http://blog.tomtasche.at/2016/05/java-101-collections.html

ListExample.java

List<String> data = new LinkedList<String>();
// or if you know the amount of data upfront:
List<String> data = new ArrayList<String>(3);
data.add("hello");
data.add("hello");
data.add("bye");

System.out.println(data.size()); // 3

// in order to lookup data you always have to iterate the whole list until you find the value you're looking for
for (String dataString : data) {
  if (dataString.equals("bye")) {
    System.out.println("data found");
  }
}

MapExample.java

Map<String, String> data = new HashMap<String, String>();
data.put("greeting", "hello");
data.put("greeting", "hello");
data.put("farewell", "bye");

System.out.println(data.size()); // 2

// you can look up data efficently using contains
if (data.contains("farewell")) { // or: data.get("farewell").equals("bye")
  System.out.println("data found");
}

SetExample.java

Set<String> data = new HashSet<String>();
data.put("hello");
data.put("hello");
data.put("bye");

System.out.println(data.size()); // 2

// you can look up data efficently using contains
if (data.contains("bye")) {
  System.out.println("data found");
}