Create a variable having name stored in a string variable

Question

Let's say:

I have a Class Animal and I want to create an instance of that class by the name "bird". "bird" is stored in a String.

How to do that?

String variable_name = "bird";

I want to use the string in variable_name as an Animal's instance.

Animal bird = new Animal();

Thanks...

It's not exactly clear what you're asking. Do you want to have a field inside Animal that when accessed would return "bird", or do you want to have the actual instance name of the Animal be based on some value in a String, in this case bird? — aruisdante
– aruisdante, Commented Apr 25, 2014 at 1:27
I want to use the string stored in variable_name as a new variable of type Animal — user2919740
– user2919740, Commented Apr 25, 2014 at 1:36
do you want to instantiate a new Animal and assign it to the field with name 'variable_name' ? — Totò
– Totò, Commented Apr 25, 2014 at 1:37
why do you want to use the string to determine the variable name? the name of a local variable doesn't affect code outside of the block where it is declared. — NamshubWriter
– NamshubWriter, Commented Apr 25, 2014 at 1:57

Totò · Accepted Answer · 2014-04-25 01:50:17Z

2

You can do this with the reflection

public class DynamicSetTest {

    private Animal animal1 = null;
    private Animal animal2 = null;
    private Animal animal3 = null;

    public Animal getAnimal1() {
        return animal1;
    }
    public Animal getAnimal2() {
        return animal2;
    }
    public Animal getAnimal3() {
        return animal3;
    }

    public void setField(String name, Animal value) throws Exception {
            Field field = this.getClass().getDeclaredField(name);
            field.set(this, value);
    }

    public static void main(String[] args) throws Exception {
        DynamicSetTest t = new DynamicSetTest();
        Animal anAnimal = new Animal();
        t.setField("animal3", anAnimal);
        assert t.getAnimal3() == anAnimal;
    }
}

Note that you have a field for each possible name. You also have to handle the case if the variable doesn't exist.

I'm wondering if you instead want to use a Map and add objects using that name like

Map<String, Animal> animals = new HashMap<String, Animal>();
animals.put("animal3", anAnimal);
assert animals.get("animal3") == anAnimal;

answered Apr 25, 2014 at 1:50

Totò

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3 Comments

Anubian Noob Over a year ago

In general, reflection isn't worth the trouble.

Totò Over a year ago

I agree, that's why I suggested a map to store objects by name.

Anubian Noob Over a year ago

Actually that's a great idea.

Anubian Noob · Accepted Answer · 2014-04-25 01:24:11Z

0

Add name as a field in Animal and ask for it in the constructor.

class Animal {

    String name;

    public Animal(String name) {
        this.name = name;
    }
}

Then when you construct an animal use:

Animal bird = new Animal("bird");
Animal deer = new Animal("deer");
Animal wumpus = new Animal("wumpus");

answered Apr 25, 2014 at 1:24

Anubian Noob

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1 Comment

user2919740 Over a year ago

e.g: Animal deer = new Animal("deer"); In your example, you've written Animal deer. but I want to use the string stored in variable_name as a new variable of type Animal Something like: String variable_name = "deer"; Animal variable_name= new Animal();

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