Groovy example source code file (ElvisOperatorExpression.java)

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

Java - Groovy tags/keywords

booleanexpression, booleanexpression, elvisoperatorexpression, elvisoperatorexpression, expression, expression, ternaryexpression, ternaryexpression

The Groovy ElvisOperatorExpression.java source code

/*
 * Copyright 2003-2007 the original author or authors.
 *
 * 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.
 */
package org.codehaus.groovy.ast.expr;

import org.codehaus.groovy.ast.GroovyCodeVisitor;

/**
 * Represents a short ternary expression x ?: y, which is equal 
 * to 
 * <pre>
 * def truePart = x
 * def booleanPart = truePart as boolean
 * booleanPart? truePart : y
 * </pre>
 * Even if x is no atomic expression, x will be evaluated only 
 * once. Example:
 * <pre>
 * class Foo { 
 *   def index=0 
 *   def getX(){ index++; return index }
 * }
 * def foo = new Foo()
 * def result = foo.x ?: "false case" 
 * assert foo.index == 1
 * assert result == 1 
 * <pre>
 * 
 * @author <a href="mailto:blackdrag@gmx.org">Jochen Theodorou
 * @since 1.5
 */
public class ElvisOperatorExpression extends TernaryExpression {

    public ElvisOperatorExpression(Expression base, Expression falseExpression) {
        super(getBool(base), base, falseExpression);
    }
    
    private static BooleanExpression getBool(Expression base) {
       BooleanExpression be = new BooleanExpression(base);
       be.setSourcePosition(base);
       return be;
    }

    public void visit(GroovyCodeVisitor visitor) {
        visitor.visitShortTernaryExpression(this);
    }
    
    public Expression transformExpression(ExpressionTransformer transformer) {
        Expression ret = new ElvisOperatorExpression(
                transformer.transform(getTrueExpression()),
                transformer.transform(getFalseExpression()));
        ret.setSourcePosition(this);
        return ret; 
    }
}