use variable type to define another variable type

Question

Im trying to use the type of one variable to define the type on another I know i could just put all the types in an enum then use ordinal with a switch/case to select but i'm wondering if theres an easier way.

Heres a small example:

public void loadRotation(TetrominoType type) {
TetrominoType new = new type.class();
}

TetroiminoType type = new RedTetro();
this.loadRotation(type);

RedTetro obviously extends TetrminoType

I know this won't work but hopefully from it you understand what i'm trying to do.

Assuming an object is passed, see the Object.getClass() method and follow the links from there -- which would allow reflection utilization. Other options include passing in a Class<...> or using a "factory pattern". — user166390
– user166390, Commented Oct 17, 2011 at 1:11

Brian Roach · Accepted Answer · 2011-10-17 01:17:40Z

1

Reflection is the answer.

If you're talking about a class that has a zero argument constructor, it's quite straight forward:

MyClass c = new MyClass();
MyClass c2 = c.getClass().newInstance();

If you need to use a constructor that takes arguments you have to extract the Constructor you need and use that. Oracle provides a tutorial here:

http://download.oracle.com/javase/tutorial/reflect/member/ctorInstance.html

answered Oct 17, 2011 at 1:17

Brian Roach

77k12 gold badges140 silver badges164 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

mgm8870 · Accepted Answer · 2011-10-17 01:05:30Z

1

you could use the instanceof evaluator:

public class MainClass {
  public static void main(String[] a) {

    String s = "Hello";
    if (s instanceof java.lang.String) {
      System.out.println("is a String");
    }
}
}

answered Oct 17, 2011 at 1:05

mgm8870

6791 gold badge5 silver badges10 bronze badges

2 Comments

Diesal11 Over a year ago

But theres 7 different types, i was trying to avoid writing a condition statement for each class

user166390 Over a year ago

This also doesn't really answer the fundamental question: how to pass a type-constructor to a method?

Community · Accepted Answer · 2017-05-23 11:55:40Z

1

You can use Java reflection to rewrite the type based on the type of the variable you have.

You can find out more here http://java.sun.com/developer/technicalArticles/ALT/Reflection/ and a similar problem here Dynamic variables with given type

It should be a case of utilising the base class of your type too set a basic type and then using reflection to create the variable with the new type.

edited May 23, 2017 at 11:55

CommunityBot

11 silver badge

answered Oct 17, 2011 at 1:09

redache

212 bronze badges

Comments

user207421 · Accepted Answer · 2011-10-17 01:22:41Z

0

You need to look up the Factory design pattern.

answered Oct 17, 2011 at 1:22

user207421

312k45 gold badges324 silver badges493 bronze badges

Collectives™ on Stack Overflow

use variable type to define another variable type

4 Answers 4

Comments

2 Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related