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Java > Open Source Codes > org > eclipse > jdi > hcr > ReferenceType


1 /*******************************************************************************
2  * Copyright (c) 2000, 2005 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.jdi.hcr;
12
13
14 /**
15  * Hot code replacement extension to <code>com.sun.jdi.ReferenceType</code>.
16  */
17 public interface ReferenceType {
18     /**
19      * An HCR-eligible class file may now be loaded and reloaded at some later point(s).
20      * Methods on the stack may come from any of several versions of the same HCR-eligible class.
21      * The debugger can query any class file related object (class, method, or field) for
22      * information about the version of the class file from which it came.
23      * <p>
24      * Classes loaded by a cooperating class loader are flagged as HCR-eligible for hot code
25      * replacement.
26      * <p>
27      * Class file versions are identified by the CRC-32 of the entire class file contents.
28      * <p>
29      * The VM typically computes and remembers the CRC when it digests a class file. Note
30      * this behavior is optional; VM need not retain any CRCs.
31      * A debugger can query any class for its class CRC and eligibility:
32      * <ul>
33      * <li>The query can be made at at time.
34      * <li>This is not directed to any specific thread.
35      * <li>Threads may be running at the time; they are not stopped.
36      * <li>Other JDI-level operations may be in progress.
37      * <li>If a debugger knows only about a method or a field, it must first query its defining
38      * class first to find out what is the CRC for this method or field.
39      * </ul>
40      * All information returned does not change over the lifetime of the reference type object
41      * (replacing the class results in a new reference type object). This info can therefore be
42      * cached client-side with impunity.
43      * <p>
44      * This simple mechanism allows the IDE to detect that an object does not belong to the current
45      * class file base (debugger computes CRC of current class file and queries VM and compares to
46      * its CRC). It also allows the debugger to quickly detect whether two objects come from
47      * the same class file (debugger queries VM and compares CRCs). By checking the HCR-eligibility
48      * bit, the debugger can determine whether the class could be hot replaced in principle.
49      * <p>
50      * Returns the CRC-32 of the entire class file contents for this reference type.
51      *
52      * @see org.eclipse.jdi.hcr.VirtualMachine#classesHaveChanged
53      */
54     public int getClassFileVersion();
55     
56     /**
57      * Returns whether this reference type is eligible for hot code replacement.
58      *
59      * @see org.eclipse.jdi.hcr.ReferenceType#getClassFileVersion
60      */
61     public boolean isHCREligible();
62     
63     /**
64      * Returns whether this reference type knows its class file version.
65      * Returns false for <code>ArrayType</code>s.
66      */
67     public boolean isVersionKnown();
68 }
69
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