import java.util.Map;
import java.util.Optional;
import java.util.HashMap;

class Main {
    public static void main(String[] args) {
        final Map<String, Object> ctx = getAMap();
        System.out.println(ctx);

        // This line succeeds, even though the fully-qualified syntax specifies Integer when attempting to get a String value
        System.out.println(Main.<Integer>getValue(ctx, "STR"));
        System.out.println();

        Main.<Integer>getValue(ctx, "STR");
        // The same code fails when we try to assign "ING" to `Integer a`, not during the cast in `getValue`
        // Integer a = Main.<Integer>getValue(ctx, "STR");
        // System.out.println(a);
        System.out.println();

        Main.<String>getValue(ctx, "INT");
        // This line fails to cast String to Integer during printing, again not during the cast in `getValue`
        // System.out.println(Main.<String>getValue(ctx, "INT"));
        System.out.println();

        // This line prints "true"
        System.out.println(Main.<Foo>getValue(ctx, "BOOL"));
        // but this one fails at compile time, because "Main.Foo cannot be converted to Boolean"
        // System.out.println(Main.<Foo>getValue(ctx, "BOOL") instanceof Boolean);
        System.out.println();

        // This case works consistently
        System.out.println(Main.<String>getValue(ctx, "ABSENT"));
    }

    public static <T> T getValue(Map<String, Object> context, String key) {
        if (context.containsKey(key)) {
            Object obj = context.get(key);
            System.out.println(obj.getClass().getName());
            T cast = (T) obj;
            System.out.println("Cast to " + cast.getClass().getName());
            return cast;
        } else {
             return null;
        }
     }

    public static Map<String, Object> getAMap() {
        Map<String, Object> aMap = new HashMap<String, Object>();
        aMap.put("STR", "ING");
        aMap.put("INT", 1);
        aMap.put("BOOL", true);
        return new HashMap<>(aMap);
    }


    private class Foo {
        public String toString() {
            return "FooFooFoo";
        }
    }
}