Chapter 2: Java Fundamentals Type conversion,String

Chapter Objectives Type Conversion String Class Commonly Used String Methods Parsing Numeric Strings Commonly Used Escape Sequences

Variables – Cont. Float The default type of floating point numbers is double. The declaration : float rate = 15.5f ; without the f, the compiler will generate an error 3

Variables – Cont. Char When using the char data type, you enclose each character represented within single quotations marks. Ex: char c = ‘A’ char x = ‘&’ char space = ‘ ‘ Each character is represented by a value (‘A’ is represented by the value 65) 4

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Type Conversion (Casting) Used: to change one data type to another. to avoid implicit type coercion. Syntax: (dataTypeName) expression Expression evaluated first, then the value is converted to dataTypeName Java Programming: From Problem Analysis to Program Design, Second Edition 6

Type Conversion (Casting) Examples: 1. (int)( ) = (int)(7.9) + (int)(6.7) = (double)(17) = (double)(8+3) = (double)11 = (double)(7) /2 = 7.0/2 = (double)(7/2) = (int)(7.8+(double)(15)/2) = (int)15.3 =15 Java Programming: From Problem Analysis to Program Design, Second Edition 7

Type Conversion (Casting) 8. (int)(‘A’) = (int)(‘8’) = (char)(65) = ‘A’ 11. (char) (56) = ‘8’ Java Programming: From Problem Analysis to Program Design, Second Edition 8

The class String Contains operations to manipulate strings. String: Sequence of zero or more characters. Enclosed in double quotation marks. Is processed as a single unit. Null or empty strings have no characters. “ “ Every character has a relative position, the first character is in position 0. Java Programming: From Problem Analysis to Program Design, Second Edition 9

10 The class String Java system automatically makes the class String available (i.e no need to import this class ) Example : Consider the following declaration : String sentence ; sentence = “programming with java”

The class String Length of the string is the number of characters in it. When determining the length of a string, blanks count. Example : “ “  has length = 0 “abc”  has length = 3, position of a = 0,b= 1, c= 2 “a boy”  has length = 5 Java Programming: From Problem Analysis to Program Design, Second Edition 11

Java Programming: From Problem Analysis to Program Design, Second Edition12 Some Commonly Used String Methods

Java Programming: From Problem Analysis to Program Design, Second Edition13 Some Commonly Used String Methods

Java Programming: From Problem Analysis to Program Design, Second Edition14 Some Commonly Used String Methods

Java Programming: From Problem Analysis to Program Design, Second Edition15 Some Commonly Used String Methods

Java Programming: From Problem Analysis to Program Design, Second Edition16 Examples on string methods String s1, s2, s3 ; s1 = “abcdefeg” ; System.out.println( s1.length() ); // 8 System.out.println(s1.charAt(3)); //d System.out.println(s1.indexOf(‘e’)); //4 System.out.println(s1.indexOf(“cd”)); //2 System.out.println(s1.toUpperCase()); //ABCDEFEG

Java Programming: From Problem Analysis to Program Design, Second Edition17 Examples on string methods System.out.println(s1.substring(1, 4)); //bcd System.out.println(s1 + “xyz”); // abcdefegxyz System.out.println( s1.replace(‘d’,’D’)); // abcDefeg System.out.println(s1.charAt(4) ); // e System.out.println(s1.indexOf(‘b’)); // 1 System.out.println(s1.indexOf(‘e’,5)); // 6

Java Programming: From Problem Analysis to Program Design, Second Edition 18 Input Reading a Single Character if ch is a char variable. To input A into ch, you can use the following statement: ch = console.next().charAt(0);

Java Programming: From Problem Analysis to Program Design, Second Edition19 Parsing Numeric Strings  Integer, Float, and Double are classes designed to convert a numeric string into a number.  These classes are called wrapper classes.  parseInt is a method of the class Integer, which converts a numeric integer string into a value of the type int.  parseFloat is a method of the class Float and is used to convert a numeric decimal string into an equivalent value of the type float.  parseDouble is a method of the class Double, which is used to convert a numeric decimal string into an equivalent value of the type double.

Java Programming: From Problem Analysis to Program Design, Second Edition20 Parsing Numeric Strings  A string consisting of only integers or decimal numbers is called a numeric string.  To convert a string consisting of an integer to a value of the type int, we use the following expression: Integer.parseInt(strExpression) Example: Integer.parseInt("6723") = 6723 Integer.parseInt("-823") = -823

Java Programming: From Problem Analysis to Program Design, Second Edition21 Parsing Numeric Strings  To convert a string consisting of a decimal number to a value of the type float, we use the following expression: Float.parseFloat(strExpression) Example: Float.parseFloat("34.56") = Float.parseFloat(" ") =  To convert a string consisting of a decimal number to a value of the type double, we use the following expression: Double.parseDouble(strExpression) Example: Double.parseDouble("345.78") = Double.parseDouble(" ") =

Java Programming: From Problem Analysis to Program Design, Second Edition22 Formatting Output with printf The syntax to use the method printf to produce output on the standard output device is: System.out.printf(formatString); or System.out.printf(formatString,argumentList) ; formatString is a string specifying the format of the output and argumentList is a list of arguments. argumentList is a list of arguments that consists of constant values, variables, or expressions. If there is more than one argument in argumentList, the arguments are separated with commas.

Java Programming: From Problem Analysis to Program Design, Second Edition23 Formatting Output with printf System.out.printf("Hello there!"); Consists of only the format string and the statement: System.out.printf("There are %.2f inches in %d centimeters.%n", centimeters / 2.54, centimeters); Consists of both the format string and argumentList. %.2f and %d are called format specifiers. By default, there is a one-to-one correspondence between format specifiers and the arguments in argumentList. The first format specifier, %.2f, is matched with the first argument, which is the expression centimeters / 2.54.

Java Programming: From Problem Analysis to Program Design, Second Edition24 Formatting Output with printf The second format specifier, %d, is matched with the second argument, which is centimeters. The format specifier %n positions the insertion point at the beginning of the next line. If centimeters = 150  150/2.54 = The o/p would be : There are inches in 150 centimeters The output of a printf statement is right-justified by default. To force the output to be left-justified, negative column widths may be used.

Java Programming: From Problem Analysis to Program Design, Second Edition25 Example1 public class Example3_6 { public static void main (String[] args) { int num = 763; double x = ; String str = "Java Program."; System.out.println(" "); System.out.printf ( "%5d%7.2f%15s%n", num, x, str); System.out.printf ("%15s%6d%9.2f %n", str, num, x); }

Java Programming: From Problem Analysis to Program Design, Second Edition26 Example1 Sample run : Java Program. Java Program

Java Programming: From Problem Analysis to Program Design, Second Edition27 Example2 public class Example3_7 { public static void main (String[] args) { int num = 763; double x = ; String str = "Java Program."; System.out.println(" "); System.out.printf("%-5d%-7.2f%-15s ***%n", num, x, str); System.out.printf("%-15s%-6d%- 9.2f ***%n", str, num, x); }

Java Programming: From Problem Analysis to Program Design, Second Edition28 Example2 Sample Run : Java Program. *** Java Program ***

Java Programming: From Problem Analysis to Program Design, Second Edition29 Formatting Output with printf

Java Programming: From Problem Analysis to Program Design, Second Edition 30 Commonly Used Escape Sequences