Search if specified key and value exists

Question

I am working with hashmap datastructure in java. I have some data in which each entry(value) has a group(key). Now i am storing this data in hashmap as follows

HashMap<Integer, String> map = new HashMap<Integer, String>();
map.put(1, "value1");
map.put(1, "value2");
map.put(2, "value3");
map.put(2, "value4");
map.put(3, "value5");
map.put(3, "value6");
map.put(3, "value7");

now I want to search if entry (with key=3 and value="value6") exists in map or not. Is there any specific method to call? or is there and other way to do it?

Answer 1

You can not keep multiple entry against same key in a map. If your map previously contained a mapping for the key, the old value is replaced. You need

Map<Integer,List<String>> map = new HashMap<>();
                                          ^^^^^
                                     (Diamond operator)

Where you could save List of string against same key. and you can get the value by map#get

List<String> str = map.get(3);

Answer 2

You can make use of Guava Multimap (API docs)

Its stores the multiple values against one key. For your case ,

Multimap<Integer,String> myMultimap = ArrayListMultimap.create();
myMultimap .put(1, "value1");
myMultimap .put(1, "value2");
myMultimap .put(2, "value3");
myMultimap .put(2, "value4");
myMultimap .put(3, "value5");
myMultimap .put(3, "value6");
myMultimap .put(3, "value7");

This will create the data structure for you

now I want to search if entry (with key=3 and value="value6") exists in map or not. Is there any specific method to call? or is there and other way to do it?

For searching use multimap#containsEntry(key,value), which return boolean result based on the result

therefore,

myMultimap.containsEntry(3,"value6")

which will return true

Answer 3

In broad terms: map.get(key) will retrieve either the value at this key location, or null if it doesn't exist.

Second, you're actually crushing your values. Maps only ever store one value per key. If you want to store multiple values, consider using another collection as the value, which you can add values into later.

Here's some sample code:

//Declaration - change List to Set if duplicates are annoying
Map<Integer, List<String>> map = new HashMap<>();

//Usage - if the list is empty at the key, new one up.  Append the value afterwards.
Integer key = Integer.valueOf(1);
List<String> values = map.get(key);
if(key == null) {
     values = new ArrayList<>();
}
values.add("word");
map.put(key, values);

Determining the existence of a value at a particular key becomes easy, too:

public boolean inMap(Map<Integer, List<String>> map, Integer key, String value) {
    final List<String> values = map.get(key);
    return values != null && values.contains(value);
}