Maps

• Maps

  • dynamic data structure that stores key/value pairs
  • import java.util.Map
• Hash map


  keys are unordered
• Linked Hash map


  keys are ordered based on sequence elements were added
• tree map


  keys are sorted
• put key/value pair

  • adds a key-value pair to the map if the key is not already in the map and returns null
  • replaces the value associated with the key and returns the previous value associated with key
• remove key/value pair

  • removes a key-value pair from the map if the key is in the map and returns the previous value associated with key
  • returns null if the key was not in the map
• get value

  • returns the value associated with key if the key is in the map
  • returns null if the key was not in the map
• size


  returns the number of key-value pairs in the map
• for each

  • display all of the key-value pairs in the map
  • studentSortedMap.forEach( (key, value) ->{System.out.println(key + “: " + value);});