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Chapter 2 – Continued Basic Elements of Java

Chapter 2 – Continued Basic Elements of Java. Chapter Objectives. Type Conversion String Class Commonly Used String Methods Parsing Numeric Strings Commonly Used Escape Sequences. Type Conversion (Casting). Used: to change one data type to another . to avoid implicit type coercion.

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Chapter 2 – Continued Basic Elements of Java

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  1. Chapter 2 – Continued Basic Elements of Java

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

  3. 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

  4. Type Conversion (Casting) Examples: (int)(7.9 + 6.7) = 14 (int)(7.9) + (int)(6.7) = 13 (double)(17) = 17.0 (double)(8+3) = (double)11 = 11.0 (double)(7) /2 = 7.0/2 = 3.5 (double)(7/2) = 3.0 (int)(7.8+(double)(15)/2) = (int)15.3 =15 Java Programming: From Problem Analysis to Program Design, Second Edition

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

  6. The classString 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

  7. The classString 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” Java Programming: From Problem Analysis to Program Design, Second Edition 7

  8. The classString 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

  9. Some Commonly Used String Methods Java Programming: From Problem Analysis to Program Design, Second Edition 9

  10. Some Commonly Used String Methods Java Programming: From Problem Analysis to Program Design, Second Edition 10

  11. Some Commonly Used String Methods Java Programming: From Problem Analysis to Program Design, Second Edition 11

  12. Some Commonly Used String Methods Java Programming: From Problem Analysis to Program Design, Second Edition 12

  13. 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 Edition 13

  14. 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 14

  15. Input Reading a Single Character if ch is a charvariable. To input A into ch, you can use the following statement: ch = console.next().charAt(0); 15 Java Programming: From Problem Analysis to Program Design, Second Edition

  16. 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 classInteger, which converts a numeric integer string into a value of the type int. • parseFloat is a method of the classFloat and is used to convert a numeric decimal string into an equivalent value of the type float. • parseDouble is a method of the classDouble, 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 Edition 16

  17. 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 Edition 17

  18. 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") = 34.56 • Float.parseFloat("-542.97") = -542.97 • 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") = 345.78 • Double.parseDouble("-782.873") = -782.873 Java Programming: From Problem Analysis to Program Design, Second Edition 18

  19. 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 Edition 19

  20. 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 Edition 20

  21. 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 =59.05511811023 The o/p would be : There are 59.06 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 Edition 21

  22. Example1 public class Example3_6 { public static void main (String[] args) { int num = 763; double x = 658.75; String str = "Java Program."; System.out.println("123456789012345678901234567890"); 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 Edition 22

  23. Example1 Sample run : 123456789012345678901234567890 763 658.75 Java Program. Java Program. 763 658.75 Java Programming: From Problem Analysis to Program Design, Second Edition 23

  24. Example2 public class Example3_7 { public static void main (String[] args) { int num = 763; double x = 658.75; String str = "Java Program."; System.out.println("123456789012345678901234567890"); 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 Edition 24

  25. Example2 Sample Run : 123456789012345678901234567890763 658.75 Java Program. ***Java Program. 763 658.75 *** Java Programming: From Problem Analysis to Program Design, Second Edition 25

  26. Formatting Output with printf Java Programming: From Problem Analysis to Program Design, Second Edition 26

  27. Commonly Used Escape Sequences 27 Java Programming: From Problem Analysis to Program Design, Second Edition

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