001 /* 002 * Licensed to the Apache Software Foundation (ASF) under one 003 * or more contributor license agreements. See the NOTICE file 004 * distributed with this work for additional information 005 * regarding copyright ownership. The ASF licenses this file 006 * to you under the Apache License, Version 2.0 (the 007 * "License"); you may not use this file except in compliance 008 * with the License. You may obtain a copy of the License at 009 * 010 * http://www.apache.org/licenses/LICENSE-2.0 011 * 012 * Unless required by applicable law or agreed to in writing, 013 * software distributed under the License is distributed on an 014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY 015 * KIND, either express or implied. See the License for the 016 * specific language governing permissions and limitations 017 * under the License. 018 */ 019 package org.apache.felix.framework.util; 020 021 import java.util.Enumeration; 022 import java.util.NoSuchElementException; 023 024 public class CompoundEnumeration implements Enumeration 025 { 026 private Enumeration[] m_enums = null; 027 private int index = 0; 028 029 public CompoundEnumeration(Enumeration[] enums) 030 { 031 m_enums = enums; 032 } 033 034 public boolean hasMoreElements() 035 { 036 // if the current enum is null that means this enum is finished 037 if (currentEnumeration() == null) 038 { 039 // No next enum 040 return false; 041 } 042 // If the current enum has more elements, lets go 043 return currentEnumeration().hasMoreElements(); 044 } 045 046 private Enumeration findNextEnumeration(boolean moveCursor) 047 { 048 return findNextEnumeration(index, moveCursor); 049 } 050 051 private Enumeration findNextEnumeration(int cursor, boolean moveCursor) 052 { 053 // next place in the array 054 int next = cursor + 1; 055 // If the cursor is still in the array 056 if (next < m_enums.length) 057 { 058 059 // If there is something in that place 060 // AND the enum is not empty 061 if (m_enums[next] != null && 062 m_enums[next].hasMoreElements()) 063 { 064 // OK 065 if (moveCursor) 066 { 067 index = next; 068 } 069 return m_enums[next]; 070 } 071 // Try next element 072 return findNextEnumeration(next, moveCursor); 073 } 074 // No more elements available 075 return null; 076 } 077 078 public Object nextElement() 079 { 080 // ask for the next element of the current enum. 081 if (currentEnumeration() != null) 082 { 083 return currentEnumeration().nextElement(); 084 } 085 086 // no more elements in this Enum 087 // We must throw a NoSuchElementException 088 throw new NoSuchElementException("No more elements"); 089 } 090 091 private Enumeration currentEnumeration() 092 { 093 if (m_enums != null) 094 { 095 if (index < m_enums.length) 096 { 097 Enumeration e = m_enums[index]; 098 if (e == null || !e.hasMoreElements()) 099 { 100 // the current enum is null or empty 101 // we probably want to switch to the next one 102 e = findNextEnumeration(true); 103 } 104 return e; 105 } 106 } 107 return null; 108 } 109 }