Java HashMap
You learned from the previous chapter, that Arrays store items as an ordered collection, and you have to access them with an index number (int type). A HashMap however, store items in 'key/value' pairs, and you can access them by an index of another type (e.g. a String).
One object is used as a key (index) to another object (value). It can store different types: String keys and Integer values, or the same type, like: String keys and String values:
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Example
Create a HashMap object called capitalCities that will store Stringkeys and Stringvalues:
Add Items
The HashMapGenerate ssh key mac osx. class has many useful methods. For example, to add items to it, use the put() method:
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Access an Item
To access a value in the HashMap, use the get() method and refer to its key:
Example
Remove an Item
To remove an item, use the remove() method and refer to the key:
To remove all items, use the clear() method:
Example
HashMap Size
Generate Keys For Hashmap C Classes For Integers 1
To find out how many items there are, use the size method:
Example
Loop Through a HashMap
Loop through the items of a HashMap with a for-each loop.
Note: Use the keySet() method if you only want the keys, and use the values() method if you only want the values:
Example
Other Types
Keys and values in a HashMap are actually objects. In the examples above, we used objects of type 'String'. Remember that a String in Java is an object (not a primitive type). To use other types, such as int, you must specify an equivalent wrapper class: Integer. For other primitive types, use: Boolean for boolean, Character for char, Double for double, etc:
Example
Create a HashMap object called people that will store Stringkeys and Integervalues:
Generic hashmap with String as key and Integer as value
Related examples in the same category
| 1. | Iterate through the values of Java HashMap example |
| 2. | Get Synchronized Map from Java HashMap example |
| 3. | Check if a particular key exists in Java HashMap example |
| 4. | Check if a particular value exists in Java HashMap example |
| 5. | Get Set view of Keys from Java HashMap example |
| 6. | Get Size of Java HashMap |
| 7. | Remove all values from Java HashMap example |
| 8. | Remove value from Java HashMap |
| 9. | Create Java Hashtable from HashMap |
| 10. | Sort an HashMap based on the keys |
| 11. | For keys of a map |
| 12. | For values of a map |
| 13. | For both the keys and values of a map |
| 14. | Storing Primitive Types in a Collection |
| 15. | Creating a Copy of a Collection: the objects are not cloned. |
| 16. | Use Iterator to loop through the map key set |
| 17. | Get key set and value set from map and use Iterator to loop through them |
| 18. | Clones a map |
| 19. | Hash map for counting references to Object keys. |
| 20. | Extended Version of java.util.HashMap that provides an extended get method accpeting a default value. |
| 21. | Compact HashMap |
| 22. | This class wraps a HashMap and provides methods by which key objects can be associated with 'counting' values. |
| 23. | This extension of HashMap support duplicate keys |
| 24. | Concurrent Hopscotch HashMap |