Java-Collectors toMap

Collectors toMap

The Collectors class provides a large number of static methods for common collectors. The toMap( ) method of the collectors is used to collect stream elements into a Map.  The toMap( ) method has three forms. The first is:

If the mapped keys contain duplicates (according to Object.equals(Object)), an IllegalStateException is thrown when the collection operation is performed. For example, consider the following example:

In this example, mapped keys have duplicates so the IllegalStateException is thrown. If the mapped keys might have duplicates, use the following form of toMap method to prevent this exception:

If you want to get specific type Map, use the following form of toMap:

Program

Program Source

import java.util.stream.Stream;
import java.util.stream.Collectors;
import java.util.HashMap;

public class Javaapp {

    public static void main(String[] args) {
        
        String strary[] = {"Ida","Jack","Lia","Bryan","Edmund","Logan"};
        Stream<String> strstm = Stream.of(strary);
        HashMap<Integer,String> mp;
        mp = strstm.collect(Collectors.toMap((a)->a.length(), (a)->a, (a,b)->a+" / "+b, HashMap::new));
        System.out.println(mp);
    }
}