Java Foundations: Data Types and Type Conversion

Java Foundations Data Types and Variables, Boolean, Integer, Char, String, Type Conversion

Your Course Instructors Svetlin Nakov George Georgiev

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Numeral Types, Text Types and Type Conversion Data Types and Variables

Table of Contents 1. Data Types and Variables 2. Integer and Real Number Types 3. Type Conversion 4. Boolean Type 5. Character and String Types 7

 Computers are machines that process data  Both program instructions and data are stored in the computer memory  Data is stored by using variables How Does Computing Work? 9 10110

 Variables have name, data type and value  Assignment is done by the operator "="  Example of variable definition and assignment  When processed, data is stored back into variables Variables 10 int count = 5; Data type Variable name Variable value

 A data type  Is a domain of values of similar characteristics  Defines the type of information stored in the computer memory (in a variable)  Examples:  Positive integers: 1, 2, 3, …  Alphabetical characters: a, b, c, …  Days of week: Monday, Tuesday, … What Is a Data Type? 11 Name Type Value age int 25 name String "Peter" size double 3.50 Computer memory

 A data type has:  Name (Java keyword)  Size (how much memory is used)  Default value  Example:  Name: int  Size: 32 bits (4 bytes)  Default value: 0 Data Type Characteristics 1 2 int: sequence of 32 bits in the memory int: 4 sequential bytes in the memory

 Always refer to the naming conventions of a programming language  camelCase is used in Java  Preferred form: [Noun] or [Adjective] + [Noun]  Should explain the purpose of the variable (Always ask "What does this variable contain?") Naming Variables 13 firstName, report, config, usersList, fontSize foo, bar, p, p1, populate, LastName, last_name

 Scope - where you can access a variable (global, local)  Lifetime - how long a variable stays in memory Variable Scope and Lifetime 1 4 String outer = "I'm inside the Main()"; for (int i = 0; i < 10; i++) { String inner = "I'm inside the loop"; } System.out.println(outer); // System.out.println(inner); Error Accessible in the main() Accessible only in the loop

 Variable span is how long before a variable is called  Always declare a variable as late as possible (e.g. shorter span) Variable Span 1 5 static void main(String[] args) { String outer = "I'm inside the main()"; for (int i = 0; i < 10; i++) String inner = "I'm inside the loop"; System.out.println(outer); // System.out.println(inner); Error } "outer" variable span

 Shorter span simplifies the code  Improves its readability and maintainability Keep Variable Span Short 1 6 for (int i = 0; i < 10; i++) { String inner = "I'm inside the loop"; } String outer = "I'm inside the main()"; System.out.println(outer); // System.out.println(inner); Error "outer" variable span – reduced

Integer Types in Java int, long, short, byte

18 Type Default Value Min Value Max Value Size byte 0 -128 (-27) 127 (27-1) 8 bit short 0 -32768 (-215) 32767 (215 - 1) 16 bit int 0 -2147483648 (-231) 2147483647 (231 – 1) 32 bit long 0 -9223372036854775808 (-263) 9223372036854775807 (263-1) 64 bit Integer Types in Java

 Depending on the unit of measure we can use different data types Centuries – Example 1 9 byte centuries = 20; short years = 2000; int days = 730484; long hours = 17531616; System.out.printf("%d centuries = %d years = %d days = %d hours.", centuries, years, days, hours) // 20 centuries = 2000 years = 730484 days = 17531616 hours.

 Integers have range (minimal and maximal value)  Integers could overflow  this leads to incorrect values Beware of Integer Overflow! 20 byte counter = 0; for (int i = 0; i < 130; i++) { counter++; System.out.println(counter); } 1 2 … 127 -128 -127

 Examples of integer literals:  The '0x' and '0X' prefixes mean a hexadecimal value  E.g. 0xFE, 0xA8F1, 0xFFFFFFFF  The 'l' and 'L' suffixes mean a long  E.g. 9876543L, 0L Integer Literals 2 1 int hexa = 0xFFFFFFFF; //-1 long number = 1L; //1

 Write a program that converts meters to kilometers formatted to the second decimal point  Examples: Problem: Convert Meters to Kilometres 22 1852 1.85 798 0.80 Scanner scanner = new Scanner(System.in); int meters = Integer.parseInt(scanner.nextLine()); double kilometers = meters / 1000.0; System.out.printf("%.2f", kilometers);

Real Number Types in Java float and double

 Floating-point types:  Represent real numbers, e.g. 1.25, -0.38  Have range and precision depending on the memory used  Sometimes behave abnormally in the calculations  May hold very small and very big values like 0.00000000000001 and 10000000000000000000000000000000000.0 What are Floating-Point Types? 24

