Chapter 2 – Continued Basic Elements of Java. Chapter Objectives Type Conversion String Class...

Chapter 2 – Chapter 2 – ContinuedContinued Basic Elements of Basic Elements of JavaJava

Chapter Objectives

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

Java Programming: From Problem Analysis to Program Design, Second Edition 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

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

Type Conversion (Casting)

8. (int)(‘A’) = 65 9. (int)(‘8’) = 5610. (char)(65) = ‘A’ 11. (char)(56) = ‘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 .

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

Some Commonly Used String Methods

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

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

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);

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.

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

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

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.

Formatting Output with printfSystem.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.

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.

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); } }

Example1

Sample run :123456789012345678901234567890

763 658.75 Java Program. Java Program. 763 658.75

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); }}

Example2

Sample Run : 123456789012345678901234567890

763 658.75 Java Program. ***Java Program. 763 658.75 ***

Formatting Output with printf

Commonly Used Escape Sequences

Chapter 2 – Continued Basic Elements of Java. Chapter Objectives Type Conversion String Class...

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