ArrayList<>

An array list is a pre-defined collection parameterized by the type of data it contains.

import java.util.*;

public class ArrayListDemos {

public static void test1() {
ArrayList<Integer> list = new ArrayList<Integer>();
for(int i = 0; i < 10; i++) {
list.add(i * i);
}
System.out.println(list);
}

public static void test2() {
ArrayList<String> list = new ArrayList<String>();
for(int i = 0; i < 10; i++) {
list.add("String" + i);
}
System.out.println(list);
}

public static void test3() {
ArrayList<String> heroes = new ArrayList<String>();
ArrayList<String> moreHeroes = new ArrayList<String>();
heroes.add("Superman");
heroes.add("Batman");
heroes.add("Roidman");
heroes.add("Spiderman");
moreHeroes.add("Wonderwoman");
moreHeroes.add("Catwoman");
System.out.println(heroes);
System.out.println(moreHeroes);
heroes.addAll(moreHeroes);
System.out.println(heroes);
heroes.remove("Roidman");
System.out.println(heroes);
heroes.set(2, "Dark Knight");
System.out.println(heroes);
for(int i = 0; i < heroes.size(); i++) {
System.out.println(heroes.get(i));
}

}


public static void main(String[] args) {
test1();
test2();
test3();
}


}

Program Output

[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
[String0, String1, String2, String3, String4, String5, String6, String7, String8, String9]
[Superman, Batman, Roidman, Spiderman]
[Wonderwoman, Catwoman]
[Superman, Batman, Roidman, Spiderman, Wonderwoman, Catwoman]
[Superman, Batman, Spiderman, Wonderwoman, Catwoman]
[Superman, Batman, Dark Knight, Wonderwoman, Catwoman]
Superman
Batman
Dark Knight
Wonderwoman
Catwoman

The Enhanced For-Loop

The enhanced for loop is the cool way to traverse an array list. Here's the general form:

for(ElementType var: someList) {
// in here var will take on every value in someList
}

For example:

ArrayList<String> heroes = new ArrayList<String>();
heroes.add("Superman");
heroes.add("Batman");
heroes.add("Spiderman");
heroes.add("Wonderwoman");
heroes.add("Catwoman");

for(String hero: heroes) {
System.out.println("Hero: " + hero);
}