[20] | 1 | /* |
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| 2 | * Cloud9: A MapReduce Library for Hadoop |
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| 3 | * |
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| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); you |
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| 5 | * may not use this file except in compliance with the License. You may |
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| 6 | * obtain a copy of the License at |
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| 7 | * |
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| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
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| 9 | * |
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| 10 | * Unless required by applicable law or agreed to in writing, software |
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| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
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| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or |
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| 13 | * implied. See the License for the specific language governing |
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| 14 | * permissions and limitations under the License. |
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| 15 | */ |
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| 16 | |
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| 17 | package tw.org.nchc.tuple; |
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| 18 | |
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| 19 | import java.io.DataInput; |
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| 20 | import java.io.DataOutput; |
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| 21 | import java.io.IOException; |
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| 22 | import java.util.ArrayList; |
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| 23 | import org.apache.hadoop.io.WritableComparable; |
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| 24 | |
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| 25 | /** |
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| 26 | * <p> |
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| 27 | * Class that represents an array list in Hadoop's data type system. It extends ArrayList class, |
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| 28 | * hence supports all services provided by ArrayList. |
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| 29 | * Elements in the list must be homogeneous and must implement Hadoop's Writable interface. |
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| 30 | * This class, combined with {@link Tuple}, allows the user to |
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| 31 | * define arbitrarily complex data structures. |
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| 32 | * </p> |
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| 33 | * |
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| 34 | * @see Tuple |
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| 35 | * @param <E> |
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| 36 | * type of list element |
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| 37 | */ |
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| 38 | |
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| 39 | public class ArrayListWritableComparable<E extends WritableComparable> extends ArrayList<E> implements WritableComparable{ |
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| 40 | |
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| 41 | private static final long serialVersionUID = 1L; |
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| 42 | |
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| 43 | /** |
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| 44 | * Creates an ArrayListWritable object. |
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| 45 | */ |
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| 46 | public ArrayListWritableComparable() { |
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| 47 | super(); |
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| 48 | } |
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| 49 | |
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| 50 | /** |
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| 51 | * Creates an ArrayListWritableComparable object from a regular ArrayList. |
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| 52 | */ |
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| 53 | public ArrayListWritableComparable(ArrayList<E> array) { |
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| 54 | super(array); |
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| 55 | } |
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| 56 | |
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| 57 | |
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| 58 | |
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| 59 | /** |
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| 60 | * Deserializes the array. |
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| 61 | * |
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| 62 | * @param in |
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| 63 | * source for raw byte representation |
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| 64 | */ |
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| 65 | @SuppressWarnings("unchecked") |
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| 66 | public void readFields(DataInput in) throws IOException { |
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| 67 | |
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| 68 | this.clear(); |
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| 69 | |
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| 70 | int numFields = in.readInt(); |
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| 71 | if(numFields==0) return; |
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| 72 | String className = in.readUTF(); |
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| 73 | E obj; |
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| 74 | try { |
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| 75 | Class c = Class.forName(className); |
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| 76 | for (int i = 0; i < numFields; i++) { |
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| 77 | obj = (E) c.newInstance(); |
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| 78 | obj.readFields(in); |
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| 79 | this.add(obj); |
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| 80 | } |
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| 81 | |
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| 82 | } catch (ClassNotFoundException e) { |
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| 83 | e.printStackTrace(); |
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| 84 | } catch (IllegalAccessException e) { |
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| 85 | e.printStackTrace(); |
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| 86 | } catch (InstantiationException e) { |
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| 87 | e.printStackTrace(); |
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| 88 | } |
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| 89 | } |
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| 90 | |
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| 91 | /** |
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| 92 | * Serializes this Tuple. |
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| 93 | * |
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| 94 | * @param out |
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| 95 | * where to write the raw byte representation |
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| 96 | */ |
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| 97 | public void write(DataOutput out) throws IOException { |
