Question

Am trying to gives more than one value to a key in a map. I wanted something of this kind to work..
mapp.put(“key1″,”value1”)
mapp.put(“key1″,”value2”).
The first value “value1” is getting over-ridden with “value2”. How to retain both the values? Should I go for any other thing than maps for this to happen?

Answer 1

You can use un map with list. Something like that:

Map<String, List<String>> map = new HashMap<String, List<String>>();

For put a key1 with the first value:

if (!map.containsKey("key1")) {
    map.put("key1", new LinkedList<String>());
}
map.get("key1").add("value1");

For add the second value to key1

map.get("key1").add("value2");

You can have all this in one method

public void add(String key, String value) {
    if (!map.containsKey(key)) {
        map.put(key, new LinkedList<String>());
    }
    map.put(key, value);
}

If you want the values for the key1, you obtain a List

List<String> values = map.get("key1");