CS1150 Principles of Computer Science Final Review

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1 CS1150 Principles f Cmputer Science Final Review Yanyan Zhuang Department f Cmputer Science CS1150 UC. Clrad Springs

2 Numerical Data Types Name Range Strage Size byte 2 7 t (-128 t 127) 8-bit signed shrt 2 15 t ( t 32767) 16-bit signed int 2 31 t ( t ) 32-bit signed lng 2 63 t bit signed (i.e., t ) flat Negative range: 32-bit IEEE E+38 t -1.4E-45 Psitive range: 1.4E-45 t E+38 duble Negative range: 64-bit IEEE E+308 t -4.9E-324 Reading fr primitive data types: Psitive range: 4.9E-324 t E CS1150 UC. Clrad Springs

3 Integer Divisin +, -, *, /, and % 5 / 2 yields an integer / 2 yields a duble value % 2 yields 1 (the remainder f the divisin) ften called mdularperatin CS1150 UC. Clrad Springs

4 Java Identifiers An identifier A sequence f characters that cnsist f letters, digits, underscres (_), and dllar signs ($) N spaces Must start with a letter, an underscre (_), r a dllar sign ($) It cannt start with a digit An identifier cannt be A reserved wrd true, false, r null An identifier can be f any length CS1150 UC. Clrad Springs

5 Frmatting decimal utput Use DecimalFrmat class DecimalFrmat df = new DecimalFrmat("000.##"); System.ut.println(df.frmat(celsius)); 0: a digit #: a digit, zer shws as absent } 72.5 is shwn as } is shwn as Mre infrmatin alfrmat.html CS1150 UC. Clrad Springs

6 Frmatting decimal utput Use System.ut.frmat System.ut.frmat("the %s jumped ver the %s, %d times", "cw", "mn", 2); } the cw jumped ver the mn, 2 times System.ut.frmat("%.1f", ); } 10.3 // ne decimal pint System.ut.frmat("%.2f", ); } // tw decimal pints System.ut.frmat("%8.2f", ); } // Eight-wide, twdecimal pints CS1150 UC. Clrad Springs

7 Variables and Cnstants Variable Decimal numbers: t indicate flat/duble, use suffix f/d } Leaving ff the suffix, the number defaults t a duble flat flatvalue = 71.71f; } If leave ff f wuld get errr: cannt cnvert duble t flat duble dublevalue = d; } If yu left ff the d there is n issue Use duble (safe!) CS1150 UC. Clrad Springs

8 Variables and Cnstants Cnstant Used t stre a value that will NEVER change Cnstants fllw certain rules } Must have a name (a meaningful name, like variables) } Name cnstants with all uppercase letters (Java cnventin) } Declared using the keywrd final Example: final duble PI = ; Let s lk at cde samples CS1150 UC. Clrad Springs

9 Data Casting When yu explicitly tell Java t cnvert a variable frm ne data type t anther type Think f data types as cups f different sizes } Can put the cntents f a smaller variable (cup) int a larger variable (cup) } Cannt put the cntents frm a larger variable (cup) int a smaller variable (cup), withut lsing infrmatin } Cheat sheet: int (32 bits), duble (64 bits) CS1150 UC. Clrad Springs

10 Cnversin Rules When perfrming a binary peratin invlving tw perands f different types, Java autmatically cnverts the perand based n the fllwing rules: 1. If ne f the perands is duble, the ther is cnverted int duble. 2. Otherwise, if ne f the perands is flat, the ther is cnverted int flat. 3. Otherwise, if ne f the perands is lng, the ther is cnverted int lng. 4. Otherwise, bth perands are cnverted int int. 10

11 Augmented Assignment Operatrs +, -, *, / and % peratrs Each can be cmbined with the assignment peratr (=) a = a + 1; => a += 1; Same as -=, *=, /= and %= CS1150 UC. Clrad Springs

