https://github.com/cglib/cglib/cglib: cglib is a powerful, high performance and quality Code Generation Library, It is used to extend JAVA classes and implements interfaces at runtime. 
public class net.sf.cglib.core.CollectionUtils
  minor version: 0
  major version: 59
  flags: flags: (0x0021) ACC_PUBLIC, ACC_SUPER
  this_class: net.sf.cglib.core.CollectionUtils
  super_class: java.lang.Object
{
  private void <init>();
    descriptor: ()V
    flags: (0x0002) ACC_PRIVATE
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // net.sf.cglib.core.CollectionUtils this
         0: .line 26
            aload 0 /* this */
            invokespecial java.lang.Object.<init>:()V
            return
        end local 0 // net.sf.cglib.core.CollectionUtils this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lnet/sf/cglib/core/CollectionUtils;

  public static java.util.Map bucket(java.util.Collection, net.sf.cglib.core.Transformer);
    descriptor: (Ljava/util/Collection;Lnet/sf/cglib/core/Transformer;)Ljava/util/Map;
    flags: (0x0009) ACC_PUBLIC, ACC_STATIC
    Code:
      stack=4, locals=7, args_size=2
        start local 0 // java.util.Collection c
        start local 1 // net.sf.cglib.core.Transformer t
         0: .line 29
            new java.util.HashMap
            dup
            invokespecial java.util.HashMap.<init>:()V
            astore 2 /* buckets */
        start local 2 // java.util.Map buckets
         1: .line 30
            aload 0 /* c */
            invokeinterface java.util.Collection.iterator:()Ljava/util/Iterator;
            astore 3 /* it */
        start local 3 // java.util.Iterator it
         2: goto 9
         3: .line 31
      StackMap locals: java.util.Map java.util.Iterator
      StackMap stack:
            aload 3 /* it */
            invokeinterface java.util.Iterator.next:()Ljava/lang/Object;
            astore 4 /* value */
        start local 4 // java.lang.Object value
         4: .line 32
            aload 1 /* t */
            aload 4 /* value */
            invokeinterface net.sf.cglib.core.Transformer.transform:(Ljava/lang/Object;)Ljava/lang/Object;
            astore 5 /* key */
        start local 5 // java.lang.Object key
         5: .line 33
            aload 2 /* buckets */
            aload 5 /* key */
            invokeinterface java.util.Map.get:(Ljava/lang/Object;)Ljava/lang/Object;
            checkcast java.util.List
            astore 6 /* bucket */
        start local 6 // java.util.List bucket
         6: .line 34
            aload 6 /* bucket */
            ifnonnull 8
         7: .line 35
            aload 2 /* buckets */
            aload 5 /* key */
            new java.util.LinkedList
            dup
            invokespecial java.util.LinkedList.<init>:()V
            dup
            astore 6 /* bucket */
            invokeinterface java.util.Map.put:(Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;
            pop
         8: .line 37
      StackMap locals: java.lang.Object java.lang.Object java.util.List
      StackMap stack:
            aload 6 /* bucket */
            aload 4 /* value */
            invokeinterface java.util.List.add:(Ljava/lang/Object;)Z
            pop
        end local 6 // java.util.List bucket
        end local 5 // java.lang.Object key
        end local 4 // java.lang.Object value
         9: .line 30
      StackMap locals:
      StackMap stack:
            aload 3 /* it */
            invokeinterface java.util.Iterator.hasNext:()Z
            ifne 3
        end local 3 // java.util.Iterator it
        10: .line 39
            aload 2 /* buckets */
            areturn
        end local 2 // java.util.Map buckets
        end local 1 // net.sf.cglib.core.Transformer t
        end local 0 // java.util.Collection c
      LocalVariableTable:
        Start  End  Slot     Name  Signature
            0   11     0        c  Ljava/util/Collection;
            0   11     1        t  Lnet/sf/cglib/core/Transformer;
            1   11     2  buckets  Ljava/util/Map;
            2   10     3       it  Ljava/util/Iterator;
            4    9     4    value  Ljava/lang/Object;
            5    9     5      key  Ljava/lang/Object;
            6    9     6   bucket  Ljava/util/List;
    MethodParameters:
      Name  Flags
      c     
      t     

