Create an array of classes and then instantiate objects from them

Question

I want to create an array of classes, then iterate through that array and instantiate objects from each of the classes in that array.

I tried the following:

Class[] classes = {Gummy.class, Chocolate.class, Lollipop.class};

for (Class candyClass : classes) {
    for (int i = 0; i < r.nextInt(5); i++) {
        candyList.add(new candyClass(r.nextDouble() + 0.1 * 20));
    }
}

And I got this error:

CandyTester.java:19: error: cannot find symbol
                candyList.add(new candyClass(r.nextDouble() + 0.1 * 20));
                                  ^
  symbol:   class candyClass
  location: class CandyTester
1 error

I don't really know where to proceed from here because I'm not too sure how java class relates to objects.

Kluddizz · Accepted Answer · 2020-03-16 10:10:17Z

1

Use the method newInstance(args), which instantiates a new object of your class using a specific constructor.

Object candy = candyClass.getDeclaredConstructor(Double.class).newInstance(r.nextDouble() + 0.1 * 20);
candyList.add((Candy) candy);

edited Mar 16, 2020 at 10:10

answered Mar 16, 2020 at 2:41

Kluddizz

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6 Comments

Max Gordon Over a year ago

I tried that and it said: CandyTester.java:19: error: method newInstance in class Class<T> cannot be applied to given types and the reason was actual and formal argument lists differ in length

Kluddizz Over a year ago

Try candyClass.getDeclaredConstructor(Double.class).newInstance(...). This should work.

Max Gordon Over a year ago

I tried that and I got a different error this time: CandyTester.java:19: error: incompatible types: Object cannot be converted to Candy and it also said Note: CandyTester.java uses unchecked or unsafe operations.

Kluddizz Over a year ago

All the classes must be a subclass of Candy, if you want to store it in a List<Candy>. Using Reflection will give you that kind of note, because using methods of this package is unsafe.

Max Gordon Over a year ago

Thank you for your help!! I casted it to Candy to avoid that error.

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