英文:
How to create a HashMap with methods as values?
问题
我正在编写一个能够接收多个指令的小程序。每个指令都应该调用不同的方法。我在考虑是否有一种方法可以将所有这些方法放入一个HashMap中，并通过获取与指令键配对的值来直接调用它们，而不是使用if语句，这样可以使事情变得更简单。但据我所了解，这似乎是不可能的，因为在Java中，方法不被视为对象。尽管如此，了解是否有一种方法来实现这一点仍然是有教育意义的。
英文:
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.
答案1
得分: 2
Methods 不是对象（至少大多数情况下不是），但有一个与您想要的相匹配的概念：函数式接口，它被定义为具有正好一个抽象方法的接口。两个开箱即用的候选接口是 Runnable，它不接受参数，以及 Consumer，它接受一个参数，如果您想要传入某种输入（如 Scanner），可能是最佳选择。（如果您还想要可配置的输出，带有 Scanner 和 PrintWriter 的 BiConsumer 可能适合。）
Java 有一个称为 方法引用 的便利功能，可以自动将方法转换为函数式接口的实例。组合在一起，可能是这样的：
Map<String, Consumer<Scanner>> commands = new HashMap<>();
...
commands.put("foo", someCommand::go); // 其中 someCommand 是一个具有 go(Scanner) 方法的变量
commands.put("bar", new OtherCommand());
commands.put("hello", unused -> { System.out.println("Hello!"); });
...
String commandName = scanner.next();
commands.get(commandName).accept(scanner);
英文:
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);
答案2
得分: 0
这不是一个好主意，将方法作为哈希映射的值并不满足shell命令复杂的场景，也许你可以使用Runnable对象作为值。
另一个解决方案是，你可以使用Spring Shell。
@ShellMethod("commandName")
public String doSomething(String param) {
return String.format("Hi %s", param);
}
英文:
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);
}
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