© 2007 Pearson Addison-Wesley. All rights reserved 2-1

Character Strings

• A string of characters can be represented as a string literal by putting double quotes around the text:

• Examples:

"This is a string literal.""123 Main Street""X"

• Every character string is an object in Java, defined by the String class

• Every string literal represents a String object

© 2007 Pearson Addison-Wesley. All rights reserved 2-2

String Concatenation

• The string concatenation operator (+) is used to append one string to the end of another

"Peanut butter " + "and jelly"• It can also be used to append a number to a string• A string literal cannot be broken across two lines

in a program

© 2007 Pearson Addison-Wesley. All rights reserved 2-3

String Concatenation• The + operator is also used for arithmetic addition

• The function that it performs depends on the type of the information on which it operates

• If both operands are strings, or if one is a string and one is a number, it performs string concatenation

• If both operands are numeric, it adds them

• The + operator is evaluated left to right, but parentheses can be used to force the order

© 2007 Pearson Addison-Wesley. All rights reserved 2-4

Escape Sequences

• Some Java escape sequences:

• See Roses.java (page 66)

Escape Sequence

\b\t\n\r\"\'\\

Meaning

backspacetabnewlinecarriage returndouble quotesingle quotebackslash

© 2007 Pearson Addison-Wesley. All rights reserved 2-5

Primitive Data• There are eight primitive data types in Java

• Four of them represent integers: byte, short, int, long

• Two of them represent floating point numbers: float, double

• One of them represents characters: char

• And one of them represents boolean values: boolean

© 2007 Pearson Addison-Wesley. All rights reserved 2-6

Characters

• A char variable stores a single character

• Character literals are delimited by single quotes:'a' 'X' '7' '$' ',' '\n'

• Example declarations:

char topGrade = 'A';

char terminator = ';', separator = ' ';

• Note the distinction between a primitive character variable, which holds only one character, and a String object, which can hold multiple characters

© 2007 Pearson Addison-Wesley. All rights reserved 2-7

Boolean

• A boolean value represents a true or false condition

• The reserved words true and false are the only valid values for a boolean type

boolean done = false;

• A boolean variable can also be used to represent any two states, such as a light bulb being on or off

© 2007 Pearson Addison-Wesley. All rights reserved 2-8

Expressions• An expression is a combination of one or more

operators and operands• Arithmetic expressions compute numeric results and

make use of the arithmetic operators:

• If either or both operands used by an arithmetic operator are floating point, then the result is a floating point

AdditionSubtractionMultiplicationDivisionRemainder

+-*/%

© 2007 Pearson Addison-Wesley. All rights reserved 2-9

Division and Remainder

• If both operands to the division operator (/) are integers, the result is an integer (the fractional part is discarded)

• The remainder operator (%) returns the remainder after dividing the second operand into the first

14 / 3 equals

8 / 12 equals

4

0

14 % 3 equals

8 % 12 equals

2

8

© 2004 Pearson Addison-Wesley. All rights reserved 4-10

Classes and Objects• A Java program consists of one or more

classes• A class is an abstract description of objects• Here is an example class:

class Dog { ...description of a dog goes here... }

• Here are some objects of that class:

© 2004 Pearson Addison-Wesley. All rights reserved 4-11

More Objects• Here is another example of a class:

class Window { ... }• Here are some examples of Windows:

© 2004 Pearson Addison-Wesley. All rights reserved 4-12

Classes contain data definitions• Classes describe the data held by each of its

objects• Example:

class Dog { String name; int age; ...rest of the class...}

Data usually goes first in a class

• A class may describe any number of objects Examples: "Fido", 3; "Rover", 5; "Spot", 3;

• A class may describe a single object, or even no objects at all

© 2004 Pearson Addison-Wesley. All rights reserved 4-13

Classes contain methods• A class may contain methods that describe the behavior of

objects• Example:

class Dog { ... void bark() { System.out.println("Woof!"); }}

Methods usually go after the data

• When we ask a particular Dog to bark, it says “Woof!”• Only Dog objects can bark; the class Dog cannot bark

© 2004 Pearson Addison-Wesley. All rights reserved 7-14

Arrays

• An array is an ordered list of values

0 1 2 3 4 5 6 7 8 9

79 87 94 82 67 98 87 81 74 91

An array of size N is indexed from zero to N-1

scores

The entire arrayhas a single name

Each value has a numeric index

This array holds 10 values that are indexed from 0 to 9

© 2004 Pearson Addison-Wesley. All rights reserved 7-15

Arrays• For example, an array element can be assigned a

value, printed, or used in a calculation:

scores[2] = 89;

scores[first] = scores[first] + 2;

mean = (scores[0] + scores[1])/2;

System.out.println ("Top = " + scores[5]);

© 2004 Pearson Addison-Wesley. All rights reserved 7-16

Using Arrays• The iterator version of the for loop can be used

when processing array elements

for (int score : scores) System.out.println (score);

• This is only appropriate when processing all array elements from top (lowest index) to bottom (highest index)

• See BasicArray.java

© 2004 Pearson Addison-Wesley. All rights reserved 7-17

//********************************************************************// BasicArray.java // Demonstrates basic array declaration and use.//********************************************************************

public class BasicArray{ //----------------------------------------------------------------- // Creates an array, fills it with various integer values, // modifies one value, then prints them out. //----------------------------------------------------------------- public static void main (String[] args) { final int LIMIT = 15, MULTIPLE = 10;

int[] list = new int[LIMIT]; // Initialize the array values for (int index = 0; index < LIMIT; index++) list[index] = index * MULTIPLE; list[5] = 999; // change one array value // Print the array values for (int value : list) System.out.print (value + " "); }}