Java Collections Framework - List Interface Method Examples
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Over the next few weeks, I’m going to go over the Java Collections Framework and just so examples for each method. This week being the first week I’ll start with what is probably the most commonly used collections: the List.
My goal is to publish one of these each Monday. So feel free to tune out Mondays if programming isn’t your thing. Or if it is, feel free to be sure to tune in Mondays.
If there’s a Monday that happens to coincide with one of my normal monthly posts (which, as of right now, is just my monthly blog stats reports that I do on the twentieth) then I’ll either post it a day early, a day late… Or, get this, I might skip a week.
But the next time the 20th falls on Monday is in September - three months or 17 weeks from now - so I might be finished by then anyway.
I plan to focus on Java 8, since (I feel, so citation needed) that is the most used Java version in production.
As of Java 8, List has 32 separate methods. I’ve used every one below except for spliterator, parallelStream, and stream.
The code, in all its glory:
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
public class ListSample {
public static void main(String[] args) {
// Just some variables to reuse
boolean changed;
boolean isTrue;
String string;
int index;
List<String> list = new ArrayList<>();
// list = []
changed = list.add("Hello");
// changed = true
// list = [Hello]
list.add(1, "Hi");
// list = [Hello, Hi]
changed = list.addAll(Arrays.asList("Bonjour", "Hola"));
// changed = true
// list = [Hello, Hi, Bonjour, Hola]
changed = list.addAll(0, Arrays.asList("Ciao", "Hallo"));
// changed = true
// list = [Ciao, Hallo, Hello, Hi, Bonjour, Hola]
changed = list.addAll(list);
// changed = true
// list = [Ciao, Hallo, Hello, Hi, Bonjour, Hola, Ciao, Hallo, Hello, Hi, Bonjour, Hola]
isTrue = list.contains("Hello");
// isTrue = true
isTrue = list.contains("Goodbye");
// isTrue = false
isTrue = list.containsAll(list);
// isTrue = true
isTrue = list.containsAll(Arrays.asList("Hi"));
// isTrue = true
isTrue = list.containsAll(Arrays.asList("Hi, Goodbye"));
// isTrue = false
isTrue = list.equals(list);
// isTrue = true
string = list.get(0);
// string = Ciao
string = list.get(list.size() - 1);
// string = Hola
int hash = list.hashCode();
// hash = 1027746517
index = list.indexOf("Hello");
// index = 2
index = list.indexOf("Goodbye");
// index = -1
index = list.lastIndexOf("Hello");
// index = 8
index = list.lastIndexOf("Goodbye");
// index = -1
string = list.remove(0);
// string = Ciao
// list = [Hallo, Hello, Hi, Bonjour, Hola, Ciao, Hallo, Hello, Hi, Bonjour, Hola]
changed = list.remove("Hello");
// changed = true
// list = [Hallo, Hi, Bonjour, Hola, Ciao, Hallo, Hello, Hi, Bonjour, Hola]
changed = list.remove("Goodbye");
// changed = false
// list = [Hallo, Hi, Bonjour, Hola, Ciao, Hallo, Hello, Hi, Bonjour, Hola]
changed = list.removeAll(Arrays.asList("Ciao", "Hallo"));
// changed = true
// list = [Hi, Bonjour, Hola, Hello, Hi, Bonjour, Hola]
list.replaceAll(String::toUpperCase);
// list = [HI, BONJOUR, HOLA, HELLO, HI, BONJOUR, HOLA]
changed = list.retainAll(list);
// changed = false
// list = [HI, BONJOUR, HOLA, HELLO, HI, BONJOUR, HOLA]
changed = list.retainAll(Arrays.asList("HELLO", "HI"));
// changed = true
// list = [HI, HELLO, HI]
string = list.set(0, "Goodbye");
// string = HI
// list = [Goodbye, HELLO, HI]
int size = list.size();
// size = 3
list.sort(Comparator.naturalOrder());
// list = [Goodbye, HELLO, HI]
list.sort(Comparator.reverseOrder());
// list = [HI, HELLO, Goodbye]
List<String> sublist = list.subList(0, 2);
// sublist = [HI, HELLO]
Object[] objects = list.toArray();
// objects = [Ljava.lang.Object;@4f023edb
String[] strings = list.toArray(new String[0]);
// strings = [Ljava.lang.String;@3a71f4dd
list.clear();
// list = []
list.addAll(Arrays.asList("Hallo", "Hello", "Hi", "Bonjour", "Hola", "Ciao", "Hallo", "Hello", "Hi", "Bonjour", "Hola"));
// list = [Hallo, Hello, Hi, Bonjour, Hola, Ciao, Hallo, Hello, Hi, Bonjour, Hola]
System.out.println(list);
//list.forEach(System.out::println);
// just prints each string; if strings weren't immutable I could change them here
list.removeIf(s -> s.startsWith("H"));
// list = [Bonjour, Ciao, Bonjour]
System.out.println(list);
changed = list.retainAll(Arrays.asList("Goodbye"));
// changed = true
// list = []
}
}
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