http://lucene.apache.org/lucene-parent/lucene-grouping: Lucene Grouping Module (The Apache Software Foundation) 
public class org.apache.lucene.search.grouping.TopGroupsCollector<T> extends org.apache.lucene.search.grouping.SecondPassGroupingCollector<T>
  minor version: 0
  major version: 59
  flags: flags: (0x0021) ACC_PUBLIC, ACC_SUPER
  this_class: org.apache.lucene.search.grouping.TopGroupsCollector
  super_class: org.apache.lucene.search.grouping.SecondPassGroupingCollector
{
  private final org.apache.lucene.search.Sort groupSort;
    descriptor: Lorg/apache/lucene/search/Sort;
    flags: (0x0012) ACC_PRIVATE, ACC_FINAL

  private final org.apache.lucene.search.Sort withinGroupSort;
    descriptor: Lorg/apache/lucene/search/Sort;
    flags: (0x0012) ACC_PRIVATE, ACC_FINAL

  private final int maxDocsPerGroup;
    descriptor: I
    flags: (0x0012) ACC_PRIVATE, ACC_FINAL

  public void <init>(org.apache.lucene.search.grouping.GroupSelector<T>, java.util.Collection<org.apache.lucene.search.grouping.SearchGroup<T>>, org.apache.lucene.search.Sort, org.apache.lucene.search.Sort, int, );
    descriptor: (Lorg/apache/lucene/search/grouping/GroupSelector;Ljava/util/Collection;Lorg/apache/lucene/search/Sort;Lorg/apache/lucene/search/Sort;IZ)V
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=8, locals=7, args_size=7
        start local 0 // org.apache.lucene.search.grouping.TopGroupsCollector this
        start local 1 // org.apache.lucene.search.grouping.GroupSelector groupSelector
        start local 2 // java.util.Collection groups
        start local 3 // org.apache.lucene.search.Sort groupSort
        start local 4 // org.apache.lucene.search.Sort withinGroupSort
        start local 5 // int maxDocsPerGroup
        start local 6 // boolean getMaxScores
         0: .line 61
            aload 0 /* this */
            aload 1 /* groupSelector */
            aload 2 /* groups */
         1: .line 62
            new org.apache.lucene.search.grouping.TopGroupsCollector$TopDocsReducer
            dup
            aload 4 /* withinGroupSort */
            iload 5 /* maxDocsPerGroup */
            iload 6 /* getMaxScores */
            invokespecial org.apache.lucene.search.grouping.TopGroupsCollector$TopDocsReducer.<init>:(Lorg/apache/lucene/search/Sort;IZ)V
            invokespecial org.apache.lucene.search.grouping.SecondPassGroupingCollector.<init>:(Lorg/apache/lucene/search/grouping/GroupSelector;Ljava/util/Collection;Lorg/apache/lucene/search/grouping/GroupReducer;)V
         2: .line 63
            aload 0 /* this */
            aload 3 /* groupSort */
            invokestatic java.util.Objects.requireNonNull:(Ljava/lang/Object;)Ljava/lang/Object;
            checkcast org.apache.lucene.search.Sort
            putfield org.apache.lucene.search.grouping.TopGroupsCollector.groupSort:Lorg/apache/lucene/search/Sort;
         3: .line 64
            aload 0 /* this */
            aload 4 /* withinGroupSort */
            invokestatic java.util.Objects.requireNonNull:(Ljava/lang/Object;)Ljava/lang/Object;
            checkcast org.apache.lucene.search.Sort
            putfield org.apache.lucene.search.grouping.TopGroupsCollector.withinGroupSort:Lorg/apache/lucene/search/Sort;
         4: .line 65
            aload 0 /* this */
            iload 5 /* maxDocsPerGroup */
            putfield org.apache.lucene.search.grouping.TopGroupsCollector.maxDocsPerGroup:I
         5: .line 67
            return
        end local 6 // boolean getMaxScores
        end local 5 // int maxDocsPerGroup
        end local 4 // org.apache.lucene.search.Sort withinGroupSort
        end local 3 // org.apache.lucene.search.Sort groupSort
        end local 2 // java.util.Collection groups
        end local 1 // org.apache.lucene.search.grouping.GroupSelector groupSelector
