Print all key/value pairs in a Java ConcurrentHashMap
Solution 1
I tested your code and works properly. I've added a small demo with another way to print all the data in the map:
ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<String, Integer>();
map.put("A", 1);
map.put("B", 2);
map.put("C", 3);
for (String key : map.keySet()) {
System.out.println(key + " " + map.get(key));
}
for (Map.Entry<String, Integer> entry : map.entrySet()) {
String key = entry.getKey().toString();
Integer value = entry.getValue();
System.out.println("key, " + key + " value " + value);
}
Solution 2
The HashMap has forEach
as part of its structure. You can use that with a lambda expression to print out the contents in a one liner such as:
map.forEach((k,v)-> System.out.println(k+", "+v));
or
map.forEach((k,v)-> System.out.println("key: "+k+", value: "+v));
Solution 3
You can do something like
Iterator iterator = map.keySet().iterator();
while (iterator.hasNext()) {
String key = iterator.next().toString();
Integer value = map.get(key);
System.out.println(key + " " + value);
}
Here 'map' is your concurrent HashMap.
Solution 4
//best and simple way to show keys and values
//initialize map
Map<Integer, String> map = new HashMap<Integer, String>();
//Add some values
map.put(1, "Hi");
map.put(2, "Hello");
// iterate map using entryset in for loop
for(Entry<Integer, String> entry : map.entrySet())
{ //print keys and values
System.out.println(entry.getKey() + " : " +entry.getValue());
}
//Result :
1 : Hi
2 : Hello
DanGordon
Updated on April 24, 2020Comments
-
DanGordon about 4 years
I am trying to simply print all key/value pair(s) in a ConcurrentHashMap.
I found this code online that I thought would do it, but it seems to be getting information about the buckets/hashcode. Actually to be honest the output it quite strange, its possible my program is incorrect, but I first want to make sure this part is what I want to be using.
for (Entry<StringBuilder, Integer> entry : wordCountMap.entrySet()) { String key = entry.getKey().toString(); Integer value = entry.getValue(); System.out.println("key, " + key + " value " + value); }
This gives output for about 10 different keys, with counts that seem to be the sum of the number of total inserts into the map.
-
Daniël Knippers about 10 yearsTo be fair, he already has the loop you give as an answer (using
entrySet()
,getKey()
,getValue()
). You just squeeze it on 1 line :) -
DanGordon about 10 yearsDoes it matter that I am using StringBuilder?
-
DanGordon about 10 yearsI've changed my map to <Integer [], Integer>. When I do println, I get something like this back: @2d51e135 How do I get the actual value?
-
DanGordon about 6 yearsIf you are using Java 8, I suggest using Rick Il Grande's answer below. It is concise and utilizes the
forEach
available to collections in Java 8.