Understanding Java HashMaps

What are Java HashMaps?

Java HashMap is a class which is used to perform operations such as inserting, deleting and locating elements in a map. We create a map, where we pass two kinds of values which are ‘key’ and ‘value’.

While using HashMaps, values will be put in HashMap and whenever the user retrieves a value, the key will be used in order to use the value.

The map is an interface that maps keys to the elements. Maps are unsorted and unordered. They allow one null key and multiple null values. The values are stored in key and value. One key or multiple values could be null in the entire HashMap. A key can be any object.

There are several methods available in HashMap

• Object put(Object key, Object value)
• Enumeration keys() – it will fetch keys
• Enumeration elements() – it will fetch elements
• Object get(Object keys) – pass the key and get the value associated with it
• Boolean contains key(Object key) – used for checking whether a key is present in HashMap or not
• Boolean contains Value(Object key) – pass the key
• Object remove(Object key) – pass the key and remove the object
• Int size() – for using size
• String to String() – for converting into string

There are corresponding values for each key where values can be null in the HashMap also.

Creation of HashMap.

HashMap hashmap = new HashMap();

Putting elements

hashmap.put(“Ankita”, 9634.58);

hashmap.put(“Vishal”, 1283.48);

hashmap.put(“Gurinder”, 1478.10);

hashmap.put(“Krishna”, 199.11);

Here, we pass key and the value.

Displaying the value – Get an iterator

Iterator iterator = hashmap.entrySet().iterator();

Here, the values are present in the set so we use entrySet.

Along with the line:

While(iterator.hasNext()){

Map.Entry entry=(Map.Entry) iterator.next();

System.out.print(entry.getKey()+”:”);

System.out.printIn(entry.getValue());

}

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