com.google.common.collect

## Class Lists

- java.lang.Object
- - com.google.common.collect.Lists

-     @GwtCompatible(emulated=true)
      public final class Lists
      extends java.lang.Object

  Static utility methods pertaining to `List` instances. Also see this class's counterparts `Sets`, `Maps` and `Queues`.

  See the Guava User Guide article on `Lists`.

  Since:
    2.0

- - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `static <E> java.util.List<E>` | `asList(E first, E[] rest)` Returns an unmodifiable list containing the specified first element and backed by the specified array of additional elements.
    `static <E> java.util.List<E>` | `asList(E first, E second, E[] rest)` Returns an unmodifiable list containing the specified first and second element, and backed by the specified array of additional elements.
    `static <B> java.util.List<java.util.List<B>>` | `cartesianProduct(java.util.List<? extends B>... lists)` Returns every possible list that can be formed by choosing one element from each of the given lists in order; the "n-ary Cartesian product" of the lists.
    `static <B> java.util.List<java.util.List<B>>` | `cartesianProduct(java.util.List<? extends java.util.List<? extends B>> lists)` Returns every possible list that can be formed by choosing one element from each of the given lists in order; the "n-ary Cartesian product" of the lists.
    `static java.util.List<java.lang.Character>` | `charactersOf(java.lang.CharSequence sequence)` Returns a view of the specified `CharSequence` as a `List<Character>`, viewing `sequence` as a sequence of Unicode code units.
    `static ImmutableList<java.lang.Character>` | `charactersOf(java.lang.String string)` Returns a view of the specified string as an immutable list of `Character` values.
    `static <E> java.util.ArrayList<E>` | `newArrayList()` Creates a mutable, empty `ArrayList` instance (for Java 6 and earlier).
    `static <E> java.util.ArrayList<E>` | `newArrayList(E... elements)` Creates a mutable `ArrayList` instance containing the given elements.
    `static <E> java.util.ArrayList<E>` | `newArrayList(java.lang.Iterable<? extends E> elements)` Creates a mutable `ArrayList` instance containing the given elements; a very thin shortcut for creating an empty list then calling `Iterables.addAll(java.util.Collection<T>, java.lang.Iterable<? extends T>)`.
    `static <E> java.util.ArrayList<E>` | `newArrayList(java.util.Iterator<? extends E> elements)` Creates a mutable `ArrayList` instance containing the given elements; a very thin shortcut for creating an empty list and then calling `Iterators.addAll(java.util.Collection<T>, java.util.Iterator<? extends T>)`.
    `static <E> java.util.ArrayList<E>` | `newArrayListWithCapacity(int initialArraySize)` Creates an `ArrayList` instance backed by an array with the specified initial size; simply delegates to `ArrayList.ArrayList(int)`.
    `static <E> java.util.ArrayList<E>` | `newArrayListWithExpectedSize(int estimatedSize)` Creates an `ArrayList` instance to hold `estimatedSize` elements, plus an unspecified amount of padding; you almost certainly mean to call `newArrayListWithCapacity(int)` (see that method for further advice on usage).
    `static <E> java.util.concurrent.CopyOnWriteArrayList<E>` | `newCopyOnWriteArrayList()` Creates an empty `CopyOnWriteArrayList` instance.
    `static <E> java.util.concurrent.CopyOnWriteArrayList<E>` | `newCopyOnWriteArrayList(java.lang.Iterable<? extends E> elements)` Creates a `CopyOnWriteArrayList` instance containing the given elements.
    `static <E> java.util.LinkedList<E>` | `newLinkedList()` Creates a mutable, empty `LinkedList` instance (for Java 6 and earlier).
    `static <E> java.util.LinkedList<E>` | `newLinkedList(java.lang.Iterable<? extends E> elements)` Creates a mutable `LinkedList` instance containing the given elements; a very thin shortcut for creating an empty list then calling `Iterables.addAll(java.util.Collection<T>, java.lang.Iterable<? extends T>)`.
    `static <T> java.util.List<java.util.List<T>>` | `partition(java.util.List<T> list, int size)` Returns consecutive sublists of a list, each of the same size (the final list may be smaller).
    `static <T> java.util.List<T>` | `reverse(java.util.List<T> list)` Returns a reversed view of the specified list.
    `static <F,T> java.util.List<T>` | `transform(java.util.List<F> fromList, Function<? super F,? extends T> function)` Returns a list that applies `function` to each element of `fromList`.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Method Detail

    - #### newArrayList

          @GwtCompatible(serializable=true)
          public static <E> java.util.ArrayList<E> newArrayList()

      Creates a mutable, empty `ArrayList` instance (for Java 6 and earlier).

      Note: if mutability is not required, use `ImmutableList.of()` instead.

      Note for Java 7 and later: this method is now unnecessary and should be treated as deprecated. Instead, use the `ArrayList` constructor directly, taking advantage of the new "diamond" syntax.

    - #### newArrayList

          @GwtCompatible(serializable=true)
          public static <E> java.util.ArrayList<E> newArrayList(E... elements)

      Creates a mutable `ArrayList` instance containing the given elements.

      Note: essentially the only reason to use this method is when you will need to add or remove elements later. Otherwise, for non-null elements use `ImmutableList.of()` (for varargs) or `ImmutableList.copyOf(Object[])` (for an array) instead. If any elements might be null, or you need support for `List.set(int, Object)`, use `Arrays.asList(T...)`.

      Note that even when you do need the ability to add or remove, this method provides only a tiny bit of syntactic sugar for `newArrayList(``asList``(...))`, or for creating an empty list then calling `Collections.addAll(java.util.Collection<? super T>, T...)`. This method is not actually very useful and will likely be deprecated in the future.

    - #### newArrayList

          @GwtCompatible(serializable=true)
          public static <E> java.util.ArrayList<E> newArrayList(java.lang.Iterable<? extends E> elements)

      Creates a mutable `ArrayList` instance containing the given elements; a very thin shortcut for creating an empty list then calling `Iterables.addAll(java.util.Collection<T>, java.lang.Iterable<? extends T>)`.

      Note: if mutability is not required and the elements are non-null, use `ImmutableList.copyOf(Iterable)` instead. (Or, change `elements` to be a `FluentIterable` and call `elements.toList()`.)

      Note for Java 7 and later: if `elements` is a `Collection`, you don't need this method. Use the `ArrayList` constructor directly, taking advantage of the new "diamond" syntax.

    - #### newArrayList

          @GwtCompatible(serializable=true)
          public static <E> java.util.ArrayList<E> newArrayList(java.util.Iterator<? extends E> elements)

      Creates a mutable `ArrayList` instance containing the given elements; a very thin shortcut for creating an empty list and then calling `Iterators.addAll(java.util.Collection<T>, java.util.Iterator<? extends T>)`.

      Note: if mutability is not required and the elements are non-null, use `ImmutableList.copyOf(Iterator)` instead.

    - #### newArrayListWithCapacity

          @GwtCompatible(serializable=true)
          public static <E> java.util.ArrayList<E> newArrayListWithCapacity(int initialArraySize)

      Creates an `ArrayList` instance backed by an array with the specified initial size; simply delegates to `ArrayList.ArrayList(int)`.

      Note for Java 7 and later: this method is now unnecessary and should be treated as deprecated. Instead, use `new` `ArrayList``<>(int)` directly, taking advantage of the new "diamond" syntax. (Unlike here, there is no risk of overload ambiguity, since the `ArrayList` constructors very wisely did not accept varargs.)

      Parameters:
        `initialArraySize` - the exact size of the initial backing array for the returned array list (`ArrayList` documentation calls this value the "capacity")
      Returns:
        a new, empty `ArrayList` which is guaranteed not to resize itself unless its size reaches `initialArraySize + 1`
      Throws:
        `java.lang.IllegalArgumentException` - if `initialArraySize` is negative

    - #### newArrayListWithExpectedSize

          @GwtCompatible(serializable=true)
          public static <E> java.util.ArrayList<E> newArrayListWithExpectedSize(int estimatedSize)

      Creates an `ArrayList` instance to hold `estimatedSize` elements, plus an unspecified amount of padding; you almost certainly mean to call `newArrayListWithCapacity(int)` (see that method for further advice on usage).

