Chapter 2 – Continued Basic Elements of Java

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

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Chapter Objectives

Variables – Cont. Type Conversion String Class Commonly Used String Methods Parsing Numeric Strings

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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. 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

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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

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Type Conversion (Casting)

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

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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 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”

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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

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Strings and the Operator + Operator + can be used to concatenate two

strings, or a string and a numeric value or character.

Example

String str;

int num1, num2;

num1 = 12;

num2 = 26;

str = "The sum = " + num1 + num2;

After this statement executes, the string assigned to str is:

"The sum = 1226";

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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";

Strings and the Operator +

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

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

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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

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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.

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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

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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

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Chapter 2 – Continued Basic Elements of Java

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