        end local 0 // org.apache.lucene.search.grouping.TopGroupsCollector this
      LocalVariableTable:
        Start  End  Slot             Name  Signature
            0    6     0             this  Lorg/apache/lucene/search/grouping/TopGroupsCollector<TT;>;
            0    6     1    groupSelector  Lorg/apache/lucene/search/grouping/GroupSelector<TT;>;
            0    6     2           groups  Ljava/util/Collection<Lorg/apache/lucene/search/grouping/SearchGroup<TT;>;>;
            0    6     3        groupSort  Lorg/apache/lucene/search/Sort;
            0    6     4  withinGroupSort  Lorg/apache/lucene/search/Sort;
            0    6     5  maxDocsPerGroup  I
            0    6     6     getMaxScores  Z
    Signature: (Lorg/apache/lucene/search/grouping/GroupSelector<TT;>;Ljava/util/Collection<Lorg/apache/lucene/search/grouping/SearchGroup<TT;>;>;Lorg/apache/lucene/search/Sort;Lorg/apache/lucene/search/Sort;IZ)V
    MethodParameters:
                 Name  Flags
      groupSelector    
      groups           
      groupSort        
      withinGroupSort  
      maxDocsPerGroup  
      getMaxScores     

  public org.apache.lucene.search.grouping.TopGroups<T> getTopGroups(int);
    descriptor: (I)Lorg/apache/lucene/search/grouping/TopGroups;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=10, locals=11, args_size=2
        start local 0 // org.apache.lucene.search.grouping.TopGroupsCollector this
        start local 1 // int withinGroupOffset
         0: .line 146
            aload 0 /* this */
            getfield org.apache.lucene.search.grouping.TopGroupsCollector.groups:Ljava/util/Collection;
            invokeinterface java.util.Collection.size:()I
            anewarray org.apache.lucene.search.grouping.GroupDocs
            astore 2 /* groupDocsResult */
        start local 2 // org.apache.lucene.search.grouping.GroupDocs[] groupDocsResult
         1: .line 148
            iconst_0
            istore 3 /* groupIDX */
        start local 3 // int groupIDX
         2: .line 149
            ldc 1.4E-45
            fstore 4 /* maxScore */
        start local 4 // float maxScore
         3: .line 150
            aload 0 /* this */
            getfield org.apache.lucene.search.grouping.TopGroupsCollector.groups:Ljava/util/Collection;
            invokeinterface java.util.Collection.iterator:()Ljava/util/Iterator;
            astore 6
            goto 29
      StackMap locals: org.apache.lucene.search.grouping.TopGroupsCollector int org.apache.lucene.search.grouping.GroupDocs[] int float top java.util.Iterator
      StackMap stack:
         4: aload 6
            invokeinterface java.util.Iterator.next:()Ljava/lang/Object;
            checkcast org.apache.lucene.search.grouping.SearchGroup
            astore 5 /* group */
        start local 5 // org.apache.lucene.search.grouping.SearchGroup group
         5: .line 151
            aload 0 /* this */
            getfield org.apache.lucene.search.grouping.TopGroupsCollector.groupReducer:Lorg/apache/lucene/search/grouping/GroupReducer;
            aload 5 /* group */
            getfield org.apache.lucene.search.grouping.SearchGroup.groupValue:Ljava/lang/Object;
            invokevirtual org.apache.lucene.search.grouping.GroupReducer.getCollector:(Ljava/lang/Object;)Lorg/apache/lucene/search/Collector;
            checkcast org.apache.lucene.search.grouping.TopGroupsCollector$TopDocsAndMaxScoreCollector
            astore 7 /* collector */
        start local 7 // org.apache.lucene.search.grouping.TopGroupsCollector$TopDocsAndMaxScoreCollector collector
         6: .line 154
            aload 7 /* collector */
            getfield org.apache.lucene.search.grouping.TopGroupsCollector$TopDocsAndMaxScoreCollector.sortedByScore:Z
            ifeq 16
         7: .line 155
            aload 7 /* collector */
