Java Generics Selective Return Value

Question

I struggled with this for a while and have not yet found an answer. As a result, my brain got a little confused, so forgive me if I make a dumb mistake.

I am trying to implement a typed INI analyzer that will parse this file:

[section1] <int>intkey=0 <float>floatkey=0.0 <str>stringkey=test [section2] <float>x=1.0 <float>y=1.0 <float>z=0.0 

In doing so, I have a central class called Config , which handles the basic read and write operations. One of the Config methods is called get(String section, String key) , which ideally should return a value corresponding to the required key pair pair, for example:

 Config cfg = new Config("test.ini"); cfg.get("section2", "x"); // 1.0, not "1.0" or some Object that technically represents the float cfg.get("section1", "intkey"); // 0 cfg.get("section1", "strkey"); // "test" 

I am currently using enum to handle converting String to various types using the abstract method, overridden by different types:

 enum Type { INTEGER ("int") { public Object parse(String value) { try { return Integer.parseInt(value); } catch (NumberFormatException e) { return null; } } }, FLOAT ("float") { public Object parse(String value) { try { return Float.parseFloat(value); } catch (NumberFormatException e) { return null; } } }, STRING ("str") { public Object parse(String value) { return value; } }; public final String name; Type(String name) { this.name = name; } private static HashMap<String, Type> configMap = generateConfigMap(); private static HashMap<String, Type> generateConfigMap() { HashMap<String, Type> map = new HashMap<String, Type>(); for (Type type : Type.values()) map.put(type.name, type); return map; } public static Type get(String name) { return configMap.get(name); } abstract public Object parse(String value); } 

Unfortunately, parse(String value) returns an object, and when transferring from Config , a listing or similar is required, and ideally it will be self-sufficient.

If I am going to do it completely wrong, and there is a more flexible or easier way to encode it, please let me know. I am open to suggestions. Although I would like to know if there is a way to do this. Maybe with generics ...?

Note. I know that I am missing imports and the like. This is not what I am posting here.

Answer 1

Here is the thing. If the code calling config.get() does not know what type to expect, you will not be able to return anything except the object, since the call code does not know what to expect. Of course you have to quit.

Now, if you want to create Config in such a way that the calling user knows what type he requested, what makes it a little easier. The easiest way is to do something like this:

 public class Config { public int getInt(String a, String b) { return ((Integer)get(a, b)).intValue(); } } 

But as long as the caller does not know what to expect, you really won’t gain anything to avoid the cast.

Answer 2

If you want to return the type of an object depending on what you get, you can do this:

 public <T extends MyObject> T myMethod(Class<T> type) { return type.cast(myObj); }