https://docs.oracle.com/javase/8/docs/api/java/util/Map.html

Test.java

import java.util.Map;
import java.util.HashMap;
class Java {
  public static void main(String[] args) {
    // Associate(or map) string values to numbers(Integerrs)
    Map<String, Integer> map = new HashMap<String, Integer>();
    // map["joe"] = 1;
    map.put("Joe", 1);
    map.put("Nate", 2);
    // joe = 1, nate = 2
    int joe = map.get("Joe");
    int nate = map.get("Nate");
    
    // Say we have a bunch of integers from 1 to 10^31 -1(the max value of integers in java)
    // If we create an array of that size, we'll be using a minimum of 68 GB of RAM.
    // If we only have two values that need to be associated(0 and 10^31 -1), it would be
    // impossible to do with an array.  However, we can do with with a map, and while the memory
    // usage isn't as direcly predictable(maps are complicated to write), it will probably use less than
    // 100 bytes
    
    // When dealing with generics you can use <> to avoid repeating yourself(Java 7+)
    Map<Integer, String> map2 = new HashMap<>();
    
    map2.put(1, "Joe");
    map2.put(2, "Nate");
  }
    
    
}