Additional methods for working with associative arrays (maps) appeared in Java 8

putIfAbsent() adds a key-value pair only if the key was missing: 

map.putIfAbsent("a", "Aa");

forEach() takes a function that performs an operation on each element: 

map.forEach((k, v) -> System.out.println(v));

compute() creates or updates the current value with the resulting calculation (it is possible to use the key and the current value): 

map.compute("a", (k, v) -> String.valueOf(k).concat(v)); // ["a", "aAa"]

computeIfPresent() if the key exists, it updates the current value with the one obtained as a result of the calculation (it is possible to use the key and the current value):

map.computeIfPresent("a", (k, v) -> k.concat(v));

computeIfAbsent() if the key is absent, creates it with the value that is calculated (it is possible to use the key):

map.computeIfAbsent("a", k -> "A".concat(k)); //["a","Aa"]

getOrDefault() in the absence of a key, returns the passed default value:

map.getOrDefault("a", "not found");

merge() takes a key, a value, and a function that merges the passed and current values. If there is no value under the given key, then it writes the transferred value there.

map.merge("a", "z", (value, newValue) -> value.concat(newValue)); //["a","Aaz"]

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