      Note: This method will soon be deprecated. Even in the rare case that you do want some amount of padding, it's best if you choose your desired amount explicitly.

      Parameters:
        `estimatedSize` - an estimate of the eventual `List.size()` of the new list
      Returns:
        a new, empty `ArrayList`, sized appropriately to hold the estimated number of elements
      Throws:
        `java.lang.IllegalArgumentException` - if `estimatedSize` is negative

    - #### newLinkedList

          @GwtCompatible(serializable=true)
          public static <E> java.util.LinkedList<E> newLinkedList()

      Creates a mutable, empty `LinkedList` instance (for Java 6 and earlier).

      Note: if you won't be adding any elements to the list, use `ImmutableList.of()` instead.

      Performance note: `ArrayList` and `ArrayDeque` consistently outperform `LinkedList` except in certain rare and specific situations. Unless you have spent a lot of time benchmarking your specific needs, use one of those instead.

      Note for Java 7 and later: this method is now unnecessary and should be treated as deprecated. Instead, use the `LinkedList` constructor directly, taking advantage of the new "diamond" syntax.

    - #### newLinkedList

          @GwtCompatible(serializable=true)
          public static <E> java.util.LinkedList<E> newLinkedList(java.lang.Iterable<? extends E> elements)

      Creates a mutable `LinkedList` instance containing the given elements; a very thin shortcut for creating an empty list then calling `Iterables.addAll(java.util.Collection<T>, java.lang.Iterable<? extends T>)`.

      Note: if mutability is not required and the elements are non-null, use `ImmutableList.copyOf(Iterable)` instead. (Or, change `elements` to be a `FluentIterable` and call `elements.toList()`.)

      Performance note: `ArrayList` and `ArrayDeque` consistently outperform `LinkedList` except in certain rare and specific situations. Unless you have spent a lot of time benchmarking your specific needs, use one of those instead.

      Note for Java 7 and later: if `elements` is a `Collection`, you don't need this method. Use the `LinkedList` constructor directly, taking advantage of the new "diamond" syntax.

    - #### newCopyOnWriteArrayList

          @GwtIncompatible(value="CopyOnWriteArrayList")
          public static <E> java.util.concurrent.CopyOnWriteArrayList<E> newCopyOnWriteArrayList()

      Creates an empty `CopyOnWriteArrayList` instance.

      Note: if you need an immutable empty `List`, use `Collections.emptyList()` instead.

      Returns:
        a new, empty `CopyOnWriteArrayList`
      Since:
        12.0

    - #### newCopyOnWriteArrayList

          @GwtIncompatible(value="CopyOnWriteArrayList")
          public static <E> java.util.concurrent.CopyOnWriteArrayList<E> newCopyOnWriteArrayList(java.lang.Iterable<? extends E> elements)

      Creates a `CopyOnWriteArrayList` instance containing the given elements.
      Parameters:
        `elements` - the elements that the list should contain, in order
      Returns:
        a new `CopyOnWriteArrayList` containing those elements
      Since:
        12.0

    - #### asList

          public static <E> java.util.List<E> asList(@Nullable
                                     E first,
                                     E[] rest)

      Returns an unmodifiable list containing the specified first element and backed by the specified array of additional elements. Changes to the `rest` array will be reflected in the returned list. Unlike `Arrays.asList(T...)`, the returned list is unmodifiable.

      This is useful when a varargs method needs to use a signature such as `(Foo firstFoo, Foo... moreFoos)`, in order to avoid overload ambiguity or to enforce a minimum argument count.

      The returned list is serializable and implements `RandomAccess`.

      Parameters:
        `first` - the first element
        `rest` - an array of additional elements, possibly empty
      Returns:
        an unmodifiable list containing the specified elements

    - #### asList

          public static <E> java.util.List<E> asList(@Nullable
                                     E first,
                                     @Nullable
                                     E second,
                                     E[] rest)

      Returns an unmodifiable list containing the specified first and second element, and backed by the specified array of additional elements. Changes to the `rest` array will be reflected in the returned list. Unlike `Arrays.asList(T...)`, the returned list is unmodifiable.

