Iterate List in Reverse Order in Java
Last Updated :
28 Dec, 2020
The List interface provides a way to store the ordered collection. It is a child interface of Collection. It is an ordered collection of objects in which duplicate values can be stored. Since List preserves the insertion order, it allows positional access and insertion of elements.
Example
Input: ["geeks", "for", "Geeks"]
Output: ["Geeks", "for", "geeks"]
Input: [ 1, 2, 3, 4, 5]
output: [5, 4, 3, 2, 1]
We can iterate the list in reverse order in two ways:
- Using List.listIterator() and Using for loop method.
- Using IntStream range(int startInclusive, int endExclusive).
Approach 1: Using List.listIterator() and Using for loop method.
Syntax:
public ListIterator listIterator()
Return Value: This method returns a list iterator over the elements in this list (in proper sequence).
- This allows bidirectional access.
- List.listIterator() method is used to get a ListIterator over the elements in a list starting from specified position in the list. If we need to start from the last element, the starting Index would be equal to the size of the list.
Syntax:
ListIterator<Integer> listIterator( Index )
Index = Index from where list element will reverse till index = 0.
Java
import java.util.*;
class GFG {
public static void main(String[] args)
{
List<String> list = new ArrayList<String>();
list.add("GEEKS");
list.add("for");
list.add("geeks");
ListIterator<String> gfg_itr
= list.listIterator(list.size());
while (gfg_itr.hasPrevious())
{
System.out.println(gfg_itr.previous());
}
for (int i = list.size() - 1; i >= 0; i--)
{
System.out.println(list.get(i));
}
}
}
|
Output
geeks
for
GEEKS
geeks
for
GEEKS
Approach 2: Using IntStream range(int startInclusive, int endExclusive)
- This returns a sequential ordered IntStream from startInclusive (inclusive) to endExclusive (exclusive) by an incremental step of 1. It correctly handles overflow.
Syntax :
static IntStream range(int startInclusive, int endExclusive)
Parameters :
- IntStream : A sequence of primitive int-valued elements.
- startInclusive : The inclusive initial value.
- endExclusive : The exclusive upper bound.
Java
import java.util.*;
import java.util.stream.IntStream;
class GFG {
public static void main(String[] args)
{
List<Integer> list_li = new ArrayList<Integer>();
list_li.add(1);
list_li.add(2);
list_li.add(3);
list_li.add(4);
list_li.add(5);
IntStream stream = IntStream.range(0, list_li.size());
stream.map(i -> list_li.size() - i - 1).map(list_li::get)
.forEach(System.out::println);
}
}
|
Note: IntStream range(int startInclusive, int endExclusive) basically works like a for loop. An equivalent sequence of increasing values can be produced sequentially as :
for (int i = startInclusive; i < endExclusive ; i++)
{
...
...
...
}
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