12 Increment and Decrement Operatrs Increment: ++ Decrement: -- Operatr can be placed befre r after variables (pstfix) int i = 1, j = 3; i++; // Same as i = i + 1; i will becme 2 j--; // Same as j = j 1; j will becme 2 Alternatively (prefix) int i = 1, j = 3; ++i; // Same as i = i + 1; i will becme 2 --j; // Same as j = j 1; j will becme 2 CS4500/5500 UC. Clrad Springs

13 Order f Operatrs (Sectin 3.15) Anything in parentheses expr++ expr-- (pstfix) expr --expr (unary plus/minus, prefix) (type) (Casting)! (nt) * / % (multiplicatin, divisin, remainder) + - (binary additin, subtractin) < <= > >= (relatinal peratrs) ==!= (equality) ^ (exclusive r) && (and) (r) = += -= *= /= %= (assignment, augmented assignment) CS1150 UC. Clrad Springs

14 If statement The else clause matches the mst recent if clause An else" always belngs with the mst recent if CS1150 UC. Clrad Springs

15 If statement T frce the else clause t match the first if clause, must add a pair f braces: int i = 1, j = 2, k = 3; if (i > j) { } if (i > k) else System.ut.println("A"); System.ut.println("B"); CS1150 UC. Clrad Springs

16 switch Statement Ntes switch expressin Must evaluate t a value f type char, byte, shrt, int } switch (x > 1) // Nt allwed - evaluates t a blean value } switch (x == 2) // Nt allwed - anther blean expressin CS4500/5500 UC. Clrad Springs

17 switch Statement Ntes Case values Are cnstants expressins Cannt cntain variables } case 0: system.ut.println("..."); // valid } case (x+1): system.ut.println("..."); // nt valid Thugh this is valid way t write the cases int value = 3; switch (value) { case 1:case 2:case 3: System.ut.println("case 1, 2, and 3"); break; case 4: System.ut.println("case 4"); break; default: System.ut.println("default"); } CS4500/5500 UC. Clrad Springs

18 switch Statement Ntes break statement int day = 3; switch (day) { case 1: case 2: case 3: case 4: case 5: System.ut.println("Weekday"); break; case 0: case 6: System.ut.println("Weekend"); } CS4500/5500 UC. Clrad Springs

19 Cnditinal Expressins Shrtcut way t write a tw-way if statement (if-else) Cnsists f the symbls? and : (aka the "ternary" peratr) result = expressin? value1 : value2 } expressin can be either a blean value r a statement that evaluates t a blean value } The cnditinal "expressin" is evaluated } If the expressin is true, value1 is returned } If the expressin is false, value2 is returned CS1150 UC. Clrad Springs

20 Rules fr While/D..while Lps The lp cnditin must be a blean expressin Blean expressin must be in parentheses Blean expressins are frmed using relatinal r lgical peratrs Lp cnditin Usually a statement befre the while lp "initializes" the lp cnditin t true Sme statement within the lp bdy eventually change the cnditin t false If the cnditin is never changed t false, the prgram is frever in the lp This is called an "infinite lp" Curly braces are nt necessary if nly ne statement in lp But best practice is t always include curly braces UC. Clrad Springs

21 Rules f fr lps The cntrl structure f the fr-lp needs t be in parentheses fr (i=0; i<= 2; i++) { statements; } The lp cnditin (i <= 2) must be a blean expressin The cntrl variable (i): nt recmmended t be changed within the fr-lp bdy Curly braces are nt necessary if nly ne statement in lp Best practice is t always include curly braces UC. Clrad Springs

22 Using break and cntinue Break in lps Used "break" in switch statements t end a case Can be used in a lp t terminate a lp Breaks ut f lp Cntinue in lps Used t end current iteratin f lp Prgram cntrl ges t end f lp bdy UC. Clrad Springs

23 Nte Yu may declare the cntrl variable utside/within the fr-lp fr (int j = 0; j <= 5; j++) { } } System.ut.println ("Fr lp iteratin = " + j); int j; fr (j = 0; j <= 5; j++) { System.ut.println ("Fr lp iteratin = " + j); Nte n variable scpe (the area a variable can be referenced) Declaring cntrl variable befre the fr lp cause its scpe t be inside and utside frlp Declaring the cntrl variable in the fr-lp causes its scpe t be nly inside the fr lp } If I tried t use the variable j utside the fr-lp - errr UC. Clrad Springs

