IEvaluationContext


1   /*******************************************************************************
2    * Copyright (c) 2000, 2006 IBM Corporation and others.
3    * All rights reserved. This program and the accompanying materials
4    * are made available under the terms of the Eclipse Public License v1.0
5    * which accompanies this distribution, and is available at
6    * http://www.eclipse.org/legal/epl-v10.html
7    *
8    * Contributors:
9    *     IBM Corporation - initial API and implementation
10   *******************************************************************************/
11  package org.eclipse.core.expressions;
12  
13  import org.eclipse.core.runtime.CoreException;
14  
15  /**
16   * An evaluation context is used to manage a set of objects needed during
17   * XML expression evaluation. A context has a parent context, can manage
18   * a set of named variables and has a default variable. The default variable 
19   * is used during XML expression evaluation if no explicit variable is 
20   * referenced.
21   * <p>
22   * This interface is not intended to be implemented by clients. Clients
23   * are allowed to instantiate <code>EvaluationContext</code>. 
24   * </p>
25   * 
26   * @since 3.0
27   */
28  public interface IEvaluationContext {
29  
30      /**
31       * Returns the parent context or <code>null</code> if 
32       * this is the root of the evaluation context hierarchy.
33       * 
34       * @return the parent evaluation context or <code>null</code>
35       */
36      public IEvaluationContext getParent();
37      
38      /**
39       * Returns the root evaluation context.
40       * 
41       * @return the root evaluation context
42       */
43      public IEvaluationContext getRoot();
44      
45      /**
46       * Specifies whether this evaluation context allows activation
47       * of plug-ins for testers used in the expression tree. To actual
48       * trigger the plug-in loading this flag has to be set to <code>
49       * true</code> and the actual test expression must have the
50       * attribute <code>forcePluginActivation</code> set to <code>
51       * true</code> as well.
52       * 
53       * @param value whether this evaluation context allows plug-in activation
54       * @since 3.2
55       */
56      public void setAllowPluginActivation(boolean value);
57      
58      /**
59       * Returns whether this evaluation context supports plug-in 
60       * activation. If not set via {@link #setAllowPluginActivation(boolean)}
61       * the parent value is returned. If no parent is set <code>false</code>
62       * is returned.
63       * 
64       * @return whether plug-in activation is supported or not
65       * @since 3.2
66       */
67      public boolean getAllowPluginActivation();
68      
69      /**
70       * Returns the default variable.
71       * 
72       * @return the default variable or <code>null</code> if
73       *  no default variable is managed.
74       */
75      public Object   getDefaultVariable();
76      
77      /**
78       * Adds a new named variable to this context. If a variable
79       * with the name already exists the new one overrides the
80       * existing one.
81       * 
82       * @param name the variable's name
83       * @param value the variable's value
84       */
85      public void addVariable(String   name, Object   value);
86      
87      /**
88       * Removes the variable managed under the given name
89       * from this evaluation context.
90       * 
91       * @param name the variable's name
92       * @return the currently stored value or <code>null</code> if
93       *  the variable doesn't exist
94       */
95      public Object   removeVariable(String   name);
96      
97      /**
98       * Returns the variable managed under the given name.
99       * 
100      * @param name the variable's name
101      * @return the variable's value or <code>null</code> if the content
102      *  doesn't manage a variable with the given name 
103      */
104     public Object   getVariable(String   name);
105     
106     /**
107      * Resolves a variable for the given name and arguments. This
108      * method can be used to dynamically resolve variable such as
109      * plug-in descriptors, resources, etc. The method is used
110      * by the <code>resolve</code> expression.
111      * 
112      * @param name the variable to resolve
113      * @param args an object array of arguments used to resolve the
114      *  variable
115      * @return the variable's value or <code>null</code> if no variable
116      *  can be resolved for the given name and arguments
117      * @exception CoreException if an errors occurs while resolving
118      *  the variable
119      */
120     public Object   resolveVariable(String   name, Object  [] args) throws CoreException;
121 }
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