      This is useful when a varargs method needs to use a signature such as `(Foo firstFoo, Foo secondFoo, Foo... moreFoos)`, in order to avoid overload ambiguity or to enforce a minimum argument count.

      The returned list is serializable and implements `RandomAccess`.

      Parameters:
        `first` - the first element
        `second` - the second element
        `rest` - an array of additional elements, possibly empty
      Returns:
        an unmodifiable list containing the specified elements

    - #### cartesianProduct

          public static <B> java.util.List<java.util.List<B>> cartesianProduct(java.util.List<? extends java.util.List<? extends B>> lists)

      Returns every possible list that can be formed by choosing one element from each of the given lists in order; the "n-ary Cartesian product" of the lists. For example:

             Lists.cartesianProduct(ImmutableList.of(
                 ImmutableList.of(1, 2),
                 ImmutableList.of("A", "B", "C")))

      returns a list containing six lists in the following order:

      - `ImmutableList.of(1, "A")`
      - `ImmutableList.of(1, "B")`
      - `ImmutableList.of(1, "C")`
      - `ImmutableList.of(2, "A")`
      - `ImmutableList.of(2, "B")`
      - `ImmutableList.of(2, "C")`

      The result is guaranteed to be in the "traditional", lexicographical order for Cartesian products that you would get from nesting for loops:

             for (B b0 : lists.get(0)) {
               for (B b1 : lists.get(1)) {
                 ...
                 ImmutableList<B> tuple = ImmutableList.of(b0, b1, ...);
                 // operate on tuple
               }
             }

      Note that if any input list is empty, the Cartesian product will also be empty. If no lists at all are provided (an empty list), the resulting Cartesian product has one element, an empty list (counter-intuitive, but mathematically consistent).

      Performance notes: while the cartesian product of lists of size `m, n, p` is a list of size `m x n x p`, its actual memory consumption is much smaller. When the cartesian product is constructed, the input lists are merely copied. Only as the resulting list is iterated are the individual lists created, and these are not retained after iteration.

      Type Parameters:
        `B` - any common base class shared by all axes (often just `Object`)
      Parameters:
        `lists` - the lists to choose elements from, in the order that the elements chosen from those lists should appear in the resulting lists
      Returns:
        the Cartesian product, as an immutable list containing immutable lists
      Throws:
        `java.lang.IllegalArgumentException` - if the size of the cartesian product would be greater than `Integer.MAX_VALUE`
        `java.lang.NullPointerException` - if `lists`, any one of the `lists`, or any element of a provided list is null
      Since:
        19.0

    - #### cartesianProduct

          public static <B> java.util.List<java.util.List<B>> cartesianProduct(java.util.List<? extends B>... lists)

      Returns every possible list that can be formed by choosing one element from each of the given lists in order; the "n-ary Cartesian product" of the lists. For example:

             Lists.cartesianProduct(ImmutableList.of(
                 ImmutableList.of(1, 2),
                 ImmutableList.of("A", "B", "C")))

      returns a list containing six lists in the following order:

      - `ImmutableList.of(1, "A")`
      - `ImmutableList.of(1, "B")`
      - `ImmutableList.of(1, "C")`
      - `ImmutableList.of(2, "A")`
      - `ImmutableList.of(2, "B")`
      - `ImmutableList.of(2, "C")`

      The result is guaranteed to be in the "traditional", lexicographical order for Cartesian products that you would get from nesting for loops:

             for (B b0 : lists.get(0)) {
               for (B b1 : lists.get(1)) {
                 ...
                 ImmutableList<B> tuple = ImmutableList.of(b0, b1, ...);
                 // operate on tuple
               }
             }

      Note that if any input list is empty, the Cartesian product will also be empty. If no lists at all are provided (an empty list), the resulting Cartesian product has one element, an empty list (counter-intuitive, but mathematically consistent).

      Performance notes: while the cartesian product of lists of size `m, n, p` is a list of size `m x n x p`, its actual memory consumption is much smaller. When the cartesian product is constructed, the input lists are merely copied. Only as the resulting list is iterated are the individual lists created, and these are not retained after iteration.

