Java: Examples of the Java list/array `subList` method (list subset)

By Alvin Alexander. Last updated: June 27, 2019

As a little note today, if you ever need to extract a subset of a Java list or array, here are some examples of the Java subList method:

import java.util.*;

public class SubList {

    public static void main(String[] args) {

        List<String> x = new ArrayList<>();
        x.add("a");
        x.add("b");
        x.add("c");
        x.add("d");
        x.add("e");

        // `subList(int fromIndex, int toIndex)`
        // array indexes start at 0.
        // 1st arg is inclusive (included), 2nd arg is exclusive (not included).
        List a = x.subList(0,1);  // [a]
        List b = x.subList(0,2);  // [a, b]
        List c = x.subList(0,4);  // [a, b, c, d]      # same as `x.subList(0,x.size()-1)`
        List d = x.subList(0,5);  // [a, b, c, d, e]   # same as `x.subList(0,x.size())`
        List e = x.subList(0,6);  // IndexOutOfBoundsException
        List f = x.subList(1,1);  // f []
        List g = x.subList(1,2);  // g [b]
        List h = x.subList(2,5);  // h [c, d, e]
        
    }
}

If you print the results of each line you’ll see the results on the right side of the comments. As shown:

The first element in a list or array is at index 0
The toIndex is exclusive, meaning it won’t be included in the results
If you go outside the size of the initial list, you’ll get an IndexOutOfBoundsException
The original list isn’t modified; if you print x, you’ll see that it still includes all of the original elements

If you ever need to extract a subset of a Java list or array into another list or array, I hope these Java subList examples are helpful.

java

array