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. 
class com.google.common.collect.Collections2$PermutationIterator<E> extends com.google.common.collect.AbstractIterator<java.util.List<E>>
  minor version: 0
  major version: 59
  flags: flags: (0x0020) ACC_SUPER
  this_class: com.google.common.collect.Collections2$PermutationIterator
  super_class: com.google.common.collect.AbstractIterator
{
  final java.util.List<E> list;
    descriptor: Ljava/util/List;
    flags: (0x0010) ACC_FINAL
    Signature: Ljava/util/List<TE;>;

  final int[] c;
    descriptor: [I
    flags: (0x0010) ACC_FINAL

  final int[] o;
    descriptor: [I
    flags: (0x0010) ACC_FINAL

  int j;
    descriptor: I
    flags: (0x0000) 

  void <init>(java.util.List<E>);
    descriptor: (Ljava/util/List;)V
    flags: (0x0000) 
    Code:
      stack=4, locals=3, args_size=2
        start local 0 // com.google.common.collect.Collections2$PermutationIterator this
        start local 1 // java.util.List list
         0: .line 628
            aload 0 /* this */
            invokespecial com.google.common.collect.AbstractIterator.<init>:()V
         1: .line 629
            aload 0 /* this */
            new java.util.ArrayList
            dup
            aload 1 /* list */
            invokespecial java.util.ArrayList.<init>:(Ljava/util/Collection;)V
            putfield com.google.common.collect.Collections2$PermutationIterator.list:Ljava/util/List;
         2: .line 630
            aload 1 /* list */
            invokeinterface java.util.List.size:()I
            istore 2 /* n */
        start local 2 // int n
         3: .line 631
            aload 0 /* this */
            iload 2 /* n */
            newarray 10
            putfield com.google.common.collect.Collections2$PermutationIterator.c:[I
         4: .line 632
            aload 0 /* this */
            iload 2 /* n */
            newarray 10
            putfield com.google.common.collect.Collections2$PermutationIterator.o:[I
         5: .line 633
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.c:[I
            iconst_0
            invokestatic java.util.Arrays.fill:([II)V
         6: .line 634
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.o:[I
            iconst_1
            invokestatic java.util.Arrays.fill:([II)V
         7: .line 635
            aload 0 /* this */
            ldc 2147483647
            putfield com.google.common.collect.Collections2$PermutationIterator.j:I
         8: .line 636
            return
        end local 2 // int n
        end local 1 // java.util.List list
        end local 0 // com.google.common.collect.Collections2$PermutationIterator this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    9     0  this  Lcom/google/common/collect/Collections2$PermutationIterator<TE;>;
            0    9     1  list  Ljava/util/List<TE;>;
            3    9     2     n  I
    Signature: (Ljava/util/List<TE;>;)V
    MethodParameters:
      Name  Flags
      list  

  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$PermutationIterator this
         0: .line 640
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.j:I
            ifgt 2
         1: .line 641
            aload 0 /* this */
            invokevirtual com.google.common.collect.Collections2$PermutationIterator.endOfData:()Ljava/lang/Object;
            checkcast java.util.List
            areturn
         2: .line 643
      StackMap locals:
      StackMap stack:
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.list: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 644
            aload 0 /* this */
            invokevirtual com.google.common.collect.Collections2$PermutationIterator.calculateNextPermutation:()V
         4: .line 645
            aload 1 /* next */
            areturn
        end local 1 // com.google.common.collect.ImmutableList next
        end local 0 // com.google.common.collect.Collections2$PermutationIterator this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    5     0  this  Lcom/google/common/collect/Collections2$PermutationIterator<TE;>;
            3    5     1  next  Lcom/google/common/collect/ImmutableList<TE;>;
    Signature: ()Ljava/util/List<TE;>;

  void calculateNextPermutation();
    descriptor: ()V
    flags: (0x0000) 
    Code:
      stack=4, locals=3, args_size=1
        start local 0 // com.google.common.collect.Collections2$PermutationIterator this
         0: .line 649
            aload 0 /* this */
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.list:Ljava/util/List;
            invokeinterface java.util.List.size:()I
            iconst_1
            isub
            putfield com.google.common.collect.Collections2$PermutationIterator.j:I
         1: .line 650
            iconst_0
            istore 1 /* s */
        start local 1 // int s
         2: .line 654
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.j:I
            iconst_m1
            if_icmpne 4
         3: .line 655
            return
         4: .line 659
      StackMap locals: int
      StackMap stack:
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.c:[I
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.j:I
            iaload
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.o:[I
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.j:I
            iaload
            iadd
            istore 2 /* q */
        start local 2 // int q
         5: .line 660
            iload 2 /* q */
            ifge 8
         6: .line 661
            aload 0 /* this */
            invokevirtual com.google.common.collect.Collections2$PermutationIterator.switchDirection:()V
         7: .line 662
            goto 4
         8: .line 664
      StackMap locals: int
      StackMap stack:
            iload 2 /* q */
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.j:I
            iconst_1
            iadd
            if_icmpne 14
         9: .line 665
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.j:I
            ifne 11
        10: .line 666
            goto 16
        11: .line 668
      StackMap locals:
      StackMap stack:
            iinc 1 /* s */ 1
        12: .line 669
            aload 0 /* this */
            invokevirtual com.google.common.collect.Collections2$PermutationIterator.switchDirection:()V
        13: .line 670
            goto 4
        14: .line 673
      StackMap locals:
      StackMap stack:
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.list:Ljava/util/List;
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.j:I
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.c:[I
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.j:I
            iaload
            isub
            iload 1 /* s */
            iadd
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.j:I
            iload 2 /* q */
            isub
            iload 1 /* s */
            iadd
            invokestatic java.util.Collections.swap:(Ljava/util/List;II)V
        15: .line 674
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.c:[I
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.j:I
            iload 2 /* q */
            iastore
        end local 2 // int q
        16: .line 677
      StackMap locals:
      StackMap stack:
            return
        end local 1 // int s
        end local 0 // com.google.common.collect.Collections2$PermutationIterator this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0   17     0  this  Lcom/google/common/collect/Collections2$PermutationIterator<TE;>;
            2   17     1     s  I
            5   16     2     q  I

  void switchDirection();
    descriptor: ()V
    flags: (0x0000) 
    Code:
      stack=4, locals=1, args_size=1
        start local 0 // com.google.common.collect.Collections2$PermutationIterator this
         0: .line 680
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.o:[I
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.j:I
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.o:[I
            aload 0 /* this */
            getfield com.google.common.collect.Collections2$PermutationIterator.j:I
            iaload
            ineg
            iastore
         1: .line 681
            aload 0 /* this */
            dup
            getfield com.google.common.collect.Collections2$PermutationIterator.j:I
            iconst_1
            isub
            putfield com.google.common.collect.Collections2$PermutationIterator.j:I
         2: .line 682
            return
        end local 0 // com.google.common.collect.Collections2$PermutationIterator this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    3     0  this  Lcom/google/common/collect/Collections2$PermutationIterator<TE;>;

  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$PermutationIterator.computeNext:()Ljava/util/List;
            areturn
      LocalVariableTable:
        Start  End  Slot  Name  Signature
}
Signature: <E:Ljava/lang/Object;>Lcom/google/common/collect/AbstractIterator<Ljava/util/List<TE;>;>;
SourceFile: "Collections2.java"
NestHost: com.google.common.collect.Collections2
InnerClasses:
  private PermutationIterator = com.google.common.collect.Collections2$PermutationIterator of com.google.common.collect.Collections2