https://github.com/google/guava/guava: Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. 
final class com.google.common.collect.Collections2$OrderedPermutationIterator<E> extends com.google.common.collect.AbstractIterator<java.util.List<E>>
  minor version: 0
  major version: 59
  flags: flags: (0x0030) ACC_FINAL, ACC_SUPER
  this_class: com.google.common.collect.Collections2$OrderedPermutationIterator
  super_class: com.google.common.collect.AbstractIterator
{
  java.util.List<E> nextPermutation;
    descriptor: Ljava/util/List;
    flags: (0x0000) 
    Signature: Ljava/util/List<TE;>;
    RuntimeVisibleTypeAnnotations: 
      FIELD
        org.checkerframework.checker.nullness.qual.Nullable()

  final java.util.Comparator<? super E> comparator;
    descriptor: Ljava/util/Comparator;
    flags: (0x0010) ACC_FINAL
    Signature: Ljava/util/Comparator<-TE;>;

  void <init>(java.util.List<E>, java.util.Comparator<? super E>);
    descriptor: (Ljava/util/List;Ljava/util/Comparator;)V
    flags: (0x0000) 
    Code:
      stack=2, locals=3, args_size=3
        start local 0 // com.google.common.collect.Collections2$OrderedPermutationIterator this
        start local 1 // java.util.List list
        start local 2 // java.util.Comparator comparator
         0: .line 515
            aload 0 /* this */
            invokespecial com.google.common.collect.AbstractIterator.<init>:()V
         1: .line 516
            aload 0 /* this */
            aload 1 /* list */
            invokestatic com.google.common.collect.Lists.newArrayList:(Ljava/lang/Iterable;)Ljava/util/ArrayList;
            putfield com.google.common.collect.Collections2$OrderedPermutationIterator.nextPermutation:Ljava/util/List;
         2: .line 517
            aload 0 /* this */
            aload 2 /* comparator */
            putfield com.google.common.collect.Collections2$OrderedPermutationIterator.comparator:Ljava/util/Comparator;
         3: .line 518
            return
        end local 2 // java.util.Comparator comparator
        end local 1 // java.util.List list
        end local 0 // com.google.common.collect.Collections2$OrderedPermutationIterator this
      LocalVariableTable:
        Start  End  Slot        Name  Signature
            0    4     0        this  Lcom/google/common/collect/Collections2$OrderedPermutationIterator<TE;>;
            0    4     1        list  Ljava/util/List<TE;>;
            0    4     2  comparator  Ljava/util/Comparator<-TE;>;
    Signature: (Ljava/util/List<TE;>;Ljava/util/Comparator<-TE;>;)V
    MethodParameters:
            Name  Flags
      list        
      comparator  

  protected java.util.List<E> computeNext();
    descriptor: ()Ljava/util/List;
    flags: (0x0004) ACC_PROTECTED
    Code:
      stack=1, locals=2, args_size=1
        start local 0 // com.google.common.collect.Collections2$OrderedPermutationIterator this
         0: .line 522
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$OrderedPermutationIterator.nextPermutation:Ljava/util/List;
            ifnonnull 2
         1: .line 523
            aload 0 /* this */
            invokevirtual com.google.common.collect.Collections2$OrderedPermutationIterator.endOfData:()Ljava/lang/Object;
            checkcast java.util.List
            areturn
         2: .line 525
      StackMap locals:
      StackMap stack:
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$OrderedPermutationIterator.nextPermutation:Ljava/util/List;
            invokestatic com.google.common.collect.ImmutableList.copyOf:(Ljava/util/Collection;)Lcom/google/common/collect/ImmutableList;
            astore 1 /* next */
        start local 1 // com.google.common.collect.ImmutableList next
         3: .line 526
            aload 0 /* this */
            invokevirtual com.google.common.collect.Collections2$OrderedPermutationIterator.calculateNextPermutation:()V
         4: .line 527
            aload 1 /* next */
            areturn
        end local 1 // com.google.common.collect.ImmutableList next
        end local 0 // com.google.common.collect.Collections2$OrderedPermutationIterator this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    5     0  this  Lcom/google/common/collect/Collections2$OrderedPermutationIterator<TE;>;
            3    5     1  next  Lcom/google/common/collect/ImmutableList<TE;>;
    Signature: ()Ljava/util/List<TE;>;

  void calculateNextPermutation();
    descriptor: ()V
    flags: (0x0000) 
    Code:
      stack=3, locals=4, args_size=1
        start local 0 // com.google.common.collect.Collections2$OrderedPermutationIterator this
         0: .line 531
            aload 0 /* this */
            invokevirtual com.google.common.collect.Collections2$OrderedPermutationIterator.findNextJ:()I
            istore 1 /* j */
        start local 1 // int j
         1: .line 532
            iload 1 /* j */
            iconst_m1
            if_icmpne 4
         2: .line 533
            aload 0 /* this */
            aconst_null
            putfield com.google.common.collect.Collections2$OrderedPermutationIterator.nextPermutation:Ljava/util/List;
         3: .line 534
            return
         4: .line 537
      StackMap locals: int
      StackMap stack:
            aload 0 /* this */
            iload 1 /* j */
            invokevirtual com.google.common.collect.Collections2$OrderedPermutationIterator.findNextL:(I)I
            istore 2 /* l */
        start local 2 // int l
         5: .line 538
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$OrderedPermutationIterator.nextPermutation:Ljava/util/List;
            iload 1 /* j */
            iload 2 /* l */
            invokestatic java.util.Collections.swap:(Ljava/util/List;II)V
         6: .line 539
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$OrderedPermutationIterator.nextPermutation:Ljava/util/List;
            invokeinterface java.util.List.size:()I
            istore 3 /* n */
        start local 3 // int n
         7: .line 540
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$OrderedPermutationIterator.nextPermutation:Ljava/util/List;
            iload 1 /* j */
            iconst_1
            iadd
            iload 3 /* n */
            invokeinterface java.util.List.subList:(II)Ljava/util/List;
            invokestatic java.util.Collections.reverse:(Ljava/util/List;)V
         8: .line 541
            return
        end local 3 // int n
        end local 2 // int l
        end local 1 // int j
        end local 0 // com.google.common.collect.Collections2$OrderedPermutationIterator this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    9     0  this  Lcom/google/common/collect/Collections2$OrderedPermutationIterator<TE;>;
            1    9     1     j  I
            5    9     2     l  I
            7    9     3     n  I

