The computeIfAbsent() in Java computes a given value by using a provided operation function.
Method signature:
The signature for computeIfAbsent() is shown below:
public V computeIfAbsent(K key, Function<? super K, ? extends V> Function)
Methods parameters and return type:
Parameter: It takes a key and a function as a parameter. We perform an operation given in a function on a value of a given key.
Return type: It returns a value of a specific key or null if the mapping is null.
Throws: It throws ConcurrentModificationException.
Example 1:
Here we have computed the 5th value in the hashmap by passing a key and a function in which two values are multiplied.
Source code:
public class Example1 {
public static void main(String[] args) {
// create a HashMap and add some values
HashMap<String, Integer> map = new HashMap<>();
map.put("1", 100);
map.put("2", 200);
map.put("3", 300);
map.put("4", 400);
System.out.println("HashMap: " + map.toString());
map.computeIfAbsent("5", k -> 5 * 25);
System.out.println("Updated HashMap: "+ map);
}
}
Output:
run:
HashMap: {1=100, 2=200, 3=300, 4=400}
Updated HashMap: {1=100, 2=200, 3=300, 4=400, 5=125}
BUILD SUCCESSFUL (total time: 1 second)Example 2:
In this example, we have used string values. We have computed a new string on a key “4.” We have tried again to compute a new string on the 4th key, but as it is already present, so it will not compute again.
Source code:
public class Example2 {
public static void main(String[] args)
{
// create a HashMap and add some values
HashMap<Integer, String> nameMap = new HashMap<>();
nameMap.put(1, "Ali");
nameMap.put(2, "Sara");
nameMap.put(3, "Virat");
System.out.println("HashMap: "+ nameMap.toString());
nameMap.computeIfAbsent(4, k -> "Sameer");
nameMap.computeIfAbsent(4, k -> "Salman");
System.out.println("Updated HashMap: " + nameMap);
}
}
Output:
run:
HashMap: {1=Ali, 2=Sara, 3=Virat}
Updated HashMap: {1=Ali, 2=Sara, 3=Virat, 4=Sameer}
BUILD SUCCESSFUL (total time: 1 second)
References:
