expression.java

java1.6众多例子参考

/*
 * Copyright 2001-2004 The Apache Software Foundation.
 *
 * Licensed 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
 * limitations under the License.
 */
/*
 * $Id: Expression.java,v 1.2.4.1 2005/09/01 14:17:51 pvedula Exp $
 */

package com.sun.org.apache.xalan.internal.xsltc.compiler;

import java.util.Vector;

import com.sun.org.apache.bcel.internal.generic.BranchHandle;
import com.sun.org.apache.bcel.internal.generic.ConstantPoolGen;
import com.sun.org.apache.bcel.internal.generic.GOTO_W;
import com.sun.org.apache.bcel.internal.generic.IFEQ;
import com.sun.org.apache.bcel.internal.generic.InstructionHandle;
import com.sun.org.apache.bcel.internal.generic.InstructionList;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.BooleanType;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.ClassGenerator;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.ErrorMsg;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.MethodGenerator;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.MethodType;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.NodeSetType;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.Type;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.TypeCheckError;

/**
 * @author Jacek Ambroziak
 * @author Santiago Pericas-Geertsen
 * @author Morten Jorgensen
 * @author Erwin Bolwidt <[e-mail]>
 */
abstract class Expression extends SyntaxTreeNode {
    /**
     * The type of this expression. It is set after calling 
     * <code>typeCheck()</code>.
     */
    protected Type _type;

    /**
     * Instruction handles that comprise the true list.
     */
    protected FlowList _trueList = new FlowList();

    /**
     * Instruction handles that comprise the false list.
     */
    protected FlowList _falseList = new FlowList();

    public Type getType() {
	return _type;
    }

    public abstract String toString();

    public boolean hasPositionCall() {
	return false;		// default should be 'false' for StepPattern
    }

    public boolean hasLastCall() {
	return false;
    }
		
    /**
     * Returns an object representing the compile-time evaluation 
     * of an expression. We are only using this for function-available
     * and element-available at this time.
     */
    public Object evaluateAtCompileTime() {
	return null;
    }

    /**
     * Type check all the children of this node.
     */
    public Type typeCheck(SymbolTable stable) throws TypeCheckError {
	return typeCheckContents(stable);
    }

    /**
     * Translate this node into JVM bytecodes.
     */
    public void translate(ClassGenerator classGen, MethodGenerator methodGen) {
	ErrorMsg msg = new ErrorMsg(ErrorMsg.NOT_IMPLEMENTED_ERR,
				    getClass(), this);
	getParser().reportError(FATAL, msg);
    }
	
    /**
     * Translate this node into a fresh instruction list.
     * The original instruction list is saved and restored.
     */
    public final InstructionList compile(ClassGenerator classGen,
					 MethodGenerator methodGen) {
	final InstructionList result, save = methodGen.getInstructionList();
	methodGen.setInstructionList(result = new InstructionList());
	translate(classGen, methodGen);
	methodGen.setInstructionList(save);
	return result;
    }

    /**
     * Redefined by expressions of type boolean that use flow lists.
     */
    public void translateDesynthesized(ClassGenerator classGen,
				       MethodGenerator methodGen) {
	translate(classGen, methodGen);
	if (_type instanceof BooleanType) {
	    desynthesize(classGen, methodGen);
	}
    }

    /**
     * If this expression is of type node-set and it is not a variable
     * reference, then call setStartNode() passing the context node.
     */
    public void startIterator(ClassGenerator classGen,
				   MethodGenerator methodGen) {
	// Ignore if type is not node-set
	if (_type instanceof NodeSetType == false) {
	    return;
	}

	// setStartNode() should not be called if expr is a variable ref
	Expression expr = this;
	if (expr instanceof CastExpr) {
	    expr = ((CastExpr) expr).getExpr();
	}
	if (expr instanceof VariableRefBase == false) {
	    final InstructionList il = methodGen.getInstructionList();
	    il.append(methodGen.loadContextNode());
	    il.append(methodGen.setStartNode());
	}
    }

    /**
     * Synthesize a boolean expression, i.e., either push a 0 or 1 onto the 
     * operand stack for the next statement to succeed. Returns the handle
     * of the instruction to be backpatched.
     */
    public void synthesize(ClassGenerator classGen, MethodGenerator methodGen) {
	final ConstantPoolGen cpg = classGen.getConstantPool();
	final InstructionList il = methodGen.getInstructionList();
	_trueList.backPatch(il.append(ICONST_1));
	final BranchHandle truec = il.append(new GOTO_W(null));
	_falseList.backPatch(il.append(ICONST_0));
	truec.setTarget(il.append(NOP));
    }

    public void desynthesize(ClassGenerator classGen,
			     MethodGenerator methodGen) {
	final InstructionList il = methodGen.getInstructionList();
	_falseList.add(il.append(new IFEQ(null)));
    }

    public FlowList getFalseList() {
	return _falseList;
    }

    public FlowList getTrueList() {
	return _trueList;
    }

    public void backPatchFalseList(InstructionHandle ih) {
	_falseList.backPatch(ih);
    }

    public void backPatchTrueList(InstructionHandle ih) {
	_trueList.backPatch(ih);
    }

    /**
     * Search for a primop in the symbol table that matches the method type 
     * <code>ctype</code>. Two methods match if they have the same arity.
     * If a primop is overloaded then the "closest match" is returned. The
     * first entry in the vector of primops that has the right arity is 
     * considered to be the default one.
     */
    public MethodType lookupPrimop(SymbolTable stable, String op,
				   MethodType ctype) {
	MethodType result = null;
	final Vector primop = stable.lookupPrimop(op);
	if (primop != null) {
	    final int n = primop.size();
	    int minDistance = Integer.MAX_VALUE;
	    for (int i = 0; i < n; i++) {
		final MethodType ptype = (MethodType) primop.elementAt(i);
		// Skip if different arity
		if (ptype.argsCount() != ctype.argsCount()) {
		    continue;
		}
				
		// The first method with the right arity is the default
		if (result == null) {
		    result = ptype;		// default method
		}

		// Check if better than last one found
		final int distance = ctype.distanceTo(ptype);
		if (distance < minDistance) {
		    minDistance = distance;
		    result = ptype;
		}
	    }		
	}	
	return result;
    }	
}