  public static void reverse(java.util.Map, java.util.Map);
    descriptor: (Ljava/util/Map;Ljava/util/Map;)V
    flags: (0x0009) ACC_PUBLIC, ACC_STATIC
    Code:
      stack=3, locals=4, args_size=2
        start local 0 // java.util.Map source
        start local 1 // java.util.Map target
         0: .line 43
            aload 0 /* source */
            invokeinterface java.util.Map.keySet:()Ljava/util/Set;
            invokeinterface java.util.Set.iterator:()Ljava/util/Iterator;
            astore 2 /* it */
        start local 2 // java.util.Iterator it
         1: goto 4
         2: .line 44
      StackMap locals: java.util.Iterator
      StackMap stack:
            aload 2 /* it */
            invokeinterface java.util.Iterator.next:()Ljava/lang/Object;
            astore 3 /* key */
        start local 3 // java.lang.Object key
         3: .line 45
            aload 1 /* target */
            aload 0 /* source */
            aload 3 /* key */
            invokeinterface java.util.Map.get:(Ljava/lang/Object;)Ljava/lang/Object;
            aload 3 /* key */
            invokeinterface java.util.Map.put:(Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;
            pop
        end local 3 // java.lang.Object key
         4: .line 43
      StackMap locals:
      StackMap stack:
            aload 2 /* it */
            invokeinterface java.util.Iterator.hasNext:()Z
            ifne 2
        end local 2 // java.util.Iterator it
         5: .line 47
            return
        end local 1 // java.util.Map target
        end local 0 // java.util.Map source
      LocalVariableTable:
        Start  End  Slot    Name  Signature
            0    6     0  source  Ljava/util/Map;
            0    6     1  target  Ljava/util/Map;
            1    5     2      it  Ljava/util/Iterator;
            3    4     3     key  Ljava/lang/Object;
    MethodParameters:
        Name  Flags
      source  
      target  

  public static java.util.Collection filter(java.util.Collection, net.sf.cglib.core.Predicate);
    descriptor: (Ljava/util/Collection;Lnet/sf/cglib/core/Predicate;)Ljava/util/Collection;
    flags: (0x0009) ACC_PUBLIC, ACC_STATIC
    Code:
      stack=2, locals=3, args_size=2
        start local 0 // java.util.Collection c
        start local 1 // net.sf.cglib.core.Predicate p
         0: .line 50
            aload 0 /* c */
            invokeinterface java.util.Collection.iterator:()Ljava/util/Iterator;
            astore 2 /* it */
        start local 2 // java.util.Iterator it
         1: .line 51
            goto 4
         2: .line 52
      StackMap locals: java.util.Iterator
      StackMap stack:
            aload 1 /* p */
            aload 2 /* it */
            invokeinterface java.util.Iterator.next:()Ljava/lang/Object;
            invokeinterface net.sf.cglib.core.Predicate.evaluate:(Ljava/lang/Object;)Z
            ifne 4
         3: .line 53
            aload 2 /* it */
            invokeinterface java.util.Iterator.remove:()V
         4: .line 51
      StackMap locals:
      StackMap stack:
            aload 2 /* it */
            invokeinterface java.util.Iterator.hasNext:()Z
            ifne 2
         5: .line 56
            aload 0 /* c */
            areturn
        end local 2 // java.util.Iterator it
        end local 1 // net.sf.cglib.core.Predicate p
        end local 0 // java.util.Collection c
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    6     0     c  Ljava/util/Collection;
            0    6     1     p  Lnet/sf/cglib/core/Predicate;
            1    6     2    it  Ljava/util/Iterator;
    MethodParameters:
      Name  Flags
      c     
      p     

