CODEWITHSUNDEEP
javaarraylist
n00b1990
n00b1990

Reputation: 1249

How can I pass a dataType as an argument to create an ArrayList of this type?

Let's say I have something like:

public void do(DataType type) {
    ArrayList<DataType> list = new ArrayList<DataType>();
    doStuff();
}

In some cases I want to create an arrayList of another type by passing the type as a parameter, how can I do this in Java?

Upvotes: 2

Views: 715

Answers (5)

Praba
Praba

Reputation: 1381

Are you looking for something like this?

public static <T> List<T> doSomething(Class<T> clazz){
    ArrayList<T> testList = new ArrayList<T>();
    return testList;
    // more code
}

and you can invoke this like :

List<Integer> intList = doSomething(Integer.class);
intList.add(1);
List<String> stringList = doSomething(String.class);
stringList.add("test");

and if you want to restrict the type of Class you need, you could use T extends youDataType. If what @subhash has explained is not the one you are looking for, and if what @zoyd explains is true, then i believe this could be of some use.

Upvotes: 1

Zoyd
Zoyd

Reputation: 3559

Java doesn't allow to pass class types as method parameters. As far as I know, the closest you can get is this :

import java.util.*;

class MyClass<T> {

    public void stuff() {
        ArrayList<T> list = new ArrayList<T>();
        //doStuff();
    }

}

class Test {        
    public static void main(String args[]) {
        (new MyClass<String>()).stuff();
        (new MyClass<Integer>()).stuff();
    }
}

So you would need to instanciate the class each time you need it.

Upvotes: 1

Ashot Karakhanyan
Ashot Karakhanyan

Reputation: 2830

More universal approach is the following:

public <T extends IDataType> void doSomething(T type) {
    ArrayList<T> list = new ArrayList<T>();
    doStuff();
}

where: DataType implements IDataType

In this case you can use any type which implements IDataType

Upvotes: 1

Karolis.sh
Karolis.sh

Reputation: 1738

I assume you want something like this:

public static <T>List<T> makeList(T t) {
    List<T> list = new ArrayList<T>();
    // doStuff();
    return list;
}

And usage of makeList function:

makeList("String list").add("new String"); // ok
makeList("String list").add(5);            // compile error

Upvotes: 1

subash
subash

Reputation: 3140

try this..

    public <T> void stuff(T type){
        ArrayList<T> arrayList = new ArrayList<T>();
        doStuff();
    }

generics may be helpfull you if you want to create sigle object that represent it, but when you want a simple private attribute the easy way is this.

Upvotes: 6

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