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# Split a List into Two Halves in Java

Here we are given a list and the task is to split it into two news lists as one can better perceive from the below illustration as follows:

Illustration:

```Input  : list = {1, 2, 3, 4, 5, 6}
Output : first = {1, 2, 3}, second = {4, 5, 6}

Input  : list = {1, 2, 3, 4, 5}
Output : first = {1, 2}, second = {3, 4, 5}```

Methods:

1. Using loops(Naive Approach)
2. Using subList() method of List class
3. Using partitioningBy() method of Collectors class

Let us do discuss the above-defined methods to details alongside implementing via clean java programs as follows:

Method 1: Using loops

Approach:

1. Create two new empty lists and assign the first half element of the original list.
2. Reset into the second empty list.

Example:

## Java

 `// Java Program to Split a List into Two Sublist` `// Importing required classes``import` `java.util.ArrayList;``import` `java.util.List;` `// Main class``public` `class` `GFG {` `    ``// Method 1``    ``// To split a list into two sublists in Java``    ``public` `static` `List[] split(List list)``    ``{` `        ``// Creating two empty lists``        ``List first = ``new` `ArrayList();``        ``List second = ``new` `ArrayList();` `        ``// Getting size of the list``        ``// using size() method``        ``int` `size = list.size();` `        ``// Step 1``        ``// (First size)/2 element copy into list``        ``// first and rest second list``        ``for` `(``int` `i = ``0``; i < size / ``2``; i++)``            ``first.add(list.get(i));` `        ``// Step 2``        ``// (Second size)/2 element copy into list first and``        ``// rest second list``        ``for` `(``int` `i = size / ``2``; i < size; i++)``            ``second.add(list.get(i));` `        ``// Returning a List of array``        ``return` `new` `List[] { first, second };``    ``}` `    ``// Method 2``    ``// Main driver method``    ``public` `static` `void` `main(String[] args)``    ``{` `        ``// Creating an ArrayList of string type``        ``List list = ``new` `ArrayList();` `        ``// Adding elements to list object``        ``// using add() method``        ``list.add(``"Geeks"``);``        ``list.add(``"Practice"``);``        ``list.add(``"Contribute"``);``        ``list.add(``"IDE"``);``        ``list.add(``"Courses"``);` `        ``// Calling split method which return List of array``        ``List[] lists = split(list);` `        ``// Printing specific elements of list by``        ``// passing arguments with in``        ``System.out.println(lists[``0``]);``        ``System.out.println(lists[``1``]);``    ``}``}`

Output

```[Geeks, Practice]
[Contribute, IDE, Courses]```

Method 2: Using subList() method of List class

It returns a view of the portion of this list between the specified index(include) to another index (exclude). For example, let us take arbitrarily from 2 to 5, Here index 2 will include only. In case if both specified indexes are equal, the returned list is empty. The List.subList() returned a list, so non-structural changes in the returned list.

Example:

## Java

 `// Java Program to Split a List into Two SubList``// Using subList() method of List class` `// Importing required classes``import` `java.util.ArrayList;``import` `java.util.List;` `// Main class``public` `class` `GFG {` `    ``// Method 1``    ``// To split a list into two sublists in Java``    ``public` `static` `List[] split(List list)``    ``{` `        ``// Finding the size of the list using List.size()``        ``// and putting in a variable``        ``int` `size = list.size();` `        ``// Creating new list and inserting values which is``        ``// returned by List.subList() method``        ``List first``            ``= ``new` `ArrayList<>(list.subList(``0``, (size) / ``2``));``        ``List second = ``new` `ArrayList<>(``            ``list.subList((size) / ``2``, size));` `        ``// Returning an List of array``        ``return` `new` `List[] { first, second };``    ``}` `    ``// Method 2``    ``// Main driver method``    ``public` `static` `void` `main(String[] args)``    ``{` `        ``// Creatingan ArrayList of String type``        ``List list = ``new` `ArrayList();` `        ``// Adding elements to List object``        ``// Custom input elements``        ``list.add(``"Geeks"``);``        ``list.add(``"Practice"``);``        ``list.add(``"Contribute"``);``        ``list.add(``"IDE"``);``        ``list.add(``"Courses"``);` `        ``// Calling split method which return List of array``        ``List[] lists = split(list);` `        ``// Printing specific elements of list by``        ``// passing arguments with in``        ``System.out.println(lists[``0``]);``        ``System.out.println(lists[``1``]);``    ``}``}`

