在Java中使用HashMaps

Question

Basically I'm making this Java program in BlueJ, in which the player is in the world of The Lord of the Rings. I created separate packages for weapons, items etc. I have a class Main outside all the packages(in the main body of the project screen). In there, I tried something.

public static void test()throws Exception{
        System.out.println("There is a brass sword and an iron sword. Which do you want?");
        Scanner in = new Scanner(System.in);
        String s = in.next();
        HashMap options = new HashMap();
        options.put("brass", new Sword());
        options.put("iron", new Sword());
        Sword k = options.get(s);
}

I want the above method to return a Sword object to me. This does not work, unfortunately. Any help....?

Answer 1

Just use the parametrized type HashMap , declare the HashMap as

HashMap<String, Sword> options = new HashMap<String, Sword>();

I want the above method to return a Sword object to me.

Then change the method return type and add a return to it:

public static Sword test()throws Exception{
        System.out.println("There is a brass sword and an iron sword. Which do you want?");
        Scanner in = new Scanner(System.in);
        String s = in.next();
        HashMap<String, Sword> options = new HashMap<String, Sword>();
        options.put("brass", new Sword());
        options.put("iron", new Sword());
        Sword k = options.get(s);
        return k;
}

Answer 2

Use following code:

public static Sword test()throws Exception{
    System.out.println("There is a brass sword and an iron sword. Which do you want?");
    Scanner in = new Scanner(System.in);
    String s = in.next();
    HashMap<String, Sword> options = new HashMap<String, Sword>();
    options.put("brass", new Sword());
    options.put("iron", new Sword());
    return options.get(s);
}

Answer 3

如果您希望您的方法返回Sword对象，则应将public static void test()更改为public static Sword test()并在方法结束时调用return sword

Answer 4

The default hashMap accepts two generic types HashMap<Object,Object> which represents HashMap<Key,Value> with your code you will have to cast the options.get(s) to Sword but with that you don't use the power of Generics so recommend the @BackSlash's answer since you won't need casting.

More on Generics: http://www.tutorialspoint.com/java/java_generics.htm