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| 98 | out.writeInt(this.size()); |
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| 99 | if(size()==0) return; |
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| 100 | E obj=get(0); |
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| 101 | |
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| 102 | out.writeUTF(obj.getClass().getCanonicalName()); |
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| 103 | |
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| 104 | for (int i = 0; i < size(); i++) { |
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| 105 | obj = get(i); |
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| 106 | if (obj == null) { |
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| 107 | throw new IOException("Cannot serialize null fields!"); |
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| 108 | } |
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| 109 | obj.write(out); |
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| 110 | } |
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| 111 | } |
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| 112 | |
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| 113 | /** |
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| 114 | * <p> |
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| 115 | * Defines a natural sort order for the ListWritable class. Following |
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| 116 | * standard convention, this method returns a value less than zero, a value |
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| 117 | * greater than zero, or zero if this ListWritable should be sorted before, |
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| 118 | * sorted after, or is equal to <code>obj</code>. The sort order is |
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| 119 | * defined as follows: |
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| 120 | * </p> |
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| 121 | * |
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| 122 | * <ul> |
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| 123 | * <li>Each element in the list is compared sequentially from first to |
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| 124 | * last.</li> |
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| 125 | * <li>Lists are sorted with respect to the natural order of the current |
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| 126 | * list element under consideration, by calling its <code>compareTo</code> |
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| 127 | * method.</li> |
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| 128 | * <li>If the current list elements are equal, the next set of elements are |
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| 129 | * considered.</li> |
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| 130 | * <li>If all compared elements are equal, but lists are different lengths, |
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| 131 | * the shorter list is sorted first.</li> |
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| 132 | * <li>If all list elements are equal and the lists are equal in length, |
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| 133 | * then the lists are considered equal</li> |
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| 134 | * </ul> |
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| 135 | * |
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| 136 | * @return a value less than zero, a value greater than zero, or zero if |
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| 137 | * this Tuple should be sorted before, sorted after, or is equal to |
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| 138 | * <code>obj</code>. |
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| 139 | */ |
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| 140 | public int compareTo(Object obj) { |
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| 141 | ArrayListWritableComparable<?> that = (ArrayListWritableComparable<?>) obj; |
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| 142 | |
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| 143 | // iterate through the fields |
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| 144 | for (int i = 0; i < this.size(); i++) { |
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| 145 | // sort shorter list first |
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| 146 | if (i >= that.size()) |
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| 147 | return 1; |
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| 148 | |
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| 149 | @SuppressWarnings("unchecked") |
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| 150 | Comparable<Object> thisField = this.get(i); |
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| 151 | @SuppressWarnings("unchecked") |
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| 152 | Comparable<Object> thatField = that.get(i); |
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| 153 | |
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| 154 | if (thisField.equals(thatField)) { |
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| 155 | // if we're down to the last field, sort shorter list first |
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| 156 | if (i == this.size() - 1) { |
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| 157 | if (this.size() > that.size()) |
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| 158 | return 1; |
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| 159 | |
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| 160 | if (this.size() < that.size()) |
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| 161 | return -1; |
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| 162 | } |
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| 163 | // otherwise, move to next field |
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| 164 | } else { |
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| 165 | return thisField.compareTo(thatField); |
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| 166 | } |
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| 167 | } |
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| 168 | |
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| 169 | return 0; |
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| 170 | } |
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| 171 | |
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| 172 | |
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| 173 | /** |
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| 174 | * Generates human-readable String representation of this ArrayList. |
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| 175 | * |
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| 176 | * @return human-readable String representation of this ArrayList |
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| 177 | */ |
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| 178 | public String toString() { |
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| 179 | StringBuffer sb = new StringBuffer(); |
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| 180 | sb.append("["); |
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| 181 | for (int i = 0; i < this.size(); i++){ |
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| 182 | if (i != 0) |
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| 183 | sb.append(", "); |
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| 184 | sb.append(this.get(i)); |
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| 185 | } |
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| 186 | sb.append("]"); |
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| 187 | |
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| 188 | return sb.toString(); |
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| 189 | } |
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| 190 | |
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| 191 | } |
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