2 similar java enums and a method who decide from which enum should the value be chosen

user_3771470 0
Viewed 352

I want to implement a method who decide from what java enum to get a specific value. For example:

public enum Credentials1 {
    USERNAME("user"),
    PASSWORD("pass");
}
public enum Credentials2 {
    USERNAME("user"),
    PASSWORD("pass");
}

and then, in another class I want a generic method to decide, based on another param, what enum should I use to get the correct user. Something like:

public String decide(here I should pass something?) {
    switch (myParam) {
        case "1":
            return Credentials1.USERNAME;
        case "2":
            return Credentials2.USERNAME;
    }
    return "";
}

Can this be achievable, because I didn't succeed? And think that besides USERNAME and PASSWORD I will have a lot of constants in those enums.

enums java string
2 Answers

Create an interface Credentials with the following method:

public interace Credentials {

    public String value();
}

Make these enums to implement an interface with a common method returning the value. Below is Credentials1. The Credentials2 is implemented analogically.

public enum Credentials1 implements Credentials {

    USERNAME("user"),
    PASSWORD("pass");

    private String value;

    Credentials1(String value) {
        this.value= value;
    }

    @Override
    public String value() {
        return this.str;
    }
}

Here you pass the correct enum for the further processing:

public String decide(Credentials credentials) {
     return credentials.value();
}

A sample usage is:

String string = this.decide(Credentials1.USERNAME);
user_37649650

First create a method that returns the desired enumeration class:

public Class<? extends Enum<?>> getEnum(int param)
{
  // Determine enumeration class based on specified parameter
  switch (param)
  {
    case 1:
      return (Enum1.class);
    case 2:
      return (Enum2.class);
    default:
      return (null);
  }

} // getEnum

Then create a method that returns the desired instance:

public Object getEnumInstance(Class<? extends Enum<?>> clazz,
                              String                   name)
  throws Exception
{
  // Determine the 'valueOf()' method that creates an instance from a string
  // Every enumeration class has a static valueOf() method that expects a String as a parameter
  Method value_of_method;
  value_of_method = clazz.getDeclaredMethod("valueOf", String.class);

  // Get and return instance
  return (value_of_method.invoke(null, name));

} // getEnumInstance

Next, create a method that returns the value of the specified enum:

public String getEnumValue(Object enum_instance)
  throws Exception
{
  // Determine the 'getValue()' method of this enumeration instance
  // At least, I suppose the method is called like that in your enumeration classes
  // It doesn't want parameters and returns a String
  Method get_value_method;
  get_value_method = enum_instance.getClass().getMethod("getValue");

  // Return value of the enumeration instance
  return ((String)get_value_method.invoke(enum_instance));

} // getEnumValue

Finally, create a method that combines the whole stuff:

public String decide(int    param,
                     String enum_instance_name)
  throws Exception
{
  // Get correct enumeration class
  Class<? extends Enum<?>> enum_class;
  enum_class = getEnum(param);

  // Get correct instance
  Object enum_instance;
  enum_instance = getEnumInstance(enum_class, enum_instance_name);

  // Return its value
  return (getEnumValue(enum_instance));

} // decide

Now we can finally do what we have to do:

public void run()
  throws Exception
{
  // Get password of 2nd enum
  String result;
  result = decide(2, "PASSWORD");
  System.out.println(result);

  // Or username of 1st enum
  result = decide(1, "USERNAME");
  System.out.println(result);

} // run
user_33756700
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