24 Nte Mistakes t avid Infinite lps Off-by-ne errr Nested lps Knw hw t trace them UC. Clrad Springs

25 The Math Class Class cnstants: PI ( ) E ( base f natual lg) Class methds: Trignmetric Methds Expnent Methds Runding Methds min, max, abs, and randm Methds 25

26 Randm Numbers Math.randm() Hw t generate a randm integer between [lwer, upper)? } Example: int lwer=100, upper=120; } randmduble = Math.randm(); // [0.0, 1.0) } randmduble = randmduble * (upper-lwer); // [0.0, 20.0) } randmduble = lwer + randmduble; // [100.0, 120.0) } randmint = (int) randmduble; // cast duble à int Or in ne step } randmint = (int) (lwer + Math.randm() * (upper-lwer)); UC. Clrad Springs

27 Character Data Type Values: ne single character Use single qute t represent a character (dubles qutes are fr Strings) } char middleinitial = 'M'; } char numcharacter = '4'; // Assigns digit character 4 t numcharacter } System.ut.println(numCharacter); // Displays 4 Placing a character in it is n lnger a char: it is a String } char middleinitial = "M"; // Errr - cannt cnvert String t char CS1150 UC. Clrad Springs

28 ASCII Cde fr Cmmnly Used Characters Characters Cde Value in Decimal Unicde Value '0' t '9' 48 t 57 \u0030 t \u0039 'A' t 'Z' 65 t 90 \u0041 t \u005a 'a' t 'z' 97 t 122 \u0061 t \u007a Mre infrmatin: 28

29 Casting between char and Numeric Types int i = 'a'; // Same as int i = (int)'a'; System.ut.println ( i = " + i); // i = 97 all numeric peratrs can be applied t the char perands char c = 97; // Same as char c = (char)97; System.ut.println ("c = " + c); // c = a Increment and decrement can be used n char variables t get the next r preceding ASCII/Unicde character. char ch = 'a'; System.ut.println(++ch); //shws character b 29

30 Cmparing and Testing Characters if (ch >= 'A' && ch <= 'Z') System.ut.println(ch + " is an uppercase letter"); else if (ch >= 'a' && ch <= 'z') System.ut.println(ch + " is a lwercase letter"); else if (ch >= '0' && ch <= '9') System.ut.println(ch + " is a numeric character"); all numeric peratrs can be applied t the char perands 30

31 Hw t generate a randm character? A randm character between any tw characters ch1 and ch2 with ch1 < ch2 can be generated as: (char)(ch1 + Math.randm() * (ch2 ch1 + 1)) Example: randm upper case letter } (char)( A + Math.randm() * ( Z A + 1)) Example: randm numeric character } (char)( 0 + Math.randm() * ( )) UC. Clrad Springs

32 Hw t cnvert a numeric int character t its int value? Cnverting 0 t 0, etc. Example: hw t cnvert 0 t 0? 0-0 is is is 2... UC. Clrad Springs

33 The String Type A char is in single qutes and a String is in duble qutes char middleinitial = "M"; // Errr - can t cnvert String t char char middleinitial = 'M'; // Crrect string studentname = "Max" // Errr - uppercase "String" String studentname = 'Max'; // Errr - duble qutes String studentname = "Max"; // Crrect CS1150 UC. Clrad Springs

34 Strings and chars String methds (length, get char frm String) Read Strings/chars frm cnsle Cncatenate/cmpare Strings Cnverting between numbers and Strings Finding substrings Frmatting utput (%s, %d etc.) UC. Clrad Springs

35 Rules fr Methds A methd may r may nt return a value A methd must declare a return type! If a methd returns a value } Return type is the data type f the value being returned } The return statement is used t return the value If a methd des nt return a value } Return type in this case is vid } N return statement is needed (lk at max n return example) The values yu pass in must match the rder and type f the parameters declared in the methd UC. Clrad Springs

