How to get values and keys from HashMap?

Question

I'm writing a simple edit text in Java. When the user opens it, a file will be opened in JTabbedPane. I did the following to save the files opened:

HashMap<String, Tab> hash = new HashMap<String, Tab>();

Where Tab will receive the values, such as: File file, JTextArea container, JTabbedPane tab.

I have a class called Tab:

public Tab(File file, JTextArea container, JTabbedPane tab)
{
    this.file = file;
    this.container = container;
    this.tab = tab;
    tab.add(file.getName(), container);
    readFile();
}

Now, in this SaveFile class, I need get the Tab values stored in the HashMap. How can I do that?

Already ? It's always so, negative the topic. – Apr 26 '13 at 23:57 — , Apr 26 '13 at 23:57

Bohemian · Accepted Answer · 2017-02-27T09:25:43.247

To get all the values from a map:

for (Tab tab : hash.values()) {
    // do something with tab
}

To get all the entries from a map:

for ( Map.Entry<String, Tab> entry : hash.entrySet()) {
    String key = entry.getKey();
    Tab tab = entry.getValue();
    // do something with key and/or tab
}

Java 8 update:

To process all values:

hash.values().forEach(tab -> /* do something with tab */);

To process all entries:

hash.forEach((key, tab) -> /* do something with key and tab */);

Prabhu · Answer 2 · 2017-07-24T03:00:23.403

Map is internally made up of Map.Entry objects. Each Entry contains key and value. To get key and value from the entry you use accessor and modifier methods.

If you want to get values with given key, use get() method and to insert value, use put() method.

#Define and initialize map;
Map map = new HashMap();
map.put("USA",1)
map.put("Japan",3)
map.put("China",2)
map.put("India",5)
map.put("Germany",4)

map.get("Germany") // returns 4

If you want to get the set of keys from map, you can use keySet() method

Set keys = map.keySet();
System.out.println("All keys are: " + keys);
// To get all key: value
for(String key: keys){
    System.out.println(key + ": " + map.get(key));
}

Generally, To get all keys and values from the map, you have to follow the sequence in the following order:

Convert Hashmap to MapSet to get set of entries in Map with entryset() method.:
Set st = map.entrySet();
Get the iterator of this set:
Iterator it = st.iterator();
Get Map.Entry from the iterator:
Map.Entry entry = it.next();
use getKey() and getValue() methods of the Map.Entry to get keys and values.

// Now access it
Set st = (Set) map.entrySet();
Iterator it = st.iterator();
while(it.hasNext()){
    Map.Entry entry = mapIterator.next();
    System.out.print(entry.getKey() + " : " + entry.getValue());
}

In short, use iterator directly in for

for(Map.Entry entry:map.entrySet()){
    System.out.print(entry.getKey() + " : " + entry.getValue());
}

score 13 · Answer 3 · answered Apr 27 '13 at 00:10

13

You give 1 Dollar, it gives you a cheese burger. You give the String and it gives you the Tab. Use the GET method of HashMap to get what you want.

HashMap.get("String");

answered Apr 27 '13 at 00:10

user2245180

161
6

3

Shouldn't it be `HashMapObj.get("String");` ? – Hritik Jun 23 '17 at 16:57
2

You give 1 US dollar in 2022 and you get no burger ;-) – Andrei Drynov May 12 '22 at 17:50

score 4 · Answer 4 · answered Feb 13 '19 at 15:35

To get values and keys you could just use the methods values() and keySet() of HashMap

public static List getValues(Map map) {
    return new ArrayList(map.values());
}

public static List getKeys(Map map) {
    return new ArrayList(map.keySet());
}

score 3 · Answer 5 · edited Nov 19 '17 at 12:56

3

for (Map.Entry<String, Tab> entry : hash.entrySet()) {
    String key = entry.getKey();
    Tab tab = entry.getValue();
    // do something with key and/or tab
}

Works like a charm.

edited Nov 19 '17 at 12:56

Rob

26,989
16
82
98

answered Nov 19 '17 at 12:53

Gama_aide

61
4

score 3 · Answer 6 · answered Dec 26 '18 at 09:04

3

It will work with hash.get("key"); Where key is your key for getting the value from Map

answered Dec 26 '18 at 09:04

Narendra raghuwanshi

74
5

Answer brings nothing new to the table, other answers already explain this and much more. – Andrejs Dec 26 '18 at 09:26

score 2 · Answer 7 · answered Apr 26 '13 at 23:57

2

Use the 'string' key of the hashmap, to access its value which is your tab class.

Tab mytab = hash.get("your_string_key_used_to_insert");

answered Apr 26 '13 at 23:57

vishakvkt

864
6
7

score 2 · Answer 8 · answered Jun 24 '14 at 17:17

2

You could use iterator to do that:

For keys:

for (Iterator <tab> itr= hash.keySet().iterator(); itr.hasNext();) {
    // use itr.next() to get the key value
}

You can use iterator similarly with values.

answered Jun 24 '14 at 17:17

bruhhhhh

121
5

score 1 · Answer 9 · answered Jan 30 '17 at 18:46

1

With java8 streaming API:

List values = map.entrySet().stream().map(Map.Entry::getValue).collect(Collectors.toList());

answered Jan 30 '17 at 18:46

javabrew

306
4
7

5

That train wreck is the same as just `map.values()` – Bohemian Feb 27 '17 at 09:27

score 0 · Answer 10 · answered Sep 11 '16 at 03:35

0

You have to follow the following sequence of opeartions:

Convert Map to MapSet with map.entrySet();
Get the iterator with Mapset.iterator();
Get Map.Entry with iterator.next();
use Entry.getKey() and Entry.getValue()

# define Map
for (Map.Entry entry: map.entrySet)
    System.out.println(entry.getKey() + entry.getValue);

answered Sep 11 '16 at 03:35

Hary Bakta

499
4
5

6

You copied my answer – Prabhu Sep 11 '16 at 03:46

score 0 · Answer 11 · answered Aug 17 '21 at 14:58

Using java 8 feature:

    map.forEach((key, value) -> System.out.println(key + " " + value));

Using Map.Entry you can print like this:

 for (Map.Entry<KeyType, ValueType> entry : map.entrySet()) 
 {
     System.out.println(entry.getKey()+" : "+entry.getValue());
 }

How to get values and keys from HashMap?

11 Answers11

Java 8 update:

Linked