Basic Concepts Mehdi Einali Advanced Programming in Java 1

2 agenda Review User input Scanner Strong type checking Other flow-control structures switch break & continue Strings Arrays

3 review Variables Primitive data types Operators Methods Parameter passing Call by value Conditions If, else, else if Loops while do-while for

4 Variables Variables defined and initialized

5 Variables 2 types of variables Class variables(Fields) Local variables Method Variable Method parameter Block Variable There is no global variables Java use static binding for variables

6 Variables A variable always refers to its nearest enclosing binding.(Scoping)

7 User Input Print on console System.out.println How to read from console? Scanner Example: Scanner scanner = new Scanner(System.in); int n = scanner.nextInt(); double d = scanner.nextDouble();

8 Example Scanner scanner = new Scanner(System.in); int a = scanner.nextInt(); int b = scanner.nextInt(); long pow = power(a,b); System.out.println(pow);

9 Type Checking Java has a strong type-checking mechanism Some assignment is not permitted int intVal = 2; long longVal =12; intVal = longVal;  Syntax Error longVal = intVal;  OK intVal = (int)longVal;  OK (Type Casting)

10 Direct Type cast The arrows are transitive All other conversions need an explicit cast boolean is not convertible char is a special type

11 Type Conversion Grid

12 Type Conversion N : the conversion cannot be performed Y : the conversion is performed automatically and implicitly by Java C : the conversion is a narrowing conversion and requires an explicit cast Y* : the conversion is an automatic widening conversion, but that some of the least significant digits of the value may be lost by the conversion

13 Example i = ; //a big integer f = i; //f stores and approximation of i System.out.println(f);//output : E8 i = (int) f; System.out.println(i); //output : floating-point types are approximations of numbers They cannot always hold as many significant digits as the integer types

14 Comparison Compare doubles Using == with float or double is an anti- pattern An infinite loop: for (float f = 10f; f != 0; f -= 0.1) { System.out.println(f); }

15 Numeric Assignments Numeric Suffix Double d = d; Float f = 123f; Long l = l; byte b = 127;//Nothing Assignment Overflow Large long to int Lower bits are used No runtime error Large double to integer Brings a max int

16 Operators and cast Division (“/”) operates differently on integers and on doubles!

17 Flow controls

18 Structured programming Sequence Selection If-else switch-case Iteration for while do-while

19 Block Sometimes a group of statements needed to be executed in all or nothing manner It is same as single statement and can be replaced with a method

20 Block Variable

21 If-else Braces is optional for single statement Remember: place braces for clarify for indentation else will bind to last if

22 Short cut Boolean evaluation && vs &, || vs |

23 Loop-1 Constructs Initialize Step Termination condition

24 Loop-2 Watch out infinite loop

25 Switch statement switch (i) { case 1: System.out.println("1"); break; case 2: System.out.println("2"); break; default: System.out.println("default"); }

26 Break Jump out of loop block

27 Continue Stops the execution of the body of the loop and continues from the beginning of the loop

28 Nested loop outer: for (int i = 0; i < 10; i++){ inner: for (int j = 0; j < 10; j++) { if (j == 2){ break outer; } else { System.out.println(i); System.out.println(j); continue inner; }

29 Switch without break

30 Comments Comments are ignored by compiler One-line comment //nextInt = scanner.nextInt(); Multiple-line comment /*nextInt = scanner.nextInt(); for(int i=0;i<nextInt;i++){ System.out.println(i); } */ Javadoc comments /** *... text... */

31 String

32 String A sequence of characters Character: char ch = ‘a’; char ch = ‘1’; char ch = ‘#’; Strings: String st = “Ali”; String st = “123”; String st = “1”; String st = “”; String is not a primitive type

33 String String in C and C++ char* and char[] \0 at the end of String Some functions strlen, strcpy, … String in java is a class String in java is not equal to char[] Constant strings “salam!” “Hellow World!”

34 String and other types String input = "Nader and Simin, A Separation"; char ch = input.charAt(0); int i = input.indexOf("Nader"); int j = input.lastIndexOf("Simin"); String newS = input.replace("Separation", "Reconciliation"); String sth = newS + ch + i + j; System.out.println(sth);

35 String methods charAt concat  plus (+) operator contains startsWith endsWith indesxOf  first index of sth lastIndexOf replace substring length split

36 Immutable String String in java is an immutable class After creating a string, you can not change it If you want to change it, you should create a new string There is no such methods for strings: setCharAt(int) setValue(String) Methods like replace and replaceAll, do not change the value They return a new String

37 example What is the output of this code? String str = "Gholi"; str.replaceAll("li", "lam"); System.out.println(str); String str = "Gholi"; String replaced = str.replaceAll("li", "lam"); System.out.println(replaced);

38 Data Hierarchy Bit Byte Character Word

39 Java Characters Some characters are special characters Special characters are shown using backslash Examples: New line: \n Tab : \t Double-quote : \” Single-quote : \’ Backslash : \\

40 Arrays

41 Array Collections of related data items related data items of the same type Arrays are fixed-length entities they remain the same length once they are created An array is a group of variables called elements containing values that all have the same type The position number of the element is it’s index Array elements are sequentially located in memory

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43 samples Create an array of 10 integer elements int[] array = new int[10]; int array[] = new int[10];//equal Create an array of n characters char[] characters = new char[n]; Change value of 5’th element array[5] = 12; Retrieving value of n’th element char ch = array[n];

44 Array Creation Shortcut char[] array = new char[3]; array[0] = 'a'; array[1] = 's'; array[2] = 't'; The above code can be rewritten as: char[] array = {'a','s','t'}; Other examples: int[] numbers = {1,2,3,5,9,123}; boolean[] b = {true, true, false, true};

45 Multidimensional Arrays int[][] matrix = new int[3][4]; matrix[2][3] = 2; System.out.println(matrix[2][1]);

46 Unbalanced Multidimensional Array int[][] matrix = new int[3][]; matrix[0] = new int[2]; matrix[1] = new int [5]; matrix[2] = new int [4]; matrix[2][3] = 2; System.out.println(matrix[2][1]); matrix[0][3] = 2;//Runtime Error ArrayIndexOutOfBoundsException

47 Quiz (5 min ) e)exception

48 end