Lesson 5 of 9

Arrays and ArrayList

JAVA · inside main

int[] grades = {88, 92, 75};
System.out.println(grades[0]);
System.out.println(grades.length);
int sum = 0;
for (int g : grades) {
    sum += g;
}
System.out.println("Average: " + (double) sum / grades.length);

Output

88
3
Average: 85.0

An array has a fixed size. For a list that grows and shrinks, use ArrayList:

JAVA

import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {
        ArrayList<String> courses = new ArrayList<>();
        courses.add("SQL");
        courses.add("Java");
        courses.add("ERP");
        courses.remove("Java");
        System.out.println(courses);
        System.out.println(courses.size() + " " + courses.get(0));
    }
}

Output

[SQL, ERP]
2 SQL

Watch outIndexes start at 0. Asking for grades[3] in a 3-item array throws ArrayIndexOutOfBoundsException.

Same idea in both languages

Python

courses = ["SQL", "Java"]
courses.append("ERP")
print(len(courses))

Java

ArrayList<String> courses = new ArrayList<>();
courses.add("SQL");
courses.add("Java");
courses.add("ERP");
System.out.println(courses.size());