| /******************************************************************************* |
| * Copyright (c) 2000, 2004 International Business Machines Corp. and others. |
| * All rights reserved. This program and the accompanying materials |
| * are made available under the terms of the Common Public License v0.5 |
| * which accompanies this distribution, and is available at |
| * http://www.eclipse.org/legal/cpl-v05.html |
| * |
| * Contributors: |
| * IBM Corporation - initial API and implementation |
| ******************************************************************************/ |
| package org.eclipse.core.expressions; |
| |
| import org.eclipse.core.runtime.CoreException; |
| |
| /** |
| * Abstract base class for all expressions provided by the common |
| * expression language. |
| * <p> |
| * An expression is evaluated by calling {@link #evaluate(IVariablePool)}. |
| * </p> |
| * <p> |
| * This class may be subclassed to provide specific expressions. |
| * </p> |
| * |
| * @since 3.0 |
| */ |
| public abstract class Expression { |
| |
| /** |
| * Name of the value attribute of an expression (value is |
| * <code>value</code>). |
| */ |
| protected static final String ATT_VALUE= "value"; //$NON-NLS-1$ |
| |
| /** |
| * The expression corresponding to {@link EvaluationResult#TRUE}. |
| */ |
| public static final Expression TRUE= new Expression() { |
| public EvaluationResult evaluate(IEvaluationContext context) { |
| return EvaluationResult.TRUE; |
| } |
| }; |
| |
| /** |
| * The expression corresponding to {@link EvaluationResult#FALSE}. |
| */ |
| public static final Expression FALSE= new Expression() { |
| public EvaluationResult evaluate(IEvaluationContext context) { |
| return EvaluationResult.FALSE; |
| } |
| }; |
| |
| /** |
| * Evaluates this expression. |
| * |
| * @param context a evaluation context providing information like variable, |
| * name spaces, etc. necessary to evaluate this expression |
| * |
| * @return the result of the expression evaluation |
| * |
| * @throws CoreException if the evaluation failed. The concrete reason is |
| * defined by the subclass implementing this method |
| */ |
| public abstract EvaluationResult evaluate(IEvaluationContext context) throws CoreException; |
| |
| } |