It is a specialized implementation of the Map interface. It is used to store <key, value> pairs. Hashing technique is used in HashMap implementation.
A few important facts about HashMap are as follows:
- It allows duplicate values.
- It is not synchronized.
- It is an ordered collection.
- It allows a null key, but only once.
Hierarchy of HashMap class
It extends AbstractMap and implements Map, Clonable, Srializable interfaces in Java.
Source code of Item.java
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package com.t4b.test;
public class Item {
String name;
int id;
double price;
public Item(String name, int id, double price) {
super();
this.name = name;
this.id = id;
this.price = price;
}
@Override
public String toString() {
return "Item [name=" + name + ", id=" + id + ", price=" + price + "]";
}
}
Source code of TestMain.java
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package com.t4b.test;
import java.util.HashMap;
import java.util.Map;
public class TestMain {
public static void main(String[] args) {
HashMap<Integer, Item> map = new HashMap<Integer, Item>();
map.put(1, new Item("Apple", 1, 150.0));
map.put(2, new Item("Grape", 2, 250.0));
map.put(3, new Item("Mango", 3, 10));
map.put(2, new Item("Pine Apple", 4, 100));
for (Map.Entry item : map.entrySet()) {
System.out.println(item.getKey() + " : " + item.getValue());
}
}
}
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