Introduction to Collections

A collection object can store an arbitrary number of other objects. There is no pre-defined limit to number of objects.

• Typically we use ArrayList in Java. To save time, we can use ‘diamond notation’, as ArrayList<>(); to avoid typing out the type again. Type is inferred from the variable we are assigning to.

A class library is a library of useful classes. These libraries are referred to as *packages* when working with Java.

A loop can be used to execute a block of statements repeatedly without having to write them multiple times.

• We can use a for-each loop to loop through a collection such as an ArrayList.

  for (String item : items) {
    // do something with item
  }

An iterator is an object that provides functionality to iterate over all elements of a collection.