  public static java.util.List transform(java.util.Collection, net.sf.cglib.core.Transformer);
    descriptor: (Ljava/util/Collection;Lnet/sf/cglib/core/Transformer;)Ljava/util/List;
    flags: (0x0009) ACC_PUBLIC, ACC_STATIC
    Code:
      stack=3, locals=4, args_size=2
        start local 0 // java.util.Collection c
        start local 1 // net.sf.cglib.core.Transformer t
         0: .line 60
            new java.util.ArrayList
            dup
            aload 0 /* c */
            invokeinterface java.util.Collection.size:()I
            invokespecial java.util.ArrayList.<init>:(I)V
            astore 2 /* result */
        start local 2 // java.util.List result
         1: .line 61
            aload 0 /* c */
            invokeinterface java.util.Collection.iterator:()Ljava/util/Iterator;
            astore 3 /* it */
        start local 3 // java.util.Iterator it
         2: goto 4
         3: .line 62
      StackMap locals: java.util.List java.util.Iterator
      StackMap stack:
            aload 2 /* result */
            aload 1 /* t */
            aload 3 /* it */
            invokeinterface java.util.Iterator.next:()Ljava/lang/Object;
            invokeinterface net.sf.cglib.core.Transformer.transform:(Ljava/lang/Object;)Ljava/lang/Object;
            invokeinterface java.util.List.add:(Ljava/lang/Object;)Z
            pop
         4: .line 61
      StackMap locals:
      StackMap stack:
            aload 3 /* it */
            invokeinterface java.util.Iterator.hasNext:()Z
            ifne 3
        end local 3 // java.util.Iterator it
         5: .line 64
            aload 2 /* result */
            areturn
        end local 2 // java.util.List result
        end local 1 // net.sf.cglib.core.Transformer t
        end local 0 // java.util.Collection c
      LocalVariableTable:
        Start  End  Slot    Name  Signature
            0    6     0       c  Ljava/util/Collection;
            0    6     1       t  Lnet/sf/cglib/core/Transformer;
            1    6     2  result  Ljava/util/List;
            2    5     3      it  Ljava/util/Iterator;
    MethodParameters:
      Name  Flags
      c     
      t     

  public static java.util.Map getIndexMap(java.util.List);
    descriptor: (Ljava/util/List;)Ljava/util/Map;
    flags: (0x0009) ACC_PUBLIC, ACC_STATIC
    Code:
      stack=5, locals=4, args_size=1
        start local 0 // java.util.List list
         0: .line 68
            new java.util.HashMap
            dup
            invokespecial java.util.HashMap.<init>:()V
            astore 1 /* indexes */
        start local 1 // java.util.Map indexes
         1: .line 69
            iconst_0
            istore 2 /* index */
        start local 2 // int index
         2: .line 70
            aload 0 /* list */
            invokeinterface java.util.List.iterator:()Ljava/util/Iterator;
            astore 3 /* it */
        start local 3 // java.util.Iterator it
         3: goto 5
         4: .line 71
      StackMap locals: java.util.Map int java.util.Iterator
      StackMap stack:
            aload 1 /* indexes */
            aload 3 /* it */
            invokeinterface java.util.Iterator.next:()Ljava/lang/Object;
            new java.lang.Integer
            dup
            iload 2 /* index */
            iinc 2 /* index */ 1
            invokespecial java.lang.Integer.<init>:(I)V
            invokeinterface java.util.Map.put:(Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;
            pop
         5: .line 70
      StackMap locals:
      StackMap stack:
            aload 3 /* it */
            invokeinterface java.util.Iterator.hasNext:()Z
            ifne 4
        end local 3 // java.util.Iterator it
         6: .line 73
            aload 1 /* indexes */
            areturn
        end local 2 // int index
        end local 1 // java.util.Map indexes
        end local 0 // java.util.List list
      LocalVariableTable:
        Start  End  Slot     Name  Signature
            0    7     0     list  Ljava/util/List;
            1    7     1  indexes  Ljava/util/Map;
            2    7     2    index  I
            3    6     3       it  Ljava/util/Iterator;
    MethodParameters:
      Name  Flags
      list  
}
SourceFile: "CollectionUtils.java"