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up vote 0 down vote favorite

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...

share|improve this question
    
bird and animal?? –  VD' 1 hour ago
    
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 1 hour ago
    
I want to use the string stored in variable_name as a new variable of type Animal –  user2919740 1 hour ago
    
do you want to instantiate a new Animal and assign it to the field with name 'variable_name' ? –  Totò 1 hour ago
    
assign it to the field with name 'variable_name' –  user2919740 1 hour ago
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2 Answers

up vote 2 down vote accepted

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;
share|improve this answer
1  
In general, reflection isn't worth the trouble. –  Anubian Noob 1 hour ago
1  
I agree, that's why I suggested a map to store objects by name. –  Totò 1 hour ago
    
Actually that's a great idea. –  Anubian Noob 1 hour ago
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up vote 0 down vote

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");
share|improve this answer
    
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(); –  user2919740 1 hour ago
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