✦ CodingBat ➽ https://codingbat.com/java

✦ LeetCode ➽ https://leetcode.com/problemset/all/?topicSlugs=java

✦ HackerRank ➽ https://www.hackerrank.com/domains/tutorials/10-days-of-java

✦ CodeGym ➽ https://codegym.cc/

✦ Codewars ➽ https://www.codewars.com/

✦ Project Euler ➽ https://projecteuler.net/archives

✦ Exercism ➽ https://exercism.org/tracks/java

✦ Coding Ninjas ➽ https://www.codingninjas.com/codestudio

✦ Practice-It! ➽ https://practiceit.cs.washington.edu/

✦ Codingame ➽ https://www.codingame.com/