Get HashMap with Reflection

Question

public class First {
    public final static Map<String, String> MAP = new HashMap<>();
    static {
        MAP.put("A", "1");
        MAP.put("B", "2");
    }
}

public class Second {
    public static void main(String[] args) {
        Class<?> clazz = Class.forName("First");
        Field field = clazz.getField("MAP");
        Map<String, String> newMap = (HashMap<String, String>) field.get(null); // Obviously doesn't work
    }
}

Pretty much it. I have no trouble getting for example values of String variables, but I'm stuck with this one. Tryed to google it, failed. Also, if possible I'd like to get this Map without instantiating its class.

Answer 1

The only thing you are missing is to handle the exceptions for:

• Class.forName("First");
• clazz.getField("MAP");
• field.get(null);

The code below get the static map field from First class. Here I'm just throwing/propagating the exceptions in the main method but you should handle the exceptions in a try/catch block accordingly.

class First {
  public final static Map<String, String> MAP = new HashMap<>();
  static {
    MAP.put("A", "1");
    MAP.put("B", "2");
  }
}


public class Second {
  public static void main(String[] args) throws IllegalArgumentException, IllegalAccessException,
      ClassNotFoundException, NoSuchFieldException, SecurityException {
    Class<?> clazz = Class.forName("First");
    Field field = clazz.getField("MAP");
    Map<String, String> newMap = (HashMap<String, String>) field.get(null); // Obviously doesn't work
    System.out.println(newMap); //Prints {A=1, B=2}
  }
}