            getfield org.apache.lucene.search.grouping.TopGroupsCollector$TopDocsAndMaxScoreCollector.topDocsCollector:Lorg/apache/lucene/search/TopDocsCollector;
            invokevirtual org.apache.lucene.search.TopDocsCollector.topDocs:()Lorg/apache/lucene/search/TopDocs;
            astore 10 /* allTopDocs */
        start local 10 // org.apache.lucene.search.TopDocs allTopDocs
         8: .line 156
            aload 10 /* allTopDocs */
            getfield org.apache.lucene.search.TopDocs.scoreDocs:[Lorg/apache/lucene/search/ScoreDoc;
            arraylength
            ifne 9
            ldc NaN
            goto 10
      StackMap locals: org.apache.lucene.search.grouping.TopGroupsCollector int org.apache.lucene.search.grouping.GroupDocs[] int float org.apache.lucene.search.grouping.SearchGroup java.util.Iterator org.apache.lucene.search.grouping.TopGroupsCollector$TopDocsAndMaxScoreCollector top top org.apache.lucene.search.TopDocs
      StackMap stack:
         9: aload 10 /* allTopDocs */
            getfield org.apache.lucene.search.TopDocs.scoreDocs:[Lorg/apache/lucene/search/ScoreDoc;
            iconst_0
            aaload
            getfield org.apache.lucene.search.ScoreDoc.score:F
      StackMap locals:
      StackMap stack: float
        10: fstore 9 /* groupMaxScore */
        start local 9 // float groupMaxScore
        11: .line 157
            aload 10 /* allTopDocs */
            getfield org.apache.lucene.search.TopDocs.scoreDocs:[Lorg/apache/lucene/search/ScoreDoc;
            arraylength
            iload 1 /* withinGroupOffset */
            if_icmpgt 14
        12: .line 158
            new org.apache.lucene.search.TopDocs
            dup
            aload 10 /* allTopDocs */
            getfield org.apache.lucene.search.TopDocs.totalHits:Lorg/apache/lucene/search/TotalHits;
            iconst_0
            anewarray org.apache.lucene.search.ScoreDoc
            invokespecial org.apache.lucene.search.TopDocs.<init>:(Lorg/apache/lucene/search/TotalHits;[Lorg/apache/lucene/search/ScoreDoc;)V
            astore 8 /* topDocs */
        start local 8 // org.apache.lucene.search.TopDocs topDocs
        13: .line 159
            goto 21
        end local 8 // org.apache.lucene.search.TopDocs topDocs
        14: .line 160
      StackMap locals: org.apache.lucene.search.grouping.TopGroupsCollector int org.apache.lucene.search.grouping.GroupDocs[] int float org.apache.lucene.search.grouping.SearchGroup java.util.Iterator org.apache.lucene.search.grouping.TopGroupsCollector$TopDocsAndMaxScoreCollector top float org.apache.lucene.search.TopDocs
      StackMap stack:
            new org.apache.lucene.search.TopDocs
            dup
            aload 10 /* allTopDocs */
            getfield org.apache.lucene.search.TopDocs.totalHits:Lorg/apache/lucene/search/TotalHits;
            aload 10 /* allTopDocs */
            getfield org.apache.lucene.search.TopDocs.scoreDocs:[Lorg/apache/lucene/search/ScoreDoc;
            iload 1 /* withinGroupOffset */
            aload 10 /* allTopDocs */
            getfield org.apache.lucene.search.TopDocs.scoreDocs:[Lorg/apache/lucene/search/ScoreDoc;
            arraylength
            iload 1 /* withinGroupOffset */
            aload 0 /* this */
            getfield org.apache.lucene.search.grouping.TopGroupsCollector.maxDocsPerGroup:I
            iadd
            invokestatic java.lang.Math.min:(II)I
            invokestatic org.apache.lucene.util.ArrayUtil.copyOfSubArray:([Ljava/lang/Object;II)[Ljava/lang/Object;
            checkcast org.apache.lucene.search.ScoreDoc[]
            invokespecial org.apache.lucene.search.TopDocs.<init>:(Lorg/apache/lucene/search/TotalHits;[Lorg/apache/lucene/search/ScoreDoc;)V
            astore 8 /* topDocs */
        end local 10 // org.apache.lucene.search.TopDocs allTopDocs
        start local 8 // org.apache.lucene.search.TopDocs topDocs
