Not All Data is Linear

Transcription

1 HashMap

2 Not All Data is Linear

3 HashMap<String, String> animals = new HashMap<String, String>(); animals.put("dog", "bark"); animals.put("cat", "meow"); animals.put("nubian ibex", "(silence)"); animals.get("dog"); // Returns "bark" animals.put("dog", "woof"); println(animals.get("fox")); animals.containskey("cat"); // Returns null // Returns true

4 HashMap<String, String> animals = new HashMap<String, String>(); animals.put("dog", "bark"); animals.put("cat", "meow"); animals.put("nubian ibex", "(silence)"); animals.get("dog"); // Returns "bark" animals.put("dog", "woof"); println(animals.get("fox")); animals.containskey("cat"); // Returns null // Returns true

5 HashMap<String, String> animals = new HashMap<String, String>(); animals.put("dog", "bark"); animals.put("cat", "meow"); animals.put("nubian ibex", "(silence)"); animals.get("dog"); // Returns "bark" animals.put("dog", "woof"); println(animals.get("fox")); animals.containskey("cat"); // Returns null // Returns true

6 dog bark HashMap<String, String> animals = new HashMap<String, String>(); animals.put("dog", "bark"); animals.put("cat", "meow"); animals.put("nubian ibex", "(silence)"); animals.get("dog"); // Returns "bark" animals.put("dog", "woof"); println(animals.get("fox")); animals.containskey("cat"); // Returns null // Returns true

7 dog bark HashMap<String, String> animals = new HashMap<String, String>(); animals.put("dog", "bark"); animals.put("cat", "meow"); animals.put("nubian ibex", "(silence)"); To animals.get("dog"); To add // add a Returns a key/value key/value pair "bark" pair to to a a HashMap, HashMap, use use the the syntax syntax animals.put("dog", "woof"); println(animals.get("fox")); // map.put(key, Returns null animals.containskey("cat"); // value) Returns true

8 dog bark HashMap<String, String> animals = new HashMap<String, String>(); animals.put("dog", "bark"); animals.put("cat", "meow"); animals.put("nubian ibex", "(silence)"); animals.get("dog"); // Returns "bark" animals.put("dog", "woof"); println(animals.get("fox")); animals.containskey("cat"); // Returns null // Returns true

9 dog bark cat meow HashMap<String, String> animals = new HashMap<String, String>(); animals.put("dog", "bark"); animals.put("cat", "meow"); animals.put("nubian ibex", "(silence)"); animals.get("dog"); // Returns "bark" animals.put("dog", "woof"); println(animals.get("fox")); animals.containskey("cat"); // Returns null // Returns true

10 dog bark cat meow HashMap<String, String> animals = new HashMap<String, String>(); animals.put("dog", "bark"); animals.put("cat", "meow"); animals.put("nubian ibex", "(silence)"); animals.get("dog"); // Returns "bark" animals.put("dog", "woof"); println(animals.get("fox")); animals.containskey("cat"); // Returns null // Returns true

11 dog bark cat meow nubian ibex (silence) HashMap<String, String> animals = new HashMap<String, String>(); animals.put("dog", "bark"); animals.put("cat", "meow"); animals.put("nubian ibex", "(silence)"); animals.get("dog"); // Returns "bark" animals.put("dog", "woof"); println(animals.get("fox")); animals.containskey("cat"); // Returns null // Returns true

12 dog bark cat meow nubian ibex (silence) HashMap<String, String> animals = new HashMap<String, String>(); animals.put("dog", "bark"); animals.put("cat", "meow"); animals.put("nubian ibex", "(silence)"); animals.get("dog"); // Returns "bark" animals.put("dog", "woof"); println(animals.get("fox")); animals.containskey("cat"); // Returns null // Returns true

13 dog bark cat meow nubian ibex (silence) HashMap<String, String> animals = new HashMap<String, String>(); animals.put("dog", "bark"); animals.put("cat", "meow"); animals.put("nubian ibex", "(silence)"); To To look look up up the the value value animals.get("dog"); // Returns "bark" associated with with a key: key: animals.put("dog", "woof"); println(animals.get("fox")); // Returns null animals.containskey("cat"); // Returns map.get(key) true

14 dog bark cat meow nubian ibex (silence) HashMap<String, String> animals = new HashMap<String, String>(); animals.put("dog", "bark"); animals.put("cat", "meow"); animals.put("nubian ibex", "(silence)"); animals.get("dog"); // Returns "bark" animals.put("dog", "woof"); println(animals.get("fox")); animals.containskey("cat"); // Returns null // Returns true

15 dog bark cat meow nubian ibex (silence) HashMap<String, String> animals = new HashMap<String, String>(); animals.put("dog", "bark"); animals.put("cat", "meow"); animals.put("nubian ibex", "(silence)"); animals.get("dog"); // Returns "bark" animals.put("dog", "woof"); println(animals.get("fox")); animals.containskey("cat"); // Returns null // Returns true

16 dog woof cat meow nubian ibex (silence) HashMap<String, String> animals = new HashMap<String, String>(); animals.put("dog", "bark"); animals.put("cat", "meow"); animals.put("nubian ibex", "(silence)"); animals.get("dog"); // Returns "bark" animals.put("dog", "woof"); println(animals.get("fox")); animals.containskey("cat"); // Returns null // Returns true

17 dog woof cat meow nubian ibex (silence) HashMap<String, String> animals = new HashMap<String, String>(); animals.put("dog", "bark"); animals.put("cat", "meow"); If If you you put a animals.put("nubian ibex", "(silence)"); animals.get("dog"); // Returns key/value "bark" pair pair where where animals.put("dog", "woof"); the the key key exists, the the old old println(animals.get("fox")); // Returns value null animals.containskey("cat"); // Returns value is true is replaced.