 Floating-point types are:  float (±1.5 × 10−45 to ±3.4 × 1038)  32-bits, precision of 7 digits  double (±5.0 × 10−324 to ±1.7 × 10308)  64-bits, precision of 15-16 digits  The default value of floating-point types:  Is 0.0F for the float type  Is 0.0D for the double type Floating-Point Numbers 25

 Difference in precision when using float and double:  NOTE: The "f" suffix in the first statement!  Real numbers are by default interpreted as double  One should explicitly convert them to float PI Precision – Example 2 6 float floatPI = 3.141592653589793238f; double doublePI = 3.141592653589793238; System.out.println("Float PI is: " + floatPI); System.out.println("Double PI is: " + doublePI); 3. 1415927 3. 141592653589793

 Write a program that converts British pounds to US dollars formatted to 3rd decimal point  1 British Pound = 1.31 Dollars Problem: Pound to Dollars 27 80 104.800 double num = Double.parseDouble(scanner.nextLine()); double result = num * 1.31; System.out.printf("%.3f", result); 39 51.090

 Floating-point numbers can use the scientific notation, e.g.  1e+34, 1E34, 20e-3, 1e-12, -6.02e28 Scientific Notation 28 double d = 10000000000000000000000000000000000.0; System.out.println(d); // 1.0E34 double d2 = 20e-3; System.out.println(d2); // 0.02 double d3 = Double.MAX_VALUE; System.out.println(d3); //1.7976931348623157E308

 Integral division and floating-point division are different: Floating-Point Division 29 System.out.println(10 / 4); // 2 (integral division) System.out.println(10 / 4.0); // 2.5 (real division) System.out.println(10 / 0.0); // Infinity System.out.println(-10 / 0.0); // -Infinity System.out.println(0 / 0.0); // NaN (not a number) System.out.println(8 % 2.5); // 0.5 (3 * 2.5 + 0.5 = 8) System.out.println(10 / 0); // ArithmeticException

 Sometimes floating-point numbers work incorrectly!  Read more about IEEE 754 Floating-Point Calculations – Abnormalities 3 0 double a = 1.0f; double b = 0.33f; double sum = 1.33d; System.out.printf("a+b=%f sum=%f equal=%b", a+b, sum, (a + b == sum)); // a+b=1.33000001311302 sum=1.33 equal = false double num = 0; for (int i = 0; i < 10000; i++) num += 0.0001; System.out.println(num); // 0.9999999999999062

BigDecimal  Built-in Java Class  Provides arithmetic operations  Allows calculations with very high precision  Used for financial calculations 31 BigDecimal number = new BigDecimal(0); number = number.add(BigDecimal.valueOf(2.5)); number = number.subtract(BigDecimal.valueOf(1.5)); number = number.multiply(BigDecimal.valueOf(2)); number = number.divide(BigDecimal.valueOf(2));

 Write a program to enter n numbers and print their exact sum: Problem: Exact Sum of Real Numbers 32 2 1000000000000000000 5 1000000000000000005 2 0.00000000003 333333333333.3 333333333333.30000000003

Solution: Exact Sum of Real Numbers 33 int n = Integer.parseInt(sc.nextLine()); BigDecimal sum = new BigDecimal(0); for (int i = 0; i < n; i++) { BigDecimal number = new BigDecimal(sc.nextLine()); sum = sum.add(number); } System.out.println(sum);

Live Exercises Integer and Real Numbers

Type Conversion Implicit and Explicit Type Conversion

 Variables hold values of certain type  Type can be changed (converted) to another type  Implicit type conversion (lossless): variable of bigger type (e.g. double) takes smaller value (e.g. float)  Explicit type conversion (lossy) – when precision can be lost: Type Conversion 36 float heightInMeters = 1.74f; double maxHeight = heightInMeters; double size = 3.14; int intSize = (int) size; Explicit conversion Implicit conversion

 Write program to enter an integer number of centuries and convert it to years, days, hours and minutes Problem: Centuries to Minutes 37 The output is on one row 1 1 centuries = 100 years = 36524 days = 876576 hours = 52594560 minutes 5 centuries = 500 years = 182621 days = 4382904 hours = 262974240 minutes 5

Solution: Centuries to Minutes 38 int centuries = Integer.parseInt(sc.nextLine()); int years = centuries * 100; int days = (int) (years * 365.2422); int hours = 24 * days; int minutes = 60 * hours; System.out.printf( "%d centuries = %d years = %d days = %d hours = %d minutes", centuries, years, days, hours, minutes); (int) converts double to int The tropical year has 365.2422 days

