util.ClassGenerator;
025    import org.apache.xalan.xsltc.compiler.util.MethodGenerator;
026    import org.apache.xalan.xsltc.compiler.util.Type;
027    import org.apache.xalan.xsltc.compiler.util.TypeCheckError;
028    
029    /**
030     * @author Jacek Ambroziak
031     * @author Santiago Pericas-Geertsen
032     */
033    public abstract class Pattern extends Expression {
034        /**
035         * Returns the type of a pattern, which is always a <code>NodeType</code>.
036         * A <code>NodeType</code> has a number of subtypes defined by 
037         * <code>NodeType._type</code> corresponding to each type of node.
038         */
039        public abstract Type typeCheck(SymbolTable stable) throws TypeCheckError;
040    
041        /**
042         * Translate this node into JVM bytecodes. Patterns are translated as
043         * boolean expressions with true/false lists. Before calling 
044         * <code>translate</code> on a pattern, make sure that the node being 
045         * matched is on top of the stack. After calling <code>translate</code>, 
046         * make sure to backpatch both true and false lists. True lists are the 
047         * default, in the sense that they always <em>"fall through"</em>. If this
048         * is not the intended semantics (e.g., see 
049         * {@link org.apache.xalan.xsltc.compiler.AlternativePattern#translate})
050         * then a GOTO must be appended to the instruction list after calling
051         * <code>translate</code>. 
052         */
053        public abstract void translate(ClassGenerator classGen,
054                                       MethodGenerator methodGen);
055    
056        /**
057         * Returns the priority of this pattern (section 5.5 in the XSLT spec).
058         */
059        public abstract double getPriority();
060    }