Skip to content
Free public beta until December 4, 2026: every course is open, no card needed. After that, the first chapter of each course stays free and full access is a one-time $39 ($19 for up to 100 founding members chosen for helpful feedback). Your progress is kept. How the beta works

collection

An object that holds a group of other objects and grows or shrinks as they are added and removed.

Any java.util.Collection (a list, set or queue); maps belong to the framework but are not Collections.

Read the full section →