  int findNextJ();
    descriptor: ()I
    flags: (0x0000) 
    Code:
      stack=5, locals=2, args_size=1
        start local 0 // com.google.common.collect.Collections2$OrderedPermutationIterator this
         0: .line 544
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$OrderedPermutationIterator.nextPermutation:Ljava/util/List;
            invokeinterface java.util.List.size:()I
            iconst_2
            isub
            istore 1 /* k */
        start local 1 // int k
         1: goto 5
         2: .line 545
      StackMap locals: int
      StackMap stack:
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$OrderedPermutationIterator.comparator:Ljava/util/Comparator;
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$OrderedPermutationIterator.nextPermutation:Ljava/util/List;
            iload 1 /* k */
            invokeinterface java.util.List.get:(I)Ljava/lang/Object;
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$OrderedPermutationIterator.nextPermutation:Ljava/util/List;
            iload 1 /* k */
            iconst_1
            iadd
            invokeinterface java.util.List.get:(I)Ljava/lang/Object;
            invokeinterface java.util.Comparator.compare:(Ljava/lang/Object;Ljava/lang/Object;)I
            ifge 4
         3: .line 546
            iload 1 /* k */
            ireturn
         4: .line 544
      StackMap locals:
      StackMap stack:
            iinc 1 /* k */ -1
      StackMap locals:
      StackMap stack:
         5: iload 1 /* k */
            ifge 2
        end local 1 // int k
         6: .line 549
            iconst_m1
            ireturn
        end local 0 // com.google.common.collect.Collections2$OrderedPermutationIterator this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    7     0  this  Lcom/google/common/collect/Collections2$OrderedPermutationIterator<TE;>;
            1    6     1     k  I

  int findNextL(int);
    descriptor: (I)I
    flags: (0x0000) 
    Code:
      stack=4, locals=4, args_size=2
        start local 0 // com.google.common.collect.Collections2$OrderedPermutationIterator this
        start local 1 // int j
         0: .line 553
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$OrderedPermutationIterator.nextPermutation:Ljava/util/List;
            iload 1 /* j */
            invokeinterface java.util.List.get:(I)Ljava/lang/Object;
            astore 2 /* ak */
        start local 2 // java.lang.Object ak
         1: .line 554
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$OrderedPermutationIterator.nextPermutation:Ljava/util/List;
            invokeinterface java.util.List.size:()I
            iconst_1
            isub
            istore 3 /* l */
        start local 3 // int l
         2: goto 6
         3: .line 555
      StackMap locals: java.lang.Object int
      StackMap stack:
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$OrderedPermutationIterator.comparator:Ljava/util/Comparator;
            aload 2 /* ak */
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$OrderedPermutationIterator.nextPermutation:Ljava/util/List;
            iload 3 /* l */
            invokeinterface java.util.List.get:(I)Ljava/lang/Object;
            invokeinterface java.util.Comparator.compare:(Ljava/lang/Object;Ljava/lang/Object;)I
            ifge 5
         4: .line 556
            iload 3 /* l */
            ireturn
         5: .line 554
      StackMap locals:
      StackMap stack:
            iinc 3 /* l */ -1
      StackMap locals:
      StackMap stack:
         6: iload 3 /* l */
            iload 1 /* j */
            if_icmpgt 3
        end local 3 // int l
         7: .line 559
            new java.lang.AssertionError
            dup
            ldc "this statement should be unreachable"
            invokespecial java.lang.AssertionError.<init>:(Ljava/lang/Object;)V
            athrow
        end local 2 // java.lang.Object ak
        end local 1 // int j
        end local 0 // com.google.common.collect.Collections2$OrderedPermutationIterator this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    8     0  this  Lcom/google/common/collect/Collections2$OrderedPermutationIterator<TE;>;
            0    8     1     j  I
            1    8     2    ak  TE;
            2    7     3     l  I
    MethodParameters:
      Name  Flags
      j     

  protected java.lang.Object computeNext();
    descriptor: ()Ljava/lang/Object;
    flags: (0x1044) ACC_PROTECTED, ACC_BRIDGE, ACC_SYNTHETIC
    Code:
      stack=1, locals=1, args_size=1
         0: .line 1
            aload 0
            invokevirtual com.google.common.collect.Collections2$OrderedPermutationIterator.computeNext:()Ljava/util/List;
            areturn
      LocalVariableTable:
        Start  End  Slot  Name  Signature
}
Signature: <E:Ljava/lang/Object;>Lcom/google/common/collect/AbstractIterator<Ljava/util/List<TE;>;>;
SourceFile: "Collections2.java"
NestHost: com.google.common.collect.Collections2
InnerClasses:
  private final OrderedPermutationIterator = com.google.common.collect.Collections2$OrderedPermutationIterator of com.google.common.collect.Collections2