36 Overlading Methds -- Rules T be cnsidered an verladed methd Name - must be the same Return type - can be different - but yu cannt change nly the return type Frmal parameters - must be different Java will determine which methd t call based n the parameter list Smetimes there culd be several pssibilities Cmplier will pick the "best match" It is pssible that the methds are written in way that the cmplier cannt decide best match This is called ambiguus invcatin This results in an errr UC. Clrad Springs

37 Scpe f Lcal Variables A lcal variable: a variable defined inside a methd/blck Scpe: the part f the prgram where the variable can be referenced The scpe f a lcal variable starts frm its declaratin and cntinues t the end f the blck that cntains the variable A lcal variable must be declared befre it can be used. 37

38 Scpe f Lcal Variables, cnt. Can declare a lcal variable with the same name multiple times in different nnnesting blcks in a methd Cannt declare a lcal variable twice in nested blcks Frmal parameters are cnsidered lcal variables 38

39 Creating Arrays Cannt d anything with an array variable until after the array has been cnstructed with the new peratr: arrayrefvar = new datatype[arraysize]; Example: mylist = new duble[10]; //use new t give a size (2) assigns the reference f the array t the variable mylist mylist[0] references the first element in the array. mylist[9] references the last element in the array. (1) creates an array with 10 duble (i.e. it allcates memry) //allcate memry fr array 39

40 Accessing arrays Fr lps generally used with arrays since we knw hw many times the lp will ccur Example: assign the numbers 0 t 4 t numberlist // Assign the numbers 0 t 4 t numberlist array int[] numberlist = new int[5]; fr (int i = 0; i < 5; i++) { } numberlist[i] = i; System.ut.println("numberList[" + i + "] = " + numberlist[i]); Trying t access an element utside the range f an array it is an errr UC. Clrad Springs

41 Prcessing Arrays 1. (Initializing arrays with input values) 2. (Initializing arrays with randm values) 3. (Printing arrays) 4. (Summing all elements) 5. (Finding the largest element) 6. (Finding the smallest index f the largest element) 7. (Randm shuffling) 8. (Shifting elements) 41

42 Cpying Arrays Often, in a prgram, yu need t duplicate an array r a part f an array. In such cases yu culd attempt t use the assignment statement (=), as fllws: list2 = list1; 42

43 Cpying Arrays Using a lp: int[] surcearray = {2, 3, 1, 5, 10}; int[] targetarray = new int[surcearray.length]; fr (int i = 0; i < surcearrays.length; i++) targetarray[i] = surcearray[i]; 43

44 Passing Arrays t Methds public static vid printarray(int[] array) { fr (int i = 0; i < array.length; i++) { System.ut.print(array[i] + " "); } } Invke the methd int[] list = {3, 1, 2, 6, 4, 2}; printarray(list); Invke the methd printarray(new int[]{3, 1, 2, 6, 4, 2}); Annymus array 44

45 Pass By Value Java uses pass by value t pass arguments t a methd. There are imprtant differences between passing a value f variables f primitive data types and passing arrays. Fr a parameter f a primitive type value, the actual value is passed. Changing the value f the lcal parameter inside the methd des nt affect the value f the variable utside the methd. Fr a parameter f an array type, the value f the parameter cntains a reference t an array; this reference is passed t the methd. Any changes t the array that ccur inside the methd bdy will affect the riginal array that was passed as the argument. 45

46 Searching Arrays Searching is the prcess f lking fr a specific element in an array; fr example, discvering whether a certain scre is included in a list f scres. Searching is a cmmn task in cmputer prgramming. There are many algrithms and data structures devted t searching. In this sectin, tw cmmnly used appraches are discussed, linear search and binary search. public class LinearSearch { /** The methd fr finding a key in the list */ public static int linearsearch(int[] list, int key) { fr (int i = 0; i < list.length; i++) if (key == list[i]) [0] [1] [2] return i; list return -1; } key Cmpare key with list[i] fr i = 0, 1, } 46

47 Srting Arrays Srting, like searching, is als a cmmn task in cmputer prgramming. Many different algrithms have been develped fr srting. This sectin intrduces a simple, intuitive srting algrithms: selectin srt. 47

