Strings. Piech, CS106A, Stanford University

Transcription

1 Strngs

2 Learnng Goals 1. Understand chars and Strngs 2. Wrte methods actng on Strngs

3 Text Applcatons

4 ow s text represented?

5 The varable type Strng Text s stored usng the varable type Strng. A Strng s a sequence of characters. publc vod run() { Strng text = hello! ; prntln(text);

6 e l l o!

7 e l l o!

8 e l l o! text.charat(ndex)

9 All characters n a strng have an ndex. You can access a character n the sequence va ts ndex

10 Strng Methods l l The strng.length() method returns the number of characters n the strng. Ths s one larger than the last vald ndex n the strng. the strng.charat() method returns the character at a gven ndex. m o m (length )

11 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frst = example.charat(0); prntln(frst); // prnts // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch);

12 Strng Methods publc vod run() { Strng example = " mom"; Console // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frst = example.charat(0); prntln(frst); // prnts // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch);

13 Strng Methods publc vod run() { Strng example = " mom"; Console // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frst = example.charat(0); prntln(frst); // prnts // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example m o m

14 Strng Methods publc vod run() { Strng example = " mom"; Console // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frst = example.charat(0); prntln(frst); // prnts // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example length m o m

15 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frst = example.charat(0); prntln(frst); // prnts Console // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example length m o m

16 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frst = example.charat(0); prntln(frst); // prnts Console // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example m o m length frst

17 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frst = example.charat(0); prntln(frst); // prnts Console // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example m o m length frst

18 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frst = example.charat(0); prntln(frst); // prnts Console // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example m o m length frst

19 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frstletter = example.charat(0); prntln(frstletter); // prnts Console // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example m o m length frst

20 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frstletter = example.charat(0); prntln(frstletter); // prnts Console // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example m o m length frst

21 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frstletter = example.charat(0); prntln(frstletter); // prnts Console // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example length frst m o m

22 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frstletter = example.charat(0); prntln(frstletter); // prnts Console // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example length frst ch m o m

23 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frstletter = example.charat(0); prntln(frstletter); // prnts Console // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example length frst m o m ch

24 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frstletter = example.charat(0); prntln(frstletter); // prnts Console // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example length frst m o m

25 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frstletter = example.charat(0); prntln(frstletter); // prnts Console // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example length frst m o m

26 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frstletter = example.charat(0); prntln(frstletter); // prnts Console // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example length frst m o m

27 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frstletter = example.charat(0); prntln(frstletter); // prnts Console // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example length frst m o m

28 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frstletter = example.charat(0); prntln(frstletter); // prnts Console // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example length frst m o m ch

29 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frstletter = example.charat(0); prntln(frstletter); // prnts Console // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example length frst m o m ch

30 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frstletter = example.charat(0); prntln(frstletter); // prnts Console // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example length frst m o m

31 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frstletter = example.charat(0); prntln(frstletter); // prnts Console // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example length frst m o m

32 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frstletter = example.charat(0); prntln(frstletter); // prnts Console // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example length frst m o m

33 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frstletter = example.charat(0); prntln(frstletter); // prnts Console // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example length frst m o m

34 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frstletter = example.charat(0); prntln(frstletter); // prnts Console // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example length frst m o m ch

35 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frstletter = example.charat(0); prntln(frstletter); // prnts Console // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example length frst m o m ch

36 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frstletter = example.charat(0); prntln(frstletter); // prnts Console // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example length frst m o m ch

37 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frstletter = example.charat(0); prntln(frstletter); // prnts // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example m o m length frst m o m 5 Console ch m

38 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frstletter = example.charat(0); prntln(frstletter); // prnts // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example m o m length frst m o m 5 Console

39 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frstletter = example.charat(0); prntln(frstletter); // prnts // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example m o m length frst m o m Console

40 Strng Methods publc vod run() { Strng example = " mom"; // example of length method nt length = example.length(); prntln(length); // prnts // example of getcharat char frstletter = example.charat(0); prntln(frstletter); // prnts // loop that prnts letters one-by-one for(nt = 0; < example.length(); ++) { char ch = example.charat(); prntln(ch); example m o m length frst m o m Console

41 ow are characters represented?