        15: .line 162
            goto 21
        end local 9 // float groupMaxScore
        end local 8 // org.apache.lucene.search.TopDocs topDocs
        16: .line 163
      StackMap locals: org.apache.lucene.search.grouping.TopGroupsCollector int org.apache.lucene.search.grouping.GroupDocs[] int float org.apache.lucene.search.grouping.SearchGroup java.util.Iterator org.apache.lucene.search.grouping.TopGroupsCollector$TopDocsAndMaxScoreCollector
      StackMap stack:
            aload 7 /* collector */
            getfield org.apache.lucene.search.grouping.TopGroupsCollector$TopDocsAndMaxScoreCollector.topDocsCollector:Lorg/apache/lucene/search/TopDocsCollector;
            iload 1 /* withinGroupOffset */
            aload 0 /* this */
            getfield org.apache.lucene.search.grouping.TopGroupsCollector.maxDocsPerGroup:I
            invokevirtual org.apache.lucene.search.TopDocsCollector.topDocs:(II)Lorg/apache/lucene/search/TopDocs;
            astore 8 /* topDocs */
        start local 8 // org.apache.lucene.search.TopDocs topDocs
        17: .line 164
            aload 7 /* collector */
            getfield org.apache.lucene.search.grouping.TopGroupsCollector$TopDocsAndMaxScoreCollector.maxScoreCollector:Lorg/apache/lucene/search/grouping/TopGroupsCollector$MaxScoreCollector;
            ifnonnull 20
        18: .line 165
            ldc NaN
            fstore 9 /* groupMaxScore */
        start local 9 // float groupMaxScore
        19: .line 166
            goto 21
        end local 9 // float groupMaxScore
        20: .line 167
      StackMap locals: org.apache.lucene.search.TopDocs
      StackMap stack:
            aload 7 /* collector */
            getfield org.apache.lucene.search.grouping.TopGroupsCollector$TopDocsAndMaxScoreCollector.maxScoreCollector:Lorg/apache/lucene/search/grouping/TopGroupsCollector$MaxScoreCollector;
            invokevirtual org.apache.lucene.search.grouping.TopGroupsCollector$MaxScoreCollector.getMaxScore:()F
            fstore 9 /* groupMaxScore */
        start local 9 // float groupMaxScore
        21: .line 171
      StackMap locals: float
      StackMap stack:
            aload 2 /* groupDocsResult */
            iload 3 /* groupIDX */
            iinc 3 /* groupIDX */ 1
            new org.apache.lucene.search.grouping.GroupDocs
            dup
            ldc NaN
        22: .line 172
            fload 9 /* groupMaxScore */
        23: .line 173
            aload 8 /* topDocs */
            getfield org.apache.lucene.search.TopDocs.totalHits:Lorg/apache/lucene/search/TotalHits;
        24: .line 174
            aload 8 /* topDocs */
            getfield org.apache.lucene.search.TopDocs.scoreDocs:[Lorg/apache/lucene/search/ScoreDoc;
        25: .line 175
            aload 5 /* group */
            getfield org.apache.lucene.search.grouping.SearchGroup.groupValue:Ljava/lang/Object;
        26: .line 176
            aload 5 /* group */
            getfield org.apache.lucene.search.grouping.SearchGroup.sortValues:[Ljava/lang/Object;
            invokespecial org.apache.lucene.search.grouping.GroupDocs.<init>:(FFLorg/apache/lucene/search/TotalHits;[Lorg/apache/lucene/search/ScoreDoc;Ljava/lang/Object;[Ljava/lang/Object;)V
        27: .line 171
            aastore
        28: .line 177
            fload 4 /* maxScore */
            fload 9 /* groupMaxScore */
            invokestatic java.lang.Math.max:(FF)F
            fstore 4 /* maxScore */
        end local 9 // float groupMaxScore
        end local 8 // org.apache.lucene.search.TopDocs topDocs
        end local 7 // org.apache.lucene.search.grouping.TopGroupsCollector$TopDocsAndMaxScoreCollector collector
        end local 5 // org.apache.lucene.search.grouping.SearchGroup group
        29: .line 150
      StackMap locals: org.apache.lucene.search.grouping.TopGroupsCollector int org.apache.lucene.search.grouping.GroupDocs[] int float top java.util.Iterator
