I can't initialize multiple classes of similar type (child and parent) within a function-CodePudding

I have a parent class , 'Scene' and multiple classes that inherit it. I want to take an 'id' value and initialize a certain class, but have a problem with duplicate types if a switch / if statements are used.

  if (sceneType == 1) {
     Scene scene = new Scene(jsonScene.getInt("id"));
  } else if (sceneType == 2) {
       EndingScene scene = new EndingScene(jsonScene.getInt("id"));
    } else if (sceneType == 3) {
      InformationScene scene = new InformationScene(jsonScene.getInt("id"));
    }  else if (sceneType == 4) {
      AnswerScene scene = new AnswerScene(jsonScene.getInt("id"));  
    } else if (sceneType == 5) {
      ActionScene scene = new ActionScene(jsonScene.getInt("id"));  
    } 
    
  scene.doSomething();

scene.doSomething throws error as in the scope outside the if statements, scene has not been initialized.

Scene scene;
  
  if (sceneType == 1) {
     Scene scene = new Scene(jsonScene.getInt("id"));
  } else if (sceneType == 2) {
       EndingScene scene = new EndingScene(jsonScene.getInt("id"));
    } else if (sceneType == 3) {
      InformationScene scene = new InformationScene(jsonScene.getInt("id"));
    }  else if (sceneType == 4) {
      AnswerScene scene = new AnswerScene(jsonScene.getInt("id"));  
    } else if (sceneType == 5) {
      ActionScene scene = new ActionScene(jsonScene.getInt("id"));  
    } 
    
  scene.doSomething();

Alternatively if I define scene in the scope of my function, initializing the different types of scene are duplicate local variables.

I also have the problem when a general function that's return type is specific to parent object, but if I want it to return the object type passed into it, rather than the parent by default.

CodePudding user response：

When you declare a variable in a method, you can't re-declare it.

This code should works :

Scene scene;

if (sceneType == 1) {
 scene = new Scene(jsonScene.getInt("id"));
} else if (sceneType == 2) {
   EndingScene scene = new EndingScene(jsonScene.getInt("id"));
} else if (sceneType == 3) {
  InformationScene scene = new InformationScene(jsonScene.getInt("id"));
}  else if (sceneType == 4) {
  AnswerScene scene = new AnswerScene(jsonScene.getInt("id"));  
} else if (sceneType == 5) {
  ActionScene scene = new ActionScene(jsonScene.getInt("id"));  
} 

scene.doSomething();

CodePudding user response：

It is possible to use Dictionary<TKey, TValue> in C# or HashTable in Java to avoid multiple if else statements.

Let me show an example via C#.

Your base and derived classes:

public class Scene 
{
    public string Name { get; set; }
}

public class AnswerScene : Scene { }

public class InformationScene : Scene { }

and scene types:

public enum SceneType
{
    Base, Answer, Information
}

And factory which creates an instance of Scene by SceneType:

public class SceneToType
{
    public Dictionary<SceneType, Scene> SceneByType { get; private set; } = new()
    {
        { SceneType.Information, new InformationScene() },
        { SceneType.Answer, new AnswerScene() },
        { SceneType.Base, new Scene() }
    };
}

and then you can create objects by calling a method:

Scene GetInstance(SceneType sceneType) 
{
    return new SceneToType().SceneByType[sceneType];
}