42 The varable type char l l The prmtve type char represents a sngle character or glyph. Some examples: char lettera = 'A'; char plus = '+' char zero = '0'; char space = ' '; char newlne = '\n'; // specal char frst = text.charat(0);

43 ASCII * Ths s only the frst half of the table The letter A, for example, has the ASCII value 5 Usng portons of sldes by Erc Roberts

44 A -> Z are sequental. a -> z are sequental. 0 -> 9 are sequental.

45 Useful Character methods publc vod run() { Strng str = readlne("lne: "); char ch = str.charat(0); prntln("orgnal frst char: " + ch); ch = Character.toUpperCase(ch); prntln("uppercase frst char: " + ch); f(character.sletter(ch)) { prntln("it s a letter!");

46 Character Methods

47 Useful Character methods statc boolean sdgt(char ch) Determnes f the specfed character s a dgt. statc boolean sletter(char ch) Determnes f the specfed character s a letter. statc boolean sletterordgt(char ch) Determnes f the specfed character s a letter or a dgt. statc boolean slowercase(char ch) Determnes f the specfed character s a lowercase letter. statc boolean suppercase(char ch) Determnes f the specfed character s an uppercase letter. statc boolean swhtespace(char ch) Determnes f the specfed character s whtespace (spaces and tabs). statc char tolowercase(char ch) Converts ch to ts lowercase equvalent, f any. If not, ch s returned unchanged. statc char touppercase(char ch) Converts ch to ts uppercase equvalent, f any. If not, ch s returned unchanged. Usng portons of sldes by Erc Roberts

48 Strngs have some unque propertes

49 Strngs are Immutable l Java strngs are mmutable: once a strng has been created you cannot set characters. l To change a strng: l l Create a new strng holdng the new value you want t to have va concatenaton. Reassgnng the Strng varable (that s allowed). l Important consequence: f you pass a Strng nto a method, that method cannot modfy that strng.

50 Strngs are often made through concatenaton publc vod run() { Strng s1 = Breakout"; Strng s2 = t was awesome"; Strng s3 = "I crushed " + s1 + " and " + s2; prntln(s3); I crushed Breakout and t was awesome

51 Many strng algorthms use the loop and construct pattern.

52 Reversng a Strng e l l o!

53 Reversng a Strng e l l o!

54 Reversng a Strng e l l o! e

55 Reversng a Strng e l l o! l e

56 Reversng a Strng e l l o! l l e

57 Reversng a Strng e l l o! o l l e

58 Reversng a Strng e l l o!! o l l e

59 reversestrng publc vod run() { prntln("ths program reverses a strng."); prvate Strng Strng str = readlne("enter reversestrng(strng a strng: str) "); { Strng Strng rev result = reversestrng(str); = ""; prntln(str for ( + = " 0; spelled < str.length(); backwards s ++ " + ) rev); { result = str.charat() + result; rev return result; DESSERTS str STRESSED result DESSERTS SERTS STS str STRESSED ReverseStrng Ths program reverses a strng. Enter a strng: STRESSED STRESSED spelled backwards s DESSERTS Usng portons of sldes by Erc Roberts skp smulaton

60 Useful Strng methods nt length() Returns the length of the strng char charat(nt ndex) Returns the character at the specfed ndex. Note: Strngs ndexed startng at 0. Strng substrng(nt p1, nt p2) Returns the substrng begnnng at p1 and extendng up to but not ncludng p2 Strng substrng(nt p1) Returns substrng begnnng at p1 and extendng through end of strng. boolean equals(strng s2) Returns true f strng s2 s equal to the recever strng. Ths s case senstve. nt compareto(strng s2) Returns nteger whose sgn ndcates how strngs compare n lexcographc order nt ndexof(char ch) or nt ndexof(strng s) Returns ndex of frst occurrence of the character or the strng, or -1 f not found Strng tolowercase() or Strng touppercase() Returns a lowercase or uppercase verson of the recever strng Usng portons of sldes by Erc Roberts