      StackMap stack:
            aload 6
            invokeinterface java.util.Iterator.hasNext:()Z
            ifne 4
        30: .line 180
            new org.apache.lucene.search.grouping.TopGroups
            dup
            aload 0 /* this */
            getfield org.apache.lucene.search.grouping.TopGroupsCollector.groupSort:Lorg/apache/lucene/search/Sort;
            invokevirtual org.apache.lucene.search.Sort.getSort:()[Lorg/apache/lucene/search/SortField;
        31: .line 181
            aload 0 /* this */
            getfield org.apache.lucene.search.grouping.TopGroupsCollector.withinGroupSort:Lorg/apache/lucene/search/Sort;
            invokevirtual org.apache.lucene.search.Sort.getSort:()[Lorg/apache/lucene/search/SortField;
        32: .line 182
            aload 0 /* this */
            getfield org.apache.lucene.search.grouping.TopGroupsCollector.totalHitCount:I
            aload 0 /* this */
            getfield org.apache.lucene.search.grouping.TopGroupsCollector.totalGroupedHitCount:I
            aload 2 /* groupDocsResult */
        33: .line 183
            fload 4 /* maxScore */
        34: .line 180
            invokespecial org.apache.lucene.search.grouping.TopGroups.<init>:([Lorg/apache/lucene/search/SortField;[Lorg/apache/lucene/search/SortField;II[Lorg/apache/lucene/search/grouping/GroupDocs;F)V
            areturn
        end local 4 // float maxScore
        end local 3 // int groupIDX
        end local 2 // org.apache.lucene.search.grouping.GroupDocs[] groupDocsResult
        end local 1 // int withinGroupOffset
        end local 0 // org.apache.lucene.search.grouping.TopGroupsCollector this
      LocalVariableTable:
        Start  End  Slot               Name  Signature
            0   35     0               this  Lorg/apache/lucene/search/grouping/TopGroupsCollector<TT;>;
            0   35     1  withinGroupOffset  I
            1   35     2    groupDocsResult  [Lorg/apache/lucene/search/grouping/GroupDocs;
            2   35     3           groupIDX  I
            3   35     4           maxScore  F
            5   29     5              group  Lorg/apache/lucene/search/grouping/SearchGroup<TT;>;
            6   29     7          collector  Lorg/apache/lucene/search/grouping/TopGroupsCollector$TopDocsAndMaxScoreCollector;
           13   14     8            topDocs  Lorg/apache/lucene/search/TopDocs;
           15   16     8            topDocs  Lorg/apache/lucene/search/TopDocs;
           17   29     8            topDocs  Lorg/apache/lucene/search/TopDocs;
           11   16     9      groupMaxScore  F
           19   20     9      groupMaxScore  F
           21   29     9      groupMaxScore  F
            8   15    10         allTopDocs  Lorg/apache/lucene/search/TopDocs;
    Signature: (I)Lorg/apache/lucene/search/grouping/TopGroups<TT;>;
    MethodParameters:
                   Name  Flags
      withinGroupOffset  
}
Signature: <T:Ljava/lang/Object;>Lorg/apache/lucene/search/grouping/SecondPassGroupingCollector<TT;>;
SourceFile: "TopGroupsCollector.java"
NestMembers:
  org.apache.lucene.search.grouping.TopGroupsCollector$MaxScoreCollector  org.apache.lucene.search.grouping.TopGroupsCollector$TopDocsAndMaxScoreCollector  org.apache.lucene.search.grouping.TopGroupsCollector$TopDocsReducer
InnerClasses:
  private MaxScoreCollector = org.apache.lucene.search.grouping.TopGroupsCollector$MaxScoreCollector of org.apache.lucene.search.grouping.TopGroupsCollector
  private TopDocsAndMaxScoreCollector = org.apache.lucene.search.grouping.TopGroupsCollector$TopDocsAndMaxScoreCollector of org.apache.lucene.search.grouping.TopGroupsCollector
  private TopDocsReducer = org.apache.lucene.search.grouping.TopGroupsCollector$TopDocsReducer of org.apache.lucene.search.grouping.TopGroupsCollector