Boolean Type True and False Values

 Boolean variables (boolean) hold true or false: Boolean Type 4 0 int a = 1; int b = 2; boolean greaterAB = (a > b); System.out.println(greaterAB); // False boolean equalA1 = (a == 1); System.out.println(equalA1); // True

 A number is special when its sum of digits is 5, 7 or 11  For all numbers 1…n print the number and if it is special Problem: Special Numbers 41 20 1 -> False 2 -> False 3 -> False 4 -> False 5 -> True 6 -> False 7 -> True 8 -> False 9 -> False 10 -> False 11 -> False 12 -> False 13 -> False 14 -> True 15 -> False 16 -> True 17 -> False 18 -> False 19 -> False 20 -> False

Solution: Special Numbers 42 int n = Integer.parseInt(sc.nextLine()); for (int num = 1; num <= n; num++) { int sumOfDigits = 0; int digits = num; while (digits > 0) { sumOfDigits += digits % 10; digits = digits / 10; } // TODO: check whether the sum is special }

Character Type Variables Holding a Letter or Special Char 'A'

 The character data type  Represents symbolic information  Is declared by the char keyword  Gives each symbol a corresponding integer code  Has a '0' default value  Takes 16 bits of memory (from U+0000 to U+FFFF)  Holds a single Unicode character (or part of character) The Character Data Type 4 4

 Each character has an unique Unicode value (int): Characters and Codes 4 5 char ch = 'a'; System.out.printf("The code of '%c' is: %d%n", ch, (int) ch); ch = 'b'; System.out.printf("The code of '%c' is: %d%n", ch, (int) ch); ch = 'A'; System.out.printf("The code of '%c' is: %d%n", ch, (int) ch); ch = 'щ'; // Cyrillic letter 'sht' System.out.printf("The code of '%c' is: %d%n", ch, (int) ch);

 Write a program that takes 3 lines of characters and prints them in reversed order with a space between them  Examples: Problem: Reversed Chars 46 A B C C B A 1 L & & L 1

Solution: Reversed Chars 47 Scanner scanner = new Scanner(System.in); char firstChar = scanner.nextLine().charAt(0); char secondChar = scanner.nextLine().charAt(0); char thirdChar = scanner.nextLine().charAt(0); System.out.printf("%c %c %c", thirdChar, secondChar, firstChar);

 Escaping sequences are:  Represent a special character like ', " or n (new line)  Represent system characters (like the [TAB] character t)  Commonly used escaping sequences are:  '  for single quote "  for double quote   for backslash n  for new line  uXXXX  for denoting any other Unicode symbol Escaping Characters 4 8

Character Literals – Example 4 9 char symbol = 'a'; // An ordinary character symbol = 'u006F'; // Unicode character code in a // hexadecimal format (letter 'o') symbol = 'u8449'; // 葉 (Leaf in Traditional Chinese) symbol = '‚'; // Assigning the single quote character symbol = ''; // Assigning the backslash character symbol = 'n'; // Assigning new line character symbol = 't'; // Assigning TAB character symbol = "a"; // Incorrect: use single quotes!

String Sequence of Letters "ABC"

The String Data Type  The string data type  Represents a sequence of characters  Is declared by the String keyword  Has a default value null (no value)  Strings are enclosed in quotes:  Strings can be concatenated  Using the + operator 51 String s = "Hello, Java";

 Strings are enclosed in quotes "":  Format strings insert variable values by pattern: Formatting Strings 52 String file = "C:Windowswin.ini"; The backslash is escaped by String firstName = "Svetlin"; String lastName = "Nakov"; String fullName = String.format( "%s %s", firstName, lastName);

 Combining the names of a person to obtain the full name:  We can concatenate strings and numbers by the + operator: Saying Hello – Examples 5 3 String firstName = "Ivan"; String lastName = "Ivanov"; String fullName = String.format( "%s %s", firstName, lastName); System.out.printf("Your full name is %s.", fullName); int age = 21; System.out.println("Hello, I am " + age + " years old");

 Read first and last name and delimiter  Print the first and last name joined by the delimiter Problem: Concat Names 54 John Smith -> John->Smith Linda Terry => Linda=>Terry Jan White <-> Jan<->White Lee Lewis --- Lee---Lewis

String firstName = sc.nextLine(); String lastName = sc.nextLine(); String delimiter = sc.nextLine(); String result = firstName + delimiter + lastName; System.out.println(result); Solution: Concat Names 55 Jan<->White

 …  …  … Summary 57  Variables – store data  Numeral types:  Represent numbers  Have specific ranges for every type  String and text types:  Represent text  Sequences of Unicode characters  Type conversion: implicit and explicit

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Java Foundations: Data Types and Type Conversion

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