C#のenumにフィールド・メソッドを定義したいとき【JavaからC#へ】 ref: https://qiita.com/lilacs/items/167a73fbbfedf83eb51a

appState.cs

public enum AppState
{
    Active, Paused, Exit
}
public static class AppStateExt
{
    private static Dictionary<AppState, string> viewStrDictionary = new Dictionary<AppState, string>()
    {
        {AppState.Active,"アクティブ" },
        {AppState.Paused,"ポーズ" },
        {AppState.Exit,"イグジット" }
    };
    public static string viewStr(this AppState state)       //<-　拡張メソッド
    {
        return viewStrDictionary[state];
    }

}
class Program
{
    public static void Main(string[] args)
    {
        Console.WriteLine(AppState.Active.viewStr());       // <- インスタンスメソッドのように呼び出せる
    }
}

appState.java

enum AppState
{
    Active("アクティブ"), Paused("ポーズ"), Exit("イグジット");

    public final String viewStr;
    AppState(String viewStr){
        this.viewStr = viewStr;
    }
}
class Main
{
    public static void main (String[] args) throws java.lang.Exception
    {
        System.out.println(AppState.Active.viewStr);    // <- enumのフィールド呼び出し
    }
}

フィールド増やした場合.cs

    private static Dictionary<AppState, string> viewStrDictionary = new Dictionary<AppState, string>()
    {
        {AppState.Active,"アクティブ" },
        {AppState.Paused,"ポーズ" },
        {AppState.Exit,"イグジット" }
    };
    private static Dictionary<AppState, int> waitTimeDictionary = new Dictionary<AppState, int>()    //<-　追加したフィールド
    {
        {AppState.Active,10 },
        {AppState.Paused,20 },
        {AppState.Exit,30 }
    };
    //（以下、フィールドの数だけ続く。。。）

自分でEnum定義.cs

public class AppState
{
    //フィールド一覧
    public readonly string viewStr;
    public readonly int waitTime;
    //コンストラクタ
    private AppState(string viewStr, int waitTime)
    {
        this.viewStr = viewStr;
        this.waitTime = waitTime;
    }
    //メソッド
    public string getViewStr()
    {
        return this.viewStr;
    }

    // 参照用インスタンス
    public static readonly AppState Active = new AppState("アクティブ", 10);
    public static readonly AppState Paused = new AppState("ポーズ", 20);
    public static readonly AppState Exit = new AppState("イグジット", 30);
}

class Program
{
    public static void Main(string[] args)
    {
        Console.WriteLine(AppState.Active.viewStr);         //<- フィールド呼び出し
        Console.WriteLine(AppState.Active.getViewStr());    //<- メソッド呼び出し
    }
}

自分でEnum定義する方法.cs

public class AppState
{
    //フィールド一覧
    public readonly string viewStr;
    public readonly int waitTime;
    //コンストラクタ
    private AppState(string viewStr, int waitTime)
    {
        this.viewStr = viewStr;
        this.waitTime = waitTime;
    }
    //メソッド
    public string getViewStr()
    {
        return this.viewStr;
    }

    // 参照用インスタンス
    public static readonly AppState Active = new AppState("アクティブ", 10);
    public static readonly AppState Paused = new AppState("ポーズ", 20);
    public static readonly AppState Exit = new AppState("イグジット", 30);
}