Object Instantiation from User Input

[LegoWizardCode]

How can I create an object that is the type a user has passed in? Here is an example of what I mean:

import java.util.*;
public class ObjInit {
  public Object initObjOfType(String type) {
    Object obj;
    if(type.equals(/*Type of Object*/)) {
      obj = new /*Type of Object*/();
    }
    return obj;
  }
}

A problem I encountered when attempting this is that the type of object is casted to an object, and I do not want that. I want to make it so no casting is needed so it is all automated.

[WindLother]

You can use the reflection API.
There is a good example here:

Using Java Reflection

[WindLother]

Being more specific by adapting your example:

import java.util.*;

public class ObjInit {
  public Object initObjOfType(String type) {
    Object obj = null;
    try {
      Class<?> clazz = Class.forName(type);
      obj = clazz.getDeclaredConstructor().newInstance();
    } catch (Exception e) {
      e.printStackTrace();
    }
    return obj;
  }
}

[LegoWizardCode]

I am not sure I am using this correctly. I used your code, and It gives me an error, saying myObject can not use nextLine() because it is of type Object.

Object myObject = o.initObjOfType("Scanner");
myObject.nextLine();

[Idkwhttph]

Hello, @LegoWizardCode! Welcome to the forums!

If you want to create an object of the type specified by a user in Java, you can use reflection to accomplish this. Here is an example implementation of your initObjOfType method using reflection:

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

public class Main {
  public Object initObjOfType(String type) throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
    Class<?> clazz = Class.forName(type);
    Constructor<?> constructor = clazz.getConstructor();
    return constructor.newInstance();
  }

  public static void main(String[] args) {
    // your code here
  }
}

}

}

Yes and again, if this does not work im gonna

[LegoWizardCode]

This works, but is there a way to make it so it returns the object as the initialized type rather than type object? (Without casting)

[WindLother]

Since the type is being determined at runtime, it’s not possible for the method to return a value of that type without casting.

Buuut, you can use Java’s generics to achieve something similar

Like this:

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

public class Main {
  public <T> T initObjOfType(Class<T> clazz) 
    throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
      
    Constructor<T> constructor = clazz.getConstructor();
    return constructor.newInstance();
  }

  public static void main(String[] args) {
    try {
      String str = new Main().initObjOfType(String.class);
      // Use str...
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}

[LegoWizardCode]

This is the solution. Thank you.