ConsumeSingleton.java

public class ConsumeSingleton {
  
  public ConsumeSingleton() {
    HttpClient._.call(...);
    HttpClient.get.call(...);
    HttpClient.INSTANCE.call(...);
  }
  
}

HttpClient__.java

public enum HttpClient {
   _;
  
   private HttpClient() {
     // setup
   }
  
  public int call(String method, String url) { 
     // ...
    return 200;
  }
  
}

HttpClient_get.java

public enum HttpClient {
   get;
  
   private HttpClient() {
     // setup
   }
  
  public int call(String method, String url) { 
     // ...
    return 200;
  }
  
}

HttpClient_INSTANCE.java

public enum HttpClient {
   INSTANCE;
  
   private HttpClient() {
     // setup
   }
  
  public int call(String method, String url) { 
     // ...
    return 200;
  }
  
}