CODEWITHSUNDEEP
javaoophashmap
random math student
random math student

Reputation: 77

How to create a HashMap with methods as values?

I am working a small program which can receive several commands. Each of these commands should cause different methods to run. I was thinking that if there were a way to put all the methods into a HashMap and invoke them directly by getting the value paired with the command Key instead of using if statements, it could make things much simpler but as far as I understand this is not possible since methods aren't treated as objects in Java. Still, it will be educative to find out if there is a way to do this.

Upvotes: 0

Views: 853

Answers (2)

mou wang
mou wang

Reputation: 1

This is not a good idea, make methods as hashmap value don't satisfied shell command complex scene, maybe you can use Runnable Object as value.

Another solution, you can use Spring Shell.

@ShellMethod("commandName")
public String doSomething(String param) {
    return String.format("Hi %s", param);
}

Upvotes: 0

chrylis -cautiouslyoptimistic-
chrylis -cautiouslyoptimistic-

Reputation: 77196

Methods aren't objects (at least mostly not), but there is a concept that matches what you want: the functional interface, which is defined as an interface that has exactly one abstract method. Two out-of-the-box candidates are Runnable, which takes no parameters, and Consumer, which takes a single parameter and might be the best option if you want to pass in some kind of input (like a Scanner). (If you also want a configurable output, BiConsumer taking a Scanner and a PrintWriter might be suitable.)

Java has a convenience feature called method references that can automatically transform a method into an instance of a functional interface. Put together, it might look like this:

Map<String, Consumer<Scanner>> commands = new HashMap<>();
...
commands.put("foo", someCommand::go); // where someCommand is a variable with a go(Scanner) method
commands.put("bar", new OtherCommand());
commands.put("hello", unused -> { System.out.println("Hello!"); });
...
String commandName = scanner.next();
commands.get(commandName).accept(scanner);

Upvotes: 2

Related Questions