48 Object state and behavir An bject has tw imprtant pieces: state and behavir State The prperties (data fields) that define an bject: things an bject knws! A "dg" bject may have prperties such as clr, size, gender, etc. Behavir The methds that define an bject: things an bject des! A "dg" bject may have behavirs such as sleep, fetch, rllver, bark, sit, etc. UC. Clrad Springs

49 Classes Classes are cnstructs that define bjects f the same type. A Java class uses variables t define data fields and methds t define behavirs. Additinally, a class prvides a special type f methds, knwn as cnstructrs, which are invked t cnstruct bjects frm the class. 49

50 Cnstructrs, cnt. A cnstructr with n parameters is referred t as a n-arg cnstructr. Cnstructrs must have the same name as the class itself. Cnstructrs d nt have a return type nt even vid. Cnstructrs are invked using the new peratr when an bject is created. Cnstructrs play the rle f initializing bjects. 50

51 Cnstructrs cnt. A cnstructr can be verladed public StudentD (){ } public StudentD (String lastname, String firstname){ this.lastname = lastname; this.firstname = firstname; } public StudentD (int ID, int level){ this.studentid = ID; this.academiclevel = level; } UC. Clrad Springs

52 Accessing Object s Members qreferencing the bject s prperties (array s length): bjectrefvar.data e.g., mycircle.radius qinvking the bject s methd (String s length()): bjectrefvar.methdname(arguments) e.g., mycircle.getarea() 52

53 Static Variables, Cnstants, and Methds Static variables are shared by all the instances f the class. Static cnstants are final variables shared by all the instances f the class. Static methds are nt tied t a specific bject. T declare static variables, cnstants, and methds, use the static mdifier. 53

54 The this Keywrd qthe this keywrd is the name f a reference that refers t an bject itself. One cmmn use f the this keywrd is reference a class s hidden data fields. qanther cmmn use f the this keywrd t enable a cnstructr t invke anther cnstructr f the same class. 54

55 Calling Overladed Cnstructr public class Circle { private duble radius; public Circle(duble radius) { this.radius = radius; } public Circle() { this(1.0); } public duble getarea() { return this.radius * this.radius * Math.PI; } } Every instance variable be lngs t an instance represented by this, which is nrmally mitted th is m ust be explicitly used t refer ence th e d ata field radius f the bje ct being cnstructed th is is used t in vke an th er cnstr uct r 55

56 Scpe f Variables qthe scpe f instance and static variables is the entire class. They can be declared anywhere inside a class. qthe scpe f a lcal variable starts frm its declaratin and cntinues t the end f the blck that cntains the variable. A lcal variable must be initialized explicitly befre it can be used. 56

57 Visibility Mdifiers By default, a class, variable, r methd can be accessed by any class in the same package. q public The class, data, r methd is visible t any class in any package. q private The data r methds can be accessed nly by the declaring class. The getter and setter methds are used t read and mdify private prperties. 57

58 Inheritance When the definitin f a class is based n an existing class (called the superclass) The class that is inheriting (subclass) can use accessible date fields and methds frm superclass UC. Clrad Springs

59 Using the Keywrd super The keywrd super refers t the superclass f the class in which super appears. This keywrd can be used in tw ways: T call a superclass cnstructr: super() T call a superclass methd: super.methd() 59

60 Overriding vs. Overlading Overlading We discussed verlading in methds chapter Tw r mre methds with the same name but different frmal parameters The methds culd be in the same class r in different classes related by inheritance Overriding Occurs when dealing with inheritance A methd defined in the subclass that matches the signature and return type f the methd defined in superclass UC. Clrad Springs

61 Gd Luck!! UC. Clrad Springs

CS1150 Principles of Computer Science Midterm Review

CS1150 Principles of Computer Science Midterm Review CS1150 Principles f Cmputer Science Midterm Review Yanyan Zhuang Department f Cmputer Science http://www.cs.uccs.edu/~yzhuang CS1150 UC. Clrad Springs Office hurs 10/15, Mnday, 12:05 12:50pm 10/17, Wednesday