Java Language Maps Using Default Methods of Map from Java 8
Example
Examples of using Default Methods introduced in Java 8 in Map interface
- Using getOrDefault
Returns the value mapped to the key, or if the key is not present, returns the default value
Map<Integer, String> map = new HashMap<>();
map.put(1, "First element");
map.get(1); // => First element
map.get(2); // => null
map.getOrDefault(2, "Default element"); // => Default element
- Using forEach
Allows to perform the operation specified in the 'action' on each Map Entry
Map<Integer, String> map = new HashMap<Integer, String>();
map.put(1, "one");
map.put(2, "two");
map.put(3, "three");
map.forEach((key, value) -> System.out.println("Key: "+key+ " :: Value: "+value));
// Key: 1 :: Value: one
// Key: 2 :: Value: two
// Key: 3 :: Value: three
- Using replaceAll
Will replace with new-value only if key is present
Map<String, Integer> map = new HashMap<String, Integer>();
map.put("john", 20);
map.put("paul", 30);
map.put("peter", 40);
map.replaceAll((key,value)->value+10); //{john=30, paul=40, peter=50}
- Using putIfAbsent
Key-Value pair is added to the map, if the key is not present or mapped to null
Map<String, Integer> map = new HashMap<String, Integer>();
map.put("john", 20);
map.put("paul", 30);
map.put("peter", 40);
map.putIfAbsent("kelly", 50); //{john=20, paul=30, peter=40, kelly=50}
-
Using remove
Removes the key only if its associated with the given value
Map<String, Integer> map = new HashMap<String, Integer>(); map.put("john", 20); map.put("paul", 30); map.put("peter", 40); map.remove("peter",40); //{john=30, paul=40} -
Using replace
If the key is present then the value is replaced by new-value. If the key is not present, does nothing.
Map<String, Integer> map = new HashMap<String, Integer>();
map.put("john", 20);
map.put("paul", 30);
map.put("peter", 40);
map.replace("peter",50); //{john=20, paul=30, peter=50}
map.replace("jack",60); //{john=20, paul=30, peter=50}
- Using computeIfAbsent
This method adds an entry in the Map. the key is specified in the function and the value is the result of the application of the mapping function
Map<String, Integer> map = new HashMap<String, Integer>();
map.put("john", 20);
map.put("paul", 30);
map.put("peter", 40);
map.computeIfAbsent("kelly", k->map.get("john")+10); //{john=20, paul=30, peter=40, kelly=30}
map.computeIfAbsent("peter", k->map.get("john")+10); //{john=20, paul=30, peter=40, kelly=30} //peter already present
- Using computeIfPresent
This method adds an entry or modifies an existing entry in the Map. Does nothing if an entry with that key is not present
Map<String, Integer> map = new HashMap<String, Integer>();
map.put("john", 20);
map.put("paul", 30);
map.put("peter", 40);
map.computeIfPresent("kelly", (k,v)->v+10); //{john=20, paul=30, peter=40} //kelly not present
map.computeIfPresent("peter", (k,v)->v+10); //{john=20, paul=30, peter=50} // peter present, so increase the value
- Using compute
This method replaces the value of a key by the newly computed value
Map<String, Integer> map = new HashMap<String, Integer>();
map.put("john", 20);
map.put("paul", 30);
map.put("peter", 40);
map.compute("peter", (k,v)->v+50); //{john=20, paul=30, peter=90} //Increase the value
- Using merge
Adds the key-value pair to the map, if key is not present or value for the key is null Replaces the value with the newly computed value, if the key is present Key is removed from the map , if new value computed is null
Map<String, Integer> map = new HashMap<String, Integer>();
map.put("john", 20);
map.put("paul", 30);
map.put("peter", 40);
//Adds the key-value pair to the map, if key is not present or value for the key is null
map.merge("kelly", 50 , (k,v)->map.get("john")+10); // {john=20, paul=30, peter=40, kelly=50}
//Replaces the value with the newly computed value, if the key is present
map.merge("peter", 50 , (k,v)->map.get("john")+10); //{john=20, paul=30, peter=30, kelly=50}
//Key is removed from the map , if new value computed is null
map.merge("peter", 30 , (k,v)->map.get("nancy")); //{john=20, paul=30, kelly=50}
