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