Baeldung
baeldung.com › home › java › java collections › java map › get values and keys as arraylist from a hashmap
Get Values and Keys as ArrayList From a HashMap | Baeldung
March 7, 2025 - When we manipulate data structures in Java, one common scenario involves extracting values and keys from a HashMap and organizing them into an ArrayList. In this quick tutorial, we’ll explore various practical approaches to achieving this goal.
GeeksforGeeks
geeksforgeeks.org › java › conversion-of-java-maps-to-list
Conversion of Java Map to List - GeeksforGeeks
July 11, 2025 - The Map interface provides a method keySet() that returns a set of all the keys in the map. We can convert this set into a list using the ArrayList constructor. Example: This example demonstrates how to convert the keys of a Map into a List in Java.
How do I convert a Map to List in Java? - Stack Overflow
I was assuming the cast from Collection to List would work. 2013-06-18T21:28:08.72Z+00:00 ... Sheldon R. Over a year ago · I suspect the reason it doesn't work is because the collection returned by values() is dependent on the underlying Map; by making a copy constructor call instead, you allocate storage and copy the values into that storage, thus breaking the connection... 2013-11-22T16:14:13.183Z+00:00 ... @SheldonR. yes - the collections returned by keySet... More on stackoverflow.com
java - convert map to list<string> - as "key-value" to each list entry - Stack Overflow
I want to convert Map to List with each map entry - to 1 entry in the list as "key - value" I searched and I only found to map values only to List. Map More on stackoverflow.com
How to fetch a List which is a "value" in Map?
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October 21, 2022java - How to convert hash map keys into list? - Stack Overflow
I have a hash map and I'm trying to convert the keys to a list. Here's the code: List recs = new ArrayList (); HashMap uniqueRecs = new HashMap... More on stackoverflow.com
Vultr Docs
docs.vultr.com › java › examples › convert map (hashmap) to list
Java Program to Convert Map (HashMap) to List
December 12, 2024 - Create a HashMap and populate it with sample data. Utilize the keySet() method to extract the keys, then construct a List using the ArrayList constructor. ... import java.util.*; public class Main { public static void main(String[] args) { ...
Mkyong
mkyong.com › home › java8 › java 8 – convert map to list
Java 8 – Convert Map to List | mkyong.com
May 24, 2017 - Map<String, String> map = new HashMap<>(); // Convert all Map keys to a List List<String> result = new ArrayList(map.keySet()); // Convert all Map values to a List List<String> result2 = new ArrayList(map.values()); // Java 8, Convert all Map ...
Programiz
programiz.com › java-programming › examples › convert-map-list
Java Program to Convert Map (HashMap) to List
import java.util.*; public class ... "b"); map.put(3, "c"); map.put(4, "d"); map.put(5, "e"); List<Integer> keyList = new ArrayList(map.keySet()); List<String> valueList = new ArrayList(map.values()); System.out.println("Key List: " + keyList); System.out.println("Value ...
Stack Abuse
stackabuse.com › java-convert-map-to-list
Java 8: How to Convert a Map to List
October 10, 2023 - Thankfully, we can easily access the keys and values of a map through the keySet() and values() methods. The keySet() method returns a Set of all the keys, which is to be expected, since keys have to be unique. Due to the flexibility of Java Collections - we can create a List from a Set simply ...
Spring Framework Guru
springframework.guru › home › converting java map to list
Converting Java Map to List - Spring Framework Guru
June 25, 2019 - You use the values() method of Map to convert all the values of Map entries into a List.
Java67
java67.com › 2019 › 12 › how-to-convert-map-to-list-in-java-8.html
3 Examples to convert a Map to List in Java 8 - Example Tutorial | Java67
In reality, it's not really possible to convert a Map to a List because both are different types of data structures. A Map is a collection of key-value pairs while a List contains just elements.
Java67
java67.com › 2015 › 01 › how-to-convert-map-to-list-in-java.html
How to convert a Map to List in Java? HashMap to ArrayList Example | Java67
The Map interface also provides three collection views, which allow a map's contents to be viewed as a set of keys, collection of values, or set of key-value mappings. Now let's understand what is a List in Java, It is also an interface to provide an ordered collection based on an index.
Top answer 1 of 13
1540
List<Value> list = new ArrayList<Value>(map.values());
assuming:
Map<Key,Value> map;
2 of 13
145
The issue here is that Map has two values (a key and value), while a List only has one value (an element).
Therefore, the best that can be done is to either get a List of the keys or the values. (Unless we make a wrapper to hold on to the key/value pair).
Say we have a Map:
Map<String, String> m = new HashMap<String, String>();
m.put("Hello", "World");
m.put("Apple", "3.14");
m.put("Another", "Element");
The keys as a List can be obtained by creating a new ArrayList from a Set returned by the Map.keySet method:
List<String> list = new ArrayList<String>(m.keySet());
While the values as a List can be obtained creating a new ArrayList from a Collection returned by the Map.values method:
List<String> list = new ArrayList<String>(m.values());
The result of getting the List of keys:
Apple Another Hello
The result of getting the List of values:
3.14 Element World
Techie Delight
techiedelight.com › home › java › build a map from a list of keys and values in java
Build a Map from a List of keys and values in Java | Techie Delight
July 7, 2026 - Since a stream is a sequence of elements and not a sequence of key-value pairs, you can’t directly construct a map out of it. You need to specify how to extract keys and values from elements of the stream using the Collectors.toMap() method.
