如何根据用户输入创建新对象？

Question

I am not sure what the proper terminology for this is but, I am trying to figure out how I could create new instances of an object based on a users input.

Let's say I have 5 different classes of object and I will only need a total of 5 objects from all or some of the classes, I might have more than 1 of a certain class and none of another. what could I write that would create a new instance of all or some of these objects?

Furthermore, I would need to have the new objects fields be set to specific parameters without the users input and I would need to have an ArrayList created at the same time.

Here is an example of 1 such object and arraylist I might need to be generated based on user input with these exact fields:

ArrayList<Item> rangerInv0 = new ArrayList<Item>();    
Ranger rangerObj0 = new Ranger("Ranger", 100, 4, 10, rangerInv0);

Is there a way I could do this? What would this be called?

Also, I am looking to avoid a situation like this

if (resp == 1){
  if (rangerCount == 0){
      ArrayList<Item> rangerInv0 = new ArrayList<Item>();    
      Ranger rangerObj0 = new Ranger("Ranger", 100, 4, 10, rangerInv0);

      rangerObj0.pickUp(mh1000);
      rangerObj0.pickUp(s1000);
      rangerObj0.pickUp(t1000);

      rangerObj0.equip(mh1000);
      rangerObj0.equip(s1000);
      rangerObj0.equip(t1000);

      playerUnits.add(rangerObj0);
      playerUnitsCount++;
      rangerCount++;
      }
      else if (rangerCount == 1){
      ArrayList<Item> rangerInv1 = new ArrayList<Item>();    
      Ranger rangerObj1 = new Ranger("Ranger", 100, 4, 10, rangerInv1);

      rangerObj1.pickUp(mh1000);
      rangerObj1.pickUp(s1000);
      rangerObj1.pickUp(t1000);

      rangerObj1.equip(mh1000);
      rangerObj1.equip(s1000);
      rangerObj1.equip(t1000);

      playerUnits.add(rangerObj1);
      playerUnitsCount++;
      rangerCount++;
      }
      else if (rangerCount == 2){
      ArrayList<Item> rangerInv2 = new ArrayList<Item>();    
      Ranger rangerObj2 = new Ranger("Ranger", 100, 4, 10, rangerInv2);

      rangerObj2.pickUp(mh1000);
      rangerObj2.pickUp(s1000);
      rangerObj2.pickUp(t1000);

      rangerObj2.equip(mh1000);
      rangerObj2.equip(s1000);
      rangerObj2.equip(t1000);

      playerUnits.add(rangerObj2);
      playerUnitsCount++;
      rangerCount++;
      }
    } 

is there a way I could update my object and ArrayList names via variables or some kind of counter?

it would be cool if I could do something like this but so far I cannot find a way to make this work:

int rangerCount = 0;
String rangerInvNum = ("rangerInv" + rangerCount);
String rangerObjNum = ("rangerObj" + rangerCount);

ArrayList<Item> rangerInvNum = new ArrayList<Item>();    
Ranger rangerObjNum = new Ranger("Ranger", 100, 4, 10, rangerInvNum);

Answer 1

What you need is to use proper design pattern for this kind of logic and what you can to choose here seems to be Builder , Factory or Strategy (the last one in this case would be kind of factory actually)

The simpliest solution like this would look like

public interface Item {}

public class Ranger implements Item {
    // ...
}

// ...

public class CommonCreationProperties {
    // All the fields user can popularne
}

public class ItemFactory{
    public Item createItem(CommonProperties properties)
        if(isRanger(properties)) {
            return new Ranger(properties.getType(), ...); // Event better introduce builder here
        } else if(is...) {
             return ...
        }
    }

    private boolean isRanger(CommonProperties properties) {
        return "Ranger".equals(properties.getType());
    }

    // ...
}

Of course providing some special type field to recognize what type of Item user provided is one of the options - you can implement some another mechanism - the only thing is that using such approach your items should have some common interface like Item and many implementations depends on what types of items you need

Answer 2

You could try a switch case:

String className = "user input here"
switch(className) {
  case "Ranger": {
    Ranger myRanger = new Ranger();
    ArrayList<Item> rangerInv0 = new ArrayList<Item>();
    break;
    }
  case "otherClass": {
    OtherClass myObj = new OtherClass();
    ArrayList<Item> otherClassInv0 = new ArrayList<Item>();
    break;
    }
case "....": {
    // ....
    break;
    }
  default: {
    // print error message, end program, ...
    }
}

Answer 3

• This will help to you
• you don't need to create Object types and One by one variables and you can use some generics like I have implemented

public class Ranger<E> {

    private  String objectName;
    private Type val1;
    private Type val2;
    private Type val3; // here you can set any kind of typs ex, int,string 
    private E[] rangerInv0; // you can set any kind of array 

    public Ranger(String objectName, Type val1, Type val2, Type val3, E[] rangerInv0) {
        super();
        this.objectName = objectName;
        this.val1 = val1;
        this.val2 = val2;
        this.val3 = val3;
        this.rangerInv0 = rangerInv0;
    }