import java.util.*;
import java.util.stream.Collectors;
public class ListToMap {
public static void main(String[] args) {
List list = Arrays.asList("apple", "banana", "cherry", "date", "1","2");
Map map = list.stream()
.collect(Collectors.toMap(
String::length, // Key is the length of the string
str -> str, // Value is the string itself
(existing, replacement) -> {
System.out.println("Duplicate key detected: " + existing + " and " + replacement);
return existing; // Keep the existing value
}));
System.out.println(map);
// To return both existing & replacement
// Create a Map where the key is the string length and the value is a List of
// Strings
Map> mapforExistingReplacement = list.stream()
.collect(Collectors.toMap(
String::length, // Key is the length of the string
str -> new ArrayList<>(Collections.singletonList(str)), // Initialize with the first value in a
// list
(existing, replacement) -> {
existing.addAll(replacement); // Add the replacement to the existing list
return existing; // Return the updated list
}));
// Map map = list.stream()
// .collect(Collectors.toMap(String::length, str -> str));
System.out.println(mapforExistingReplacement);
// Using a Set for Unique Values
// If you want to avoid duplicates and store each value only once, you can use a
// Set instead of a List. A Set will automatically handle duplicate entries.
// Create a Map where the key is the string length and the value is a Set of Strings
Map> mapToSetMap = list.stream()
.collect(Collectors.toMap(
String::length, // Key is the length of the string
str -> new HashSet<>(Collections.singletonList(str)), // Initialize with the first value in a Set
(existing, replacement) -> {
existing.addAll(replacement); // Add the replacement to the existing Set
return existing; // Return the updated Set
}
));
System.out.println("maptoSetMap " +mapToSetMap);
//map to list
Map> mapToList = list.stream()
.collect(Collectors.groupingBy(
String::length, // Key is the length of the string
Collectors.toList() // Value is a List of strings
));
System.out.println("mapToList " + mapToList);
}
}