      Type Parameters:
        `B` - any common base class shared by all axes (often just `Object`)
      Parameters:
        `lists` - the lists to choose elements from, in the order that the elements chosen from those lists should appear in the resulting lists
      Returns:
        the Cartesian product, as an immutable list containing immutable lists
      Throws:
        `java.lang.IllegalArgumentException` - if the size of the cartesian product would be greater than `Integer.MAX_VALUE`
        `java.lang.NullPointerException` - if `lists`, any one of the `lists`, or any element of a provided list is null
      Since:
        19.0

    - #### transform

          @CheckReturnValue
          public static <F,T> java.util.List<T> transform(java.util.List<F> fromList,
                                                           Function<? super F,? extends T> function)

      Returns a list that applies `function` to each element of `fromList`. The returned list is a transformed view of `fromList`; changes to `fromList` will be reflected in the returned list and vice versa.

      Since functions are not reversible, the transform is one-way and new items cannot be stored in the returned list. The `add`, `addAll` and `set` methods are unsupported in the returned list.

      The function is applied lazily, invoked when needed. This is necessary for the returned list to be a view, but it means that the function will be applied many times for bulk operations like `List.contains(java.lang.Object)` and `List.hashCode()`. For this to perform well, `function` should be fast. To avoid lazy evaluation when the returned list doesn't need to be a view, copy the returned list into a new list of your choosing.

      If `fromList` implements `RandomAccess`, so will the returned list. The returned list is threadsafe if the supplied list and function are.

      If only a `Collection` or `Iterable` input is available, use `Collections2.transform(java.util.Collection<F>, com.google.common.base.Function<? super F, T>)` or `Iterables.transform(java.lang.Iterable<F>, com.google.common.base.Function<? super F, ? extends T>)`.

      Note: serializing the returned list is implemented by serializing `fromList`, its contents, and `function` -- not by serializing the transformed values. This can lead to surprising behavior, so serializing the returned list is not recommended. Instead, copy the list using `ImmutableList.copyOf(Collection)` (for example), then serialize the copy. Other methods similar to this do not implement serialization at all for this reason.

    - #### partition

          public static <T> java.util.List<java.util.List<T>> partition(java.util.List<T> list,
                                                        int size)

      Returns consecutive sublists of a list, each of the same size (the final list may be smaller). For example, partitioning a list containing `[a, b, c, d, e]` with a partition size of 3 yields `[[a, b, c], [d, e]]` -- an outer list containing two inner lists of three and two elements, all in the original order.

      The outer list is unmodifiable, but reflects the latest state of the source list. The inner lists are sublist views of the original list, produced on demand using `List.subList(int, int)`, and are subject to all the usual caveats about modification as explained in that API.

      Parameters:
        `list` - the list to return consecutive sublists of
        `size` - the desired size of each sublist (the last may be smaller)
      Returns:
        a list of consecutive sublists
      Throws:
        `java.lang.IllegalArgumentException` - if `partitionSize` is nonpositive

    - #### charactersOf

          @Beta
          public static ImmutableList<java.lang.Character> charactersOf(java.lang.String string)

      Returns a view of the specified string as an immutable list of `Character` values.
      Since:
        7.0

    - #### charactersOf

          @Beta
          public static java.util.List<java.lang.Character> charactersOf(java.lang.CharSequence sequence)

      Returns a view of the specified `CharSequence` as a `List<Character>`, viewing `sequence` as a sequence of Unicode code units. The view does not support any modification operations, but reflects any changes to the underlying character sequence.
      Parameters:
        `sequence` - the character sequence to view as a `List` of characters
      Returns:
        an `List<Character>` view of the character sequence
      Since:
        7.0

    - #### reverse

          @CheckReturnValue
          public static <T> java.util.List<T> reverse(java.util.List<T> list)

      Returns a reversed view of the specified list. For example, `Lists.reverse(Arrays.asList(1, 2, 3))` returns a list containing `3, 2, 1`. The returned list is backed by this list, so changes in the returned list are reflected in this list, and vice-versa. The returned list supports all of the optional list operations supported by this list.

      The returned list is random-access if the specified list is random access.

      Since:
        7.0