How can I call a method on each element of a List?

Sandro Munda picture Sandro Munda · Aug 28, 2011 · Viewed 76.6k times · Source

Suppose that I have a list of cars :

public class Car {
    private String brand;
    private String name;
    private String color;

    public Car() { // ...  }

    public getName() { return name; }
    // ...
}

// Suppose that I have already init the list of car
List<Car> cars = //...
List<String> names = new ArrayList<String>();


for (Car c : cars ) {
    names.add(c.getName());
}

How can I shorten the code above ? In a nutshell, How can I call a method on each element of a List ?

For example, in Python :

[car.name for car in cars]

Answer

aaiezza picture aaiezza · Dec 19, 2013

Java 8 will (hopefully) have some form of lambda expression, which will make code like this more feasible. (Whether there'll be anything like list comprehensions is another matter.)

Your wish has been granted!

---EDIT---
lol as if on cue: forEach()

Definitely check this out.

For your question specifically, it becomes the folowing:

// Suppose that I have already init the list of car
List<Car> cars = //...
List<String> names = new ArrayList<String>();

// LAMBDA EXPRESSION
cars.forEach( (car) -> names.add(car.getName()) );

It's really quite incredible what they've done here. I'm excited to see this used in the future.

---EDIT---
I should have seen this sooner but I can't resist but to post about it.

The Stream functionality added in jdk8 allows for the map method.

// Suppose that I have already init the list of car
List<Car> cars = //...

// LAMBDA EXPRESSION
List<String> names = cars.stream().map( car -> car.getName() ).collect( Collectors.toList() );

Even more concise would be to use Java 8's method references (oracle doc).

List<String> names = cars.stream().map( Car::getName ).collect( Collectors.toList() );