Java Guava | Lists.partition() method with Examples

The Lists.partition() method in Guava Library is used to divide the original list into sublists of the same size. The method accepts two parameters.

For example: If the original list passed as parameter is [a, b, c, d, e] and the partition size is 3, then the sublists yield are as [[a, b, c], [d, e]].

Syntax:

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

Parameters: The method accepts two parameters:

• list: The list which is to be divided into sublists based on the partition size.
• size: The desired size of each sublist. The size of the last sublist may be smaller.

Return Value: The method returns the list of consecutive sublists. Each sublist(except possibly the last one) has the size equal to the partition size.

Exception: The method Lists.partition() throws IllegalArgumentException if partition size is non-positive.

Below examples illustrate the implementation of above method:

Example 1:

// Java code to show implementation of
// Guava's Lists.partition() method

import com.google.common.collect.Lists;
import java.util.Arrays;
import java.util.List;

class GFG {

    // Driver's code
    public static void main(String[] args)
    {
        // Creating a List of Integers
        List<Integer> myList
            = Arrays.asList(1, 2, 3, 4, 5);

        // Using Lists.partition() method to divide
        // the original list into sublists of the same
        // size, which are just views of the original list.
        // The final list may be smaller.
        List<List<Integer> > lists
            = Lists.partition(myList, 2);

        // Displaying the sublists
        for (List<Integer> sublist: lists)
            System.out.println(sublist);
    }
}

Output:

[1, 2]
[3, 4]
[5]

Example 2:

// Java code to show implementation of
// Guava's Lists.partition() method

import com.google.common.collect.Lists;
import java.util.Arrays;
import java.util.List;

class GFG {

    // Driver's code
    public static void main(String[] args)
    {

        // Creating a List of Characters
        List<Character> myList
            = Arrays.asList('H', 'E', 'L', 'L', 'O',
                            'G', 'E', 'E', 'K', 'S');

        // Using Lists.partition() method to divide
        // the original list into sublists of the same
        // size, which are just views of the original list.
        // The final list may be smaller.
        List<List<Character> > lists
            = Lists.partition(myList, 3);

        // Displaying the sublists
        for (List<Character> sublist: lists)
            System.out.println(sublist);
    }
}

Output:

[H, E, L]
[L, O, G]
[E, E, K]
[S]

Reference: https://google.github.io/guava/releases/23.0/api/docs/com/google/common/collect/Lists.html#partition-java.util.List-int-