Understanding Java Basics: Variables, Type Conversion, and Common String Methods

1. Chapter 2 – Continued Basic Elements of Java

2. Chapter Objectives • Variables – Cont. • Type Conversion • String Class • Commonly Used String Methods • Parsing Numeric Strings

3. 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

4. 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)

6. 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

7. 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

8. Type Conversion (Casting) (int)(‘A’) = 65 (int)(‘8’) = 56 (char)(65) = ‘A’ (char)(56) = ‘8’

9. 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 .

10. 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 10

11. 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

12. Strings and the Operator + • Operator + can be used to concatenate two strings, or a string and a numeric value or character. Example String str; intnum1, num2; num1 = 12; num2 = 26; str = "The sum = " + num1 + num2; After this statement executes, the string assigned to str is: "The sum = 1226";

13. Strings and the Operator + • Consider the following statement: str = "The sum = " + (num1 + num2); • In this statement, because of the parentheses, you first evaluate num1 + num2. Because num1 and num2 are both int variables, num1 + num2 = 12 + 26 = 38. After this statement executes, the string assigned to str is: "The sum = 38";

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

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

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

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

18. 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

19. 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

20. 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

21. 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

22. 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