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HashMap savedStuff = new HashMap();
savedStuff.put("symbol", this.symbol); //this is a string
savedStuff.put("index", this.index); //this is an int
gives me the warning:
HashMap is a raw type. References to generic type HashMap<K,V> should be parameterized
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Using HashMap makes sense only when unique keys are available for the data we want to store. We should use it when searching for items based on a key and quick access time is an important requirement. We should avoid using HashMap when it is important to maintain the same order of items in a collection.
In HashMap (or HashTable ) you can only have UNIQUE KEYS, you cannot have different values assigned to the same key. In your code you attempt put 2 different values with the same key: map.
Disadvantages of HashMapPotential of collision when 2 distinct keys generate the same hashCode() value worse the performance of the hashMap. Occasionally HashMaprequires resizing when the original size of HashMap buckets are full.
This is simple code for use of hashmap. There i will use key as integer and value as string type. Map is very useful when our functionality works on key and values pairs. Below is a simple example of use hashmap. I hope it is very useful for all.
public class CreateHashMap {
public static void main(String[] args) {
Map<Integer,String> map = new HashMap<Integer,String>();
/*
* Associates the specified value with the specified key in
this map (optional operation). If the map previously
contained a mapping for the key, the old value is
replaced by the specified value
*/
map.put(1,"ankush");
map.put(2, "amit");
map.put(3,"shivam");
map.put(4,"ankit");
map.put(5, "yogesh");
//print hashmap
System.out.println("HashMap = "+map);
}
}
Reference : create and use of map
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