List<E>

Learn generic lists with List<E>.

The List<E> interface

List<E> is the core interface of the Java collection framework. E is a type parameter that tells what the list holds. List<String> holds only strings, List<Integer> only integers.

The most common concrete implementation is ArrayList: List<String> names = new ArrayList<>();. The diamond <> on the right copies the left type. A List keeps insertion order; get(0) returns the first element.

List methods

Common list methods: add(e) appends, get(i) returns the element at index, set(i, e) replaces it, remove(i) deletes it, size() returns the count.

Example: names.add("Ayşe"); names.add("Alex"); String first = names.get(0);. Indices start at zero; names.get(0) returns the first element. indexOf(e) finds an element index or returns -1.

Exercise Build a name list

Declare List<String> names = new ArrayList<>();. Add three names with names.add("Ayşe");, names.add("Alex"); and names.add("Mehmet");. Print the first name with System.out.println(names.get(0)); and the count with System.out.println(names.size());.

Show example solution

import java.util.List;
import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>();
        names.add("Ayşe");
        names.add("Alex");
        names.add("Mehmet");
        System.out.println(names.get(0));
        System.out.println(names.size());
    }
}

Test yourself

Complete the list declaration

List<String> names = new ____<>();

Show answer

List<String> names = new ArrayList<>();

Match the List methods

add(e)

Appends an element
get(i)

Returns the element at index
set(i, e)

Replaces the element at index
size()

Returns the element count
What does names.get(0) return?
- The length of the list
- The first added element
- The last added element
- The type parameter of the list
Show answer

The first added element — get(0) returns the first element; List keeps insertion order.

Next lesson: Map<K,V>

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