© 2007 Pearson Addison-Wesley. All rights reserved2-1 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 reserved2-2 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 reserved2-3 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 reserved2-4 Escape Sequences Some Java escape sequences: See Roses.java (page 66)Roses.java Escape Sequence \b \t \n \r \" \' \\ Meaning backspace tab newline carriage return double quote single quote backslash

© 2007 Pearson Addison-Wesley. All rights reserved2-5 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 reserved2-6 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 reserved2-7 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 reserved2-8 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 Addition Subtraction Multiplication Division Remainder +-*/%+-*/%

© 2007 Pearson Addison-Wesley. All rights reserved2-9 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 % 3 equals 8 % 12 equals 2 8

© 2004 Pearson Addison-Wesley. All rights reserved4-10 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 reserved4-11 More Objects Here is another example of a class:  class Window {... } Here are some examples of Windows:

© 2004 Pearson Addison-Wesley. All rights reserved4-12 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 reserved4-13 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 reserved7-14 Arrays An array is an ordered list of values An array of size N is indexed from zero to N-1 scores The entire array has 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 reserved7-15 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 reserved7-16 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 BasicArray.java

© 2004 Pearson Addison-Wesley. All rights reserved7-17 //******************************************************************** // 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 + " "); } }