ObjectAddress


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.core.internal.indexing;
12  
13  public class ObjectAddress implements Insertable {
14  
15      public static final int Size = 4;
16      public static ObjectAddress Null = new ObjectAddress(0, 0);
17      private static final int PageNumberOffset = 0;
18      private static final int ObjectNumberOffset = 3;
19      private int pageNumber;
20      private int objectNumber;
21  
22      /**
23       * Constructor for an address from a four byte field.
24       */
25      public ObjectAddress(byte[] b) throws IllegalArgumentException   {
26          if (b.length != Size)
27              throw new IllegalArgumentException  ();
28          Buffer buf = new Buffer(b);
29          pageNumber = buf.getUInt(PageNumberOffset, 3);
30          objectNumber = buf.getUInt(ObjectNumberOffset, 1);
31      }
32  
33      /**
34       * Constructs an address from its constituent page and object numbers.
35       */
36      public ObjectAddress(int pageNumber, int objectNumber) throws IllegalArgumentException   {
37          if (pageNumber == 0 && objectNumber == 0) {
38              this.pageNumber = 0;
39              this.objectNumber = 0;
40              return;
41          }
42          if (pageNumber < 0 || pageNumber > 0xFFFFFF)
43              throw new IllegalArgumentException  ();
44          if (pageNumber % ObjectStorePage.SIZE == 0)
45              throw new IllegalArgumentException  ();
46          if (objectNumber < 0 || objectNumber > 0xFF)
47              throw new IllegalArgumentException  ();
48          this.pageNumber = pageNumber;
49          this.objectNumber = objectNumber;
50      }
51  
52      /**
53       * Returns true if and only if the addresses are equal.
54       */
55      public boolean equals(Object   anObject) {
56          if (!(anObject instanceof ObjectAddress))
57              return false;
58          ObjectAddress address = (ObjectAddress) anObject;
59          if (pageNumber != address.pageNumber)
60              return false;
61          if (objectNumber != address.objectNumber)
62              return false;
63          return true;
64      }
65  
66      /**
67       * Returns the object number from the address.
68       */
69      public int getObjectNumber() {
70          return objectNumber;
71      }
72  
73      /** 
74       * Returns the page number from the address.
75       */
76      public int getPageNumber() {
77          return pageNumber;
78      }
79  
80      /**
81       * Returns an int representing the hash code for the address.
82       */
83      public int hashCode() {
84          return (pageNumber << 8) | objectNumber;
85      }
86  
87      /**
88       * Tests the address for the null address value.
89       */
90      public boolean isNull() {
91          return (pageNumber == 0 && objectNumber == 0);
92      }
93  
94      /**
95       * Returns a byte array form of the address.
96       */
97      public byte[] toByteArray() {
98          Buffer buf = new Buffer(Size);
99          buf.put(PageNumberOffset, 3, pageNumber);
100         buf.put(ObjectNumberOffset, 1, objectNumber);
101         return buf.get();
102     }
103 }
104
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