WsCube Tech
wscubetech.com › resources › java › programs › convert-map-to-list
Convert Map (HashMap) to List in Java: 5 Programs
1 month ago - Learn 5 easy ways to convert a Map or HashMap to a List in Java. Explore programs using constructors, entrySet(), lambda expressions, and more. Read now!
Dev.java
dev.java › learn › using-maps-to-store-key-value-pairs
Using Maps to Store Key Value Pairs
Skip Top Navigation Bar · Tutorials · Watch & Listen · FAQ · Oracle University · Your first Java code · Using IDEs · Java Platform Evolution · Using JDK Preview Features · Language Basics · Object Oriented Programming · Generics, Lambda, and Pattern Matching ·
Techie Delight
techiedelight.com › home › java › convert map to a list in java 8 and above
Convert Map to a List in Java 8 and above | Techie Delight
July 7, 2026 - We know that Map.entrySet() returns a set view of the mappings contained in this map. In Java 8, we can easily get a list of key-value pairs by converting it to stream, as shown below:
Top answer 1 of 4
3
List<String> list = map.entrySet()
.stream()
.map(entry -> entry.getKey() + "-" + entry.getValue())
.sorted()
.collect(Collectors.toList());
2 of 4
2
Just a slightly different variant to the other answers. if the insertion/iteration order is important then I'd rather use a LinkedHashMap in the first place as opposed to using a HashMap then sorting it which is actually not always guaranteed to work.
Example:
Map<Integer, String> map = new LinkedHashMap<>();
...
...
...
then stream over the entrySet and collect to a list implementation:
List<String> list = map.entrySet()
.stream()
.map(e -> e.getKey() + "-" + e.getValue())
.collect(Collectors.toList());
How to do in Java
howtodoinjava.com › home › collections framework › java hashmap › java – convert a map to array, list or set
Java - Convert a Map to Array, List or Set
January 11, 2023 - List<Integer> listOfValues = map.values().stream().collect(Collectors.toCollection(ArrayList::new)); Likewise, we can convert Map keys to List using plain Java and Streams.
Baeldung
baeldung.com › home › java › java collections › java map › how to convert list to map in java
How to Convert List to Map in Java | Baeldung
April 4, 2025 - Java Map‘s put() method is implemented so that the latest added value overwrites the previous one with the same key.
Reddit
reddit.com › r/learnjava › how to fetch a list which is a "value" in map?
r/learnjava on Reddit: How to fetch a List which is a "value" in Map?
October 21, 2022 -
Hi folks, I hope you're doing awesome in life. I got stuck in a situation which is -
I've got a map which is of type -
Map<Integer,List<Integer>> m = new HashMap<>();
Now the thing is I want to create a (key,value) in map like -
(Key->Value)
(1->[1,2,3]),
(2 ->[2,3,4]),
(-1->[5,6,7]),
(0->[4])
And I want to add these key value pair in the Map by using the given below statement -
If(m.conatinskey(x)){ m.Put(x,m.get(x).add(any value)); ***** line ****** } else{ List<Integer> temp = new ArrayList<>(); temp.add(any integer value); m.add(temp); }
Now when I'm trying to execute the line statement I'm getting an error stating that my error has been simplified and I need verbose for better explanation but when I'm writing the statement as -
m.get(x).add(any value);
I am not getting any error . Can someone please let me know what's the issue as in my line statement I'm first trying to get the key and at thay key index I'm trying to add the element in the list ?
Top answer 1 of 4
3
the first example will not compile. The second one does not make sure the list exists first. If it doesnt exist at the key then you'll get a NullPointerException. You can enforce adding an empty list if it does not already exist by using computeIfMissing rather than get dict.computeIfMissing(key, k -> new ArrayList<>()).add(value) Which is the equivalent of this in terms of the functionality you care about List list = dict.get(key); if (list == null) { list = new ArrayList<>(); dict.put(key, list); } list.add(value); or the less efficient if (!dict.contains(key)) { dict.put(key, new ArrayList<>()); } List list = dict.get(key); list.add(value); (the latter is less efficient because you are performing two lookups - one in contains and one in get). computeIfAbsent is closer to the second example, but in concurrent implementations also has the benefit of being atomic
2 of 4
2
You don’t need to put again, the list you added is a reference to that list. Technically you could create a new list, add it to the map, then modify the list because you still have a reference to it. It will be modified “in” the map. So just check if the list is there, get it, then modify it.
Javaprogramto
javaprogramto.com › 2020 › 08 › java-8-convert-map-to-list-hashmap-to-arraylist.html
Java 8 – Convert Map to List (HashMap to ArrayList)
August 16, 2020 - package com.javaprogramto.java... ids.forEach(id -> System.out.println(id)); } } ... Use the map.values() method to get all values as Set and pass to the ArrayList constructor....
Top answer 1 of 4
107
Your uniqueRecs has String type of the key. You have to do:
List<String> keys = new ArrayList<>(uniqueRecs.keySet());
or
List<ARecord> values = new ArrayList<>(uniqueRecs.values());
2 of 4
8
What worked for me that i wanted to modify an existing list was:
list.addAll(map.keySet());