Maps & Sets

put()

Associates key with specified value. If key already exists, replaces previous value with specified value.

// Map originally empty
exMap.put("Tom", 14); 
// Map now: Tom->14,  
exMap.put("John", 86); 
// Map now: Tom->14, John->86

putIfAbsent

Associates key with specified value if the key does not already exist or is mapped to null.

// Assume Map is: Tom->14, John->86
exMap.putIfAbsent("Tom", 20); 
// Key "Tom" already exists. Map is unchanged.
exMap.putIfAbsent("Mary", 13); 
// Map is now: Tom->14, John->86, Mary->13

get()

Returns the value associated with key. If key does not exist, return null.

// Assume Map is: Tom->14, John->86, Mary->13
exMap.get("Tom")  // returns 14 
exMap.get("Bob")  // returns null// Assume Map is: Tom->14, John->86, Mary->13

containsKey()

Returns true if key exists, otherwise returns false.

// Assume Map is: Tom->14, John->86, Mary->13
exMap.containsKey("Tom")  // returns true 
exMap.containsKey("Bob")  // returns false

containsValue()

Returns true if at least one key is associated with the specified value, otherwise returns false.

remove()

Removes the map entry for the specified key if the key exists.

// Assume Map is: Tom->14, John->86, Mary->13
exMap.containsValue(86)  // returns true (key "John" associated with value 86)
exMap.containsValue(17)  // returns false (no key associated with value 17)

clear()

Removes all map entries.

// Assume Map is: Tom->14, John->86, Mary->13
exMap.clear();  
// Map is now empty

doesn’t

HashMap ______ directly implement Iterable interface

entrySet()

for (Map.Entry<Integer,String> entry: hashMap.entrySet()){
	System.out.println("Key: entry.getKey() + Value + entry.getValue();
}

To iterate over a HashMap, you typically
use its ___________

iterable, generic

making a custom collection

make it _______ and ______

java.util

ArrayList, HashSet, and TreeSet are in package____________

add(), remove(), contains

ArrayList, HashSet, TreeSet have these 3 methods: _____, ______, _______

true

true or false: ArrayList, HashSet, TreeSet use enhanced for loops

compareTo()

TreeSet sorts the set according _________ order of the values

keys

TreeMap sorts the map according to the ______

interface

set is an ________

keySet()

Returns a Set containing all keys within the map.

// Assume Map is: Tom->14, John->86, Mary->13
keys = exMap.keySet();
// keys contains: "Tom", "John", "Mary"

values

Returns a Collection containing all values within the map.

// Assume Map is: Tom->14, John->86, Mary->13
values = exMap.values();
// values contains: 14, 86, 13

HashMap

map that provides faster access but doesn’t guarantee ordering

TreeMap

map that provides slightly slower access but maintains ordering of keys