Timesgroups Interviews questions: Iterate hashmap in java

You can use the following different ways.....

1: Iterating HashMaps over entries using For-Each loop.

Use this if you need both map keys and values in the loop.

Map<String, String> map = new HashMap<String, String>();
for (Map.Entry<String, String> entry : map.entrySet()) {
    System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());
}
-------------------------------------------------------------------
2. Filterating over keys or values using for-each loop.......

If you need only keys or values from the map, you can iterate over keySet or values instead of entrySet.

Map<Integer, Integer> map = new HashMap<Integer, Integer>();
//iterating over keys only
for (Integer key : map.keySet()) {
    System.out.println("Key = " + key);
}

//iterating over values only
for (Integer value : map.values()) {
    System.out.println("Value = " + value);
}
-----------------------------------------------------------
3.: Iterating using Iterator......with the help of entrySet() method

Using Generics:

Map<Integer, Integer> map = new HashMap<Integer, Integer>();
Iterator<Map.Entry<Integer, Integer>> entries = map.entrySet().iterator();   //entrySet() returns set
while (entries.hasNext()) {
    Map.Entry<Integer, Integer> entry = entries.next();
    System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());
}

Without Generics:

Map map = new HashMap();
Iterator entries = map.entrySet().iterator();        //entrySet() returns set
while (entries.hasNext()) {
    Map.Entry entry = (Map.Entry) entries.next(); 
    Integer key = (Integer)entry.getKey();
    Integer value = (Integer)entry.getValue();
    System.out.println("Key = " + key + ", Value = " + value);
}

-------------------------------------------------------------------------------

4: Iterating over keys and then searching for values with the help of keys(Not good).

Map<Integer, Integer> map = new HashMap<Integer, Integer>();
for (Integer key : map.keySet()) {
    Integer value = map.get(key);
    System.out.println("Key = " + key + ", Value = " + value);
}

Popular posts from this blog

Can not connect to git using ssh (Permissions 0644 for '/root/.ssh/id_rsa' are too open.

Upload file on Google cloud storage using Java servlet on google app engine

Session timeout interceptor in struts 2