61 Palndrome l l A palndrome s a strng that reads the same forwards and backwards. For example: l l l l l l Abba Racecar Kayak Mr. Owl ate my metal worm. Go hang a salam! I'm a lasagna hog. Elu par cette crapule

62 Let s Code t!

63 prvate boolean spalndrome(strng orgnal) { Strng reversed = reverse(orgnal); return reversed == orgnal;

64 Use.equals to compare strngs, not ==

65 prvate boolean spalndrome(strng orgnal) { Strng reversed = reverse(orgnal); return reversed.equals(orgnal);

66 Some test cases l Let's test our program on some examples: l l l l Racecar Kayak Mr. Owl ate my metal worm. Go hang a salam! I'm a lasagna hog. l Wll t work?

67 More Palndromes ere are some palndromes n other languages: l بلح تعلق تحت قلعة حلب (Dates hang underneath a castle n alab) l 여보, 안경안보여 (oney, I can't see my glasses) l कड़क (a loud thunderous sound) l 上海自來水來自海上 (Shangha tap water orgnates from "above" the ocean) The comedan Dmtr Martn also has a routne about palndromes; check t out at

68 Stress Test A man, a plan, a caret, a ban, a myrad, a sum, a lac, a lar, a hoop, a pnt, a catalpa, a gas, an ol, a brd, a yell, a vat, a caw, a pax, a wag, a tax, a nay, a ram, a cap, a yam, a gay, a tsar, a wall, a car, a luger, a ward, a bn, a woman, a vassal, a wolf, a tuna, a nt, a pall, a fret, a watt, a bay, a daub, a tan, a cab, a datum, a gall, a hat, a tag, a zap, a say, a jaw, a lay, a wet, a gallop, a tug, a trot, a trap, a tram, a torr, a caper, a top, a tonk, a toll, a ball, a far, a sax, a mnm, a tenor, a bass, a passer, a captal, a rut, an amen, a ted, a cabal, a tang, a sun, an ass, a maw, a sag, a jam, a dam, a sub, a salt, an axon, a sal, an ad, a wad, a radan, a room, a rood, a rp, a tad, a parah, a revel, a reel, a reed, a pool, a plug, a pn, a peek, a parabola, a dog, a pat, a cud, a nu, a fan, a pal, a rum, a nod, an eta, a lag, an eel, a batk, a mug, a mot, a nap, a maxm, a mood, a leek, a grub, a gob, a gel, a drab, a ctadel, a total, a cedar, a tap, a gag, a rat, a manor, a bar, a gal, a cola, a pap, a yaw, a tab, a raj, a gab, a nag, a pagan, a bag, a jar, a bat, a way, a papa, a local, a gar, a baron, a mat, a rag, a gap, a tar, a decal, a tot, a led, a tc, a bard, a leg, a bog, a burg, a keel, a doom, a mx, a map, an atom, a gum, a kt, a baleen, a gala, a ten, a don, a mural, a pan, a faun, a ducat, a pagoda, a lob, a rap, a keep, a np, a gulp, a loop, a deer, a leer, a lever, a har, a pad, a tapr, a door, a moor, an ad, a rad, a wad, an alas, an ox, an atlas, a bus, a madam, a jag, a saw, a mass, an anus, a gnat, a lab, a cadet, an em, a natural, a tp, a caress, a pass, a baronet, a mnmax, a sar, a fall, a ballot, a knot, a pot, a rep, a carrot, a mart, a part, a tort, a gut, a poll, a gateway, a law, a jay, a sap, a zag, a tat, a hall, a gamut, a dab, a can, a tabu, a day, a batt, a waterfall, a patna, a nut, a flow, a lass, a van, a mow, a nb, a draw, a regular, a call, a war, a stay, a gam, a yap, a cam, a ray, an ax, a tag, a wax, a paw, a cat, a valley, a drb, a lon, a saga, a plat, a catnp, a pooh, a ral, a calamus, a daryman, a bater, a canal Panama!