Printing HashMap In Java

Question

I have a HashMap:

private HashMap example = new HashMap();

Now I would lik

Answer 1

Assuming you have a Map<KeyType, ValueType>, you can print it like this:

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

Answer 2

If the map holds a collection as value, the other answers require additional effort to convert them as strings, such as Arrays.deepToString(value.toArray()) (if its a map of list values), etc.

I faced these issues quite often and came across the generic function to print all objects using ObjectMappers. This is quite handy at all the places, especially during experimenting things, and I would recommend you to choose this way.

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

public static String convertObjectAsString(Object object) {
    String s = "";
    ObjectMapper om = new ObjectMapper();
    try {
        om.enable(SerializationFeature.INDENT_OUTPUT);
        s = om.writeValueAsString(object);
    } catch (Exception e) {
        log.error("error converting object to string - " + e);
    }
    return s;
}

Answer 3

A simple way to see the key value pairs:

Map<String, Integer> map = new HashMap<>();
map.put("a", 1);
map.put("b", 2);
System.out.println(Arrays.asList(map)); // method 1
System.out.println(Collections.singletonList(map)); // method 2

Both method 1 and method 2 output this:

[{b=2, a=1}]

Answer 4

Worth mentioning Java 8 approach, using BiConsumer and lambda functions:

BiConsumer<TypeKey, TypeValue> consumer = (o1, o2) -> 
           System.out.println(o1 + ", " + o2);

example.forEach(consumer);

Assuming that you've overridden toString method of the two types if needed.

Answer 5

For me this simple one line worked well:

Arrays.toString(map.entrySet().toArray())

Answer 6

I did it using String map (if you're working with String Map).

for (Object obj : dados.entrySet()) {
    Map.Entry<String, String> entry = (Map.Entry) obj;
    System.out.print("Key: " + entry.getKey());
    System.out.println(", Value: " + entry.getValue());
}