Get a sublist of a list in Java

This post will discuss how to get a sublist of a list between two specified indexes in Java.

1. Naive solution

A naive solution is to add elements from the original list present between the specified indexes to the sublist.

// Generic method to get a sublist of a list between two specified indexes

public static<T> List<T> sublist(List<T> list, int start, int end)

{

// create an empty list

List<T> subList = new ArrayList<>();

// add desired elements from the original list to the sublist

for (int i = start; i <= end; i++) {

subList.add(list.get(i));

}

// return the sublist

return subList;

}

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2. Using `List.sublist()` method

We can also use the sublist() method provided by the List interface that returns a “view” of the portion of the list between the specified indexes.

// Generic method to get a sublist of a list between two specified indexes

public static<T> List<T> sublist(List<T> list, int start, int end) {

return list.subList(start, end + 1);

}

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⮚ IndexOutOfBoundsException

The subList() method throws IndexOutOfBoundsException if starting or ending index is illegal. For instance,

start < 0
end > list.size()
start > end

To avoid IndexOutOfBoundsException from happening, we can check if indexes are within proper bounds before passing to sublist(), as shown below:

// Generic method to get a sublist of a list between two specified indexes

public static<T> List<T> sublist(List<T> list, int start, int end) {

return list.subList(Math.max(0, start), Math.min(list.size(), end + 1));

}

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⮚ ConcurrentModificationException

Since the list returned by list.subList() is backed by the list, any non-structural changes (that do not change the size of the list) in the sublist are reflected in the original list and vice-versa. If the backing list is structurally modified in any way, the behavior of the list is undefined, and ConcurrentModificationException may be thrown.

// Generic method to get a sublist of a list between two specified indexes

public static<T> List<T> sublist(List<T> list, int start, int end)

{

List<T> subList = list.subList(start, end + 1);

list.remove(2); // lead to `ConcurrentModificationException`

return subList;

}

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Output:

Exception in thread “main” java.util.ConcurrentModificationException
at java.util.ArrayList$SubList.checkForComodification(ArrayList.java:1231)
at java.util.ArrayList$SubList.listIterator(ArrayList.java:1091)
at java.util.AbstractList.listIterator(AbstractList.java:299)
at java.util.ArrayList$SubList.iterator(ArrayList.java:1087)
at java.util.AbstractCollection.toString(AbstractCollection.java:454)
at java.lang.String.valueOf(String.java:2994)
at java.lang.StringBuilder.append(StringBuilder.java:131)
at Main.main(Main.java:23)

The solution to this problem is to create a new list from the returned view by subList(), as shown below:

// Generic method to get a sublist of a list between two specified indexes

public static<T> List<T> sublist(List<T> list, int start, int end)

{

List<T> subList = new ArrayList<>(list.subList(start, end + 1));

list.remove(2); // ConcurrentModificationException not thrown

return subList;

}

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That’s all about getting a sublist of a list in Java.

Reference: List Javadoc SE 8

Get a sublist of a list in Java

1. Naive solution

2. Using List.sublist() method

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2. Using `List.sublist()` method