Chapter 2: Java Fundamentals Type conversion,String.
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Transcript of Chapter 2: Java Fundamentals Type conversion,String.
Chapter 2: Java Fundamentals
Type conversion ,String
Chapter Objectives
Type ConversionString ClassCommonly Used String MethodsParsing Numeric StringsCommonly Used Escape Sequences
Variables – Cont.
FloatThe default type of floating point numbers is double .The declaration :
float rate = 15.5f ; without the f , the compiler will generate an error
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Variables – Cont.
CharWhen 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)
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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
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Type Conversion (Casting)
Examples:1. (int)(7.9 + 6.7) = 142. (int)(7.9) + (int)(6.7) = 133. (double)(17) = 17.04. (double)(8+3) = (double)11 = 11.05. (double)(7) /2 = 7.0/2 = 3.56. (double)(7/2) = 3.07. (int)(7.8+(double)(15)/2) =
(int)15.3 =15
Java Programming: From Problem Analysis to Program Design, Second Edition
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Type Conversion (Casting)
8. (int)(‘A’) = 65 9. (int)(‘8’) = 5610. (char)(65) = ‘A’ 11. (char)(56) = ‘8’
Java Programming: From Problem Analysis to Program Design, Second Edition
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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
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Java Programming: From Problem Analysis to Program Design, Second Edition 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
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Java Programming: From Problem Analysis to Program Design, Second Edition 12
Some Commonly Used String Methods
Java Programming: From Problem Analysis to Program Design, Second Edition 13
Some Commonly Used String Methods
Java Programming: From Problem Analysis to Program Design, Second Edition 14
Some Commonly Used String Methods
Java Programming: From Problem Analysis to Program Design, Second Edition 15
Some Commonly Used String Methods
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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 17
Examples on string methods
System.out.println(s1.substring(1 , 4)); //bcdSystem.out.println(s1 + “xyz”); // abcdefegxyzSystem.out.println( s1.replace(‘d’ ,’D’)); // abcDefegSystem.out.println(s1.charAt(4) ); // eSystem.out.println(s1.indexOf(‘b’)); // 1System.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 Edition 19
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 Edition 20
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") = 6723Integer.parseInt("-823") = -823
Java Programming: From Problem Analysis to Program Design, Second Edition 21
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") = 34.56Float.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") = 345.78Double.parseDouble("-782.873") = -782.873
Java Programming: From Problem Analysis to Program Design, Second Edition 22
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 23
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 24
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 =59.05511811023The 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.
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Example1public 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); } }
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Example1
Sample run :123456789012345678901234567890
763 658.75 Java Program. Java Program. 763 658.75
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Example2public 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 28
Example2Sample Run : 123456789012345678901234567890
763 658.75 Java Program. ***Java Program. 763 658.75 ***
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Formatting Output with printf
Java Programming: From Problem Analysis to Program Design, Second Edition 30
Commonly Used Escape Sequences