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Java example source code file (LogicalExpr.java)

This example Java source code file (LogicalExpr.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

castexpr, expression, goto, instructionhandle, logicalexpr, methodgenerator, methodtype, notcall, object, ops, string, type, typecheckerror

The LogicalExpr.java Java example source code

/*
 * reserved comment block
 * DO NOT REMOVE OR ALTER!
 */
/*
 * 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: LogicalExpr.java,v 1.2.4.1 2005/09/01 16:03:31 pvedula Exp $
 */

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

import com.sun.org.apache.bcel.internal.generic.GOTO;
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.ClassGenerator;
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.Type;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.TypeCheckError;

/**
 * @author Jacek Ambroziak
 * @author Santiago Pericas-Geertsen
 * @author Morten Jorgensen
 */
final class LogicalExpr extends Expression {

    public static final int OR  = 0;
    public static final int AND = 1;

    private final int  _op;     // operator
    private Expression _left;   // first operand
    private Expression _right;  // second operand

    private static final String[] Ops = { "or", "and" };

    /**
     * Creates a new logical expression - either OR or AND. Note that the
     * left- and right-hand side expressions can also be logical expressions,
     * thus creating logical trees representing structures such as
     * (a and (b or c) and d), etc...
     */
    public LogicalExpr(int op, Expression left, Expression right) {
        _op = op;
        (_left = left).setParent(this);
        (_right = right).setParent(this);
    }

    /**
     * Returns true if this expressions contains a call to position(). This is
     * needed for context changes in node steps containing multiple predicates.
     */
    public boolean hasPositionCall() {
        return (_left.hasPositionCall() || _right.hasPositionCall());
    }

    /**
     * Returns true if this expressions contains a call to last()
     */
    public boolean hasLastCall() {
            return (_left.hasLastCall() || _right.hasLastCall());
    }

    /**
     * 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() {
        final Object leftb = _left.evaluateAtCompileTime();
        final Object rightb = _right.evaluateAtCompileTime();

        // Return null if we can't evaluate at compile time
        if (leftb == null || rightb == null) {
            return null;
        }

        if (_op == AND) {
            return (leftb == Boolean.TRUE && rightb == Boolean.TRUE) ?
                Boolean.TRUE : Boolean.FALSE;
        }
        else {
            return (leftb == Boolean.TRUE || rightb == Boolean.TRUE) ?
                Boolean.TRUE : Boolean.FALSE;
        }
    }

    /**
     * Returns this logical expression's operator - OR or AND represented
     * by 0 and 1 respectively.
     */
    public int getOp() {
        return(_op);
    }

    /**
     * Override the SyntaxTreeNode.setParser() method to make sure that the
     * parser is set for sub-expressions
     */
    public void setParser(Parser parser) {
        super.setParser(parser);
        _left.setParser(parser);
        _right.setParser(parser);
    }

    /**
     * Returns a string describing this expression
     */
    public String toString() {
        return Ops[_op] + '(' + _left + ", " + _right + ')';
    }

    /**
     * Type-check this expression, and possibly child expressions.
     */
    public Type typeCheck(SymbolTable stable) throws TypeCheckError {
        // Get the left and right operand types
        Type tleft = _left.typeCheck(stable);
        Type tright = _right.typeCheck(stable);

        // Check if the operator supports the two operand types
        MethodType wantType = new MethodType(Type.Void, tleft, tright);
        MethodType haveType = lookupPrimop(stable, Ops[_op], wantType);

        // Yes, the operation is supported
        if (haveType != null) {
            // Check if left-hand side operand must be type casted
            Type arg1 = (Type)haveType.argsType().elementAt(0);
            if (!arg1.identicalTo(tleft))
                _left = new CastExpr(_left, arg1);
            // Check if right-hand side operand must be type casted
            Type arg2 = (Type) haveType.argsType().elementAt(1);
            if (!arg2.identicalTo(tright))
                _right = new CastExpr(_right, arg1);
            // Return the result type for the operator we will use
            return _type = haveType.resultType();
        }
        throw new TypeCheckError(this);
    }

    /**
     * Compile the expression - leave boolean expression on stack
     */
    public void translate(ClassGenerator classGen, MethodGenerator methodGen) {
        translateDesynthesized(classGen, methodGen);
        synthesize(classGen, methodGen);
    }

    /**
     * Compile expression and update true/false-lists
     */
    public void translateDesynthesized(ClassGenerator classGen,
                                       MethodGenerator methodGen) {

        final InstructionList il = methodGen.getInstructionList();
        final SyntaxTreeNode parent = getParent();

        // Compile AND-expression
        if (_op == AND) {

            // Translate left hand side - must be true
            _left.translateDesynthesized(classGen, methodGen);

            // Need this for chaining any OR-expression children
            InstructionHandle middle = il.append(NOP);

            // Translate left right side - must be true
            _right.translateDesynthesized(classGen, methodGen);

            // Need this for chaining any OR-expression children
            InstructionHandle after = il.append(NOP);

            // Append child expression false-lists to our false-list
            _falseList.append(_right._falseList.append(_left._falseList));

            // Special case for OR-expression as a left child of AND.
            // The true-list of OR must point to second clause of AND.
            if ((_left instanceof LogicalExpr) &&
                (((LogicalExpr)_left).getOp() == OR)) {
                _left.backPatchTrueList(middle);
            }
            else if (_left instanceof NotCall) {
                _left.backPatchTrueList(middle);
            }
            else {
                _trueList.append(_left._trueList);
            }

            // Special case for OR-expression as a right child of AND
            // The true-list of OR must point to true-list of AND.
            if ((_right instanceof LogicalExpr) &&
                (((LogicalExpr)_right).getOp() == OR)) {
                _right.backPatchTrueList(after);
            }
            else if (_right instanceof NotCall) {
                _right.backPatchTrueList(after);
            }
            else {
                _trueList.append(_right._trueList);
            }
        }
        // Compile OR-expression
        else {
            // Translate left-hand side expression and produce true/false list
            _left.translateDesynthesized(classGen, methodGen);

            // This GOTO is used to skip over the code for the last test
            // in the case where the the first test succeeds
            InstructionHandle ih = il.append(new GOTO(null));

            // Translate right-hand side expression and produce true/false list
            _right.translateDesynthesized(classGen, methodGen);

            _left._trueList.backPatch(ih);
            _left._falseList.backPatch(ih.getNext());

            _falseList.append(_right._falseList);
            _trueList.add(ih).append(_right._trueList);
        }
    }
}

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