Output

```[Geeks, Practice]
[Contribute, IDE, Courses]```

Method 3: Using partitioningBy() method of Collectors class

Java 8 Collectors.partitioningBy() is a method that partitions the elements of stream always in two-part, unlike Naive and List.subList(). It returns a Collector that stores the values in a Map. The key of the map can be only in Boolean.

Syntax: partitioningBy() method

```public static  Collector<T, ?, Map<Boolean, List>>
partitioningBy(Predicate predicate)```

Example:

## Java

 `// Java Program to Split a List into Two Sub-List``/// Using partitioningBy() method of Collectors class` `// Importing required classes``import` `java.util.ArrayList;``import` `java.util.List;``import` `java.util.stream.Collectors;` `// Main class``public` `class` `GFG {` `    ``// Method 1``    ``// To split a list into two sublists in Java``    ``public` `static` `List[] split(List list)``    ``{` `        ``// Setting value of midIndex using comparators``        ``int` `midIndex``            ``= ((list.size() / ``2``)``               ``- (((list.size() % ``2``) > ``0``) ? ``0` `: ``1``));` `        ``// Creating object of List with reference to``        ``// ArrayList class Declaring object List``        ``// type``        ``List > lists = ``new` `ArrayList<>(``            ``list.stream()``                ``.collect(Collectors.partitioningBy(``                    ``s -> list.indexOf(s) > midIndex))``                ``.values());` `        ``// Returning an array containing both lists``        ``return` `new` `List[] { lists.get(``0``), lists.get(``1``) };``    ``}` `    ``// Method 2``    ``// Main driver method``    ``public` `static` `void` `main(String[] args)``    ``{` `        ``// Creating an ArrayList of String type``        ``List list = ``new` `ArrayList();` `        ``// Adding elements to List object``        ``// Using add() method``        ``list.add(``"Geeks"``);``        ``list.add(``"Practice"``);``        ``list.add(``"Contribute"``);``        ``list.add(``"IDE"``);``        ``list.add(``"Courses"``);` `        ``// Calling split method which return List of array``        ``List[] lists = split(list);` `        ``// Printing specific elements of list by``        ``// passing arguments with in``        ``System.out.println(lists[``0``]);``        ``System.out.println(lists[``1``]);``    ``}``}`

Output

```[Geeks, Practice, Contribute]
[IDE, Courses]```

Method 4: Using Google guava Library

Guava is an open-source Java-based library which is developed by Google Inc. In the Guava library, we can use Lists.partition() method that splits the list into consecutive sublists, every list specified size. In order to split the list into two sublists, In our case, we can pass the size that is equal to half the size of our list.

Example

## Java

 `// Java Program to Split a List into Two Sub-List` `// Importing Guava library``import` `com.google.common.collect.Iterables;``// Importing required classes``import` `java.util.ArrayList;``import` `java.util.Iterator;``import` `java.util.List;` `// Main class``public` `class` `GFG {` `    ``// Method 1``    ``// To split a list into two sublists in Java``    ``public` `static` `List[] split(List list)``    ``{` `        ``// Partition the List into two sublists and``        ``// getting iterator``        ``Iterator > itr``            ``= Iterables.partition(list, (list.size()) / ``2``)``                  ``.iterator();` `        ``// Returning an array containing both lists``        ``return` `new` `List[] { ``new` `ArrayList<>(itr.next()),``                            ``new` `ArrayList<>(itr.next()) };``    ``}` `    ``// Method 2``    ``// Main driver method``    ``public` `static` `void` `main(String[] args)``    ``{` `        ``// Creating an ArrayList of string type``        ``List list = ``new` `ArrayList();` `        ``// Adding elements t oabove object``        ``// Custom input elements``        ``list.add(``"Geeks"``);``        ``list.add(``"Practice"``);``        ``list.add(``"Contribute"``);``        ``list.add(``"IDE"``);``        ``list.add(``"Courses"``);` `        ``// Calling split method which return List of array``        ``List[] lists = split(list);` `        ``// Printing specific elements of list by``        ``// passing arguments with in``        ``System.out.println(lists[``0``]);``        ``System.out.println(lists[``1``]);``    ``}``}`

Output

```[Geeks, Practice]
[Contribute, IDE]```

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