A lambda expression is one or more line of code which works like function or method. It takes a parameter and returns the value. Lambda expression can be used to convert ArrayList to HashMap.
Syntax:
(parms1, parms2) -> expression
Examples:
Input : List : [1="1", 2="2", 3="3"] Output: Map : {1=1, 2=2, 3=3, 4=4, 5=5} Input : List : [1="I", 2="love", 3="Geeks" , 4="for" , 5="Geeks"] Output: Map : {1=I, 2=Love, 3=Geeks, 4=For, 5=Geeks}
Approach:
- Get the List to be converted into Map
- Create an empty Map
- Put the list values to the map using Lambda Expression
- Return the formed Map
Below is the implementation of the above approach.
Java
// Converting ArrayList to HashMap // in Java 8 using a Lambda Expression import java.util.*;
import java.util.ArrayList;
import java.util.Scanner;
// here we are making a class , and we will make class ListItems {
// key will act as an id of the value
private Integer key;
// value will be the value of the above key
private String value;
// create constructor for reference
public ListItems(Integer id, String name)
{
// assigning the value of key and value
this .key = id;
this .value = name;
}
// return private variable key
public Integer getkey() { return key; }
// return private variable name
public String getvalue() { return value; }
} class Main {
public static void main(String[] args)
{
// Write your code here
// Creating a List of type ListItems using ArrayList
List<ListItems> list = new ArrayList<ListItems>();
// add the member of list
list.add( new ListItems( 1 , "I" ));
list.add( new ListItems( 2 , "Love" ));
list.add( new ListItems( 3 , "Geeks" ));
list.add( new ListItems( 4 , "For" ));
list.add( new ListItems( 5 , "Geeks" ));
// Map which will store the list items
Map<Integer, String> map = new HashMap<>();
// for (ListItems n : list) { map.put(n.getkey(),
// n.getvalue()); }
// the below lambda performs the same task as the
// above given for loop will do
// put the list items in the Map
list.forEach(
(n) -> { map.put(n.getkey(), n.getvalue()); });
// Printing the given map
System.out.println( "Map : " + map);
}
} |
Output
Map : {1=I, 2=Love, 3=Geeks, 4=For, 5=Geeks}
Time Complexity: O(N), where N is the length of Arraylist.