18 dog woof cat meow nubian ibex (silence) HashMap<String, String> animals = new HashMap<String, String>(); animals.put("dog", "bark"); animals.put("cat", "meow"); animals.put("nubian ibex", "(silence)"); animals.get("dog"); // Returns "bark" animals.put("dog", "woof"); animals.get("fox"); // Returns null animals.containskey("cat"); // Returns true

19 dog woof cat meow nubian ibex (silence) HashMap<String, String> animals = new HashMap<String, String>(); animals.put("dog", "bark"); animals.put("cat", "meow"); animals.put("nubian ibex", "(silence)"); If If you you get a key key that that animals.get("dog"); // Returns "bark" isn't isn't in in a map, map, the the animals.put("dog", "woof"); animals.get("fox"); // Returns method null returns null. animals.containskey("cat"); // Returns true

20 dog woof cat meow nubian ibex (silence) HashMap<String, String> animals = new HashMap<String, String>(); animals.put("dog", "bark"); animals.put("cat", "meow"); animals.put("nubian ibex", "(silence)"); animals.get("dog"); // Returns "bark" animals.put("dog", "woof"); animals.get("fox"); animals.containskey("cat"); // Returns null // Returns true

21 dog woof cat meow nubian ibex (silence) HashMap<String, String> animals = new HashMap<String, String>(); animals.put("dog", "bark"); animals.put("cat", "meow"); animals.put("nubian ibex", "(silence)"); animals.get("dog"); // Returns "bark" animals.put("dog", "woof"); animals.get("fox"); // Returns null animals.containskey("cat"); // Returns true

22 dog woof cat meow nubian ibex (silence) HashMap<String, String> animals = new HashMap<String, String>(); animals.put("dog", "bark"); animals.put("cat", "meow"); You animals.put("nubian ibex", "(silence)"); You can can check check whether whether a a animals.get("dog"); // Returns key key exists exists "bark" in in the the map: map: animals.put("dog", "woof"); map.containskey(key) animals.get("fox"); // Returns null animals.containskey("cat"); // Returns true

23 dog woof cat meow nubian ibex (silence) HashMap<String, String> animals = new HashMap<String, String>(); animals.put("dog", "bark"); animals.put("cat", "meow"); animals.put("nubian ibex", "(silence)"); animals.get("dog"); // Returns "bark" animals.put("dog", "woof"); animals.get("fox"); // Returns null animals.containskey("cat"); // Returns true

24 Basic HashMap Operations HashMap has two type arguments: HashMap<KeyType, ValueType> To insert a key/value pair: map.put(key, value) To look up the value associated with a key: map.get(key) To check whether a key exists: map.containskey(key)

25 Making HashMap Shine

26 Exploring the US

27 Time-Out for Announcements!

28 Friday Four Square! Today at 4:15PM at Gates CS

29 Midterms Graded Midterms graded, available for pickup in a filing cabinet in the Gates B Wing. Right inside the entrance marked Stanford Engineering Venture Fund Laboratories. If you'd like to submit your exam for a regrade, attach a coversheet letting us know what to look at and hand your exam to Vikas or Keith. Deadline: next Wednesday at 3:15PM.

30 Assignment 5 Assignment 5 (Array Algorithms) is due one week from today. Recommendation: Complete Steganography by Monday and start working on Tone Matrix.

31 Back to CS106A!

32 Making Music

33 The Keyboard File Format note-file-name x y width height is white key?

34 The xkcd Color Survey

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38 The xkcd Color Survey Volunteers (online) were shown a randomly-chosen color and asked to name the color. The result is (after filtering) about 2.8 million RGB triplets and their names. What do people think the colors are?

39 The Color File Format color-name red green blue

40 Displaying Colors The HSB Color Format Choose the hue (what color), saturation (how intense), and brightness (absolute brightness). Each choice in the range from 0.0 to 1.0.

41 How to Structure the Data? blue red gray associate each color name with a list of RGB triplets

42 How to Structure the Data? blue red gray HashMap<color name, list of RGB triplets>

43 How to Structure the Data? blue red gray HashMap<String, list of RGB triplets>

44 How to Structure the Data? blue red gray HashMap<String, ArrayList<RGB triplet>>

45 How to Structure the Data? blue red gray BHashMap<String, ArrayList<int[]>>B

46 For More Information