1 Characters Boolean A char variable stores a single character A - PDF document

CSC 2014 Java Bootcamp Lecture 2 Variables, Expressions, I/O & Control VARIABLES & EXPRESSIONS 2 Variables Variable Initialization  A variable is a name for a location in memory  A variable can be given an initial value in the declaration  A variable must be declared by specifying the int sum = 0; variable's name and the type of information that it will int base = 32, max = 149; hold variable name data type • When a variable is referenced in a program, its current value is used int total; int count, temp, result; Multiple variables can be created in one declara ration 3 4 Primitive Data Numeric Primitive Data  The difference between the various numeric primitive  There are eight primitive data types in Java types is their size, and therefore the values they can  Four of them represent integers: store: – byte , short , int , long  Two of them represent floating point numbers: Type Storage Min Value Max Value – float , double  One of them represents characters: 8 bits -128 128 127 127 byte – char 16 bits -32,768 32,767 short 32 bits -2,147,483,648 2,147,483,647 int  And one of them represents boolean values: long 64 bits < -9 x 10 18 < 18 > 9 x 10 18 18 – boolean 38 with 7 significant digits 32 bits +/ +/- 3.4 x 10 38 float 308 with 15 significant digits 64 bits +/ +/- 1.7 x 10 308 double 5 6 1

Characters Boolean  A char variable stores a single character  A boolean value represents a true or false condition  Character literals are delimited by single quotes:  The reserved words true and false are the only 'a' 'X' '7' '$' ',' '\n' valid values for a boolean type  Example declarations: boolean done = false; char topGrade = 'A';  A boolean variable can also be used to represent any char terminator = ';', separator = ' '; two states, such as a light bulb being on or off  Note the distinction between a primitive character variable, which holds only one character, and a String object, which can hold multiple characters 7 8 Constants Assignment  A constant is an identifier that is similar to a variable  An assignment statement changes the value of a except that it holds the same value during its entire variable existence  The assignment operator is the = sign  As the name implies, it is constant, not variable total = 55;  The compiler will issue an error if you try to change the • The expression on the right is evaluated and the value of a constant result is stored in the variable on the left  In Java, we use the final modifier to declare a • The value that was in total is overwritten constant • You can only assign a value to a variable that is final int MIN_HEIGHT = 69; consistent with the variable's declared type 9 10 Expressions Division and Remainder  If both operands to the division operator ( / ) are  An expression is a combination of one or more operators and operands integers, the result is an integer (the fractional part is discarded)  Arithmetic expressions compute numeric results and make use of the arithmetic operators: equals equals 14 / 3 4 Addition + equals equals 8 / 12 0 Subtraction - Multiplication * • The remainder operator (%) returns the remainder Division / after dividing the second operand into the first Remainder % • If either or both operands used by an arithmetic equals equals 14 % 3 2 operator are floating point, then the result is a equals equals 8 % 12 8 floating point 11 12 2

Operator Precedence Operator Precedence  Operators can be combined into complex expressions  What is the order of evaluation in the following expressions? result = total + count / max - offset; a + b + c + d + e a + b * c - d / e  Operators have a well-defined precedence which 1 2 3 4 3 1 4 2 determines the order in which they are evaluated  Multiplication, division, and remainder are evaluated a / (b + c) - d % e prior to addition, subtraction, and string concatenation 2 1 4 3  Arithmetic operators with the same precedence are evaluated from left to right, but parentheses can be a / (b * (c + (d - e))) used to force the evaluation order 4 3 2 1 13 14 Increment and Decrement Increment and Decrement  The increment and decrement operators use only one  The increment and decrement operators can be applied operand in postfix form :  The increment operator ( ++ ) adds one to its operand count++  The decrement operator ( -- ) subtracts one from its  or prefix form : operand ++count  The statement  When used as part of a larger expression, the two forms count++; can have different effects is functionally equivalent to  Because of their subtleties, the increment and count = count + 1; decrement operators should be used with care 15 16 Shortcut Assignment Operators Shortcut Assignment Operators  Often we perform an operation on a variable, and then  There are many assignment operators in Java, including store the result back into that variable the following:  Java provides assignment operators to simplify that process Operator Example Equiva valent To += x += y x = x + y  For example, the statement -= x -= y x = x - y *= x *= y x = x * y num += count; /= x /= y x = x / y %= x %= y x = x % y is equivalent to num = num + count; 17 18 3

Shortcut Assignment Operators  The right hand side of an assignment operator can be a complex expression  The entire right-hand expression is evaluated first, then the result is combined with the original variable  Therefore result /= (total-MIN) % num; is equivalent to INPUT & OUTPUT result = result / ((total-MIN) % num); 19 20 Interactive Programs Reading Input  Programs generally need input on which to operate  The following line creates a Scanner object that reads from the keyboard:  The Scanner class provides convenient methods for Scanner scan = new Scanner (System.in); reading input values of various types  The new operator creates the Scanner object  A Scanner object can be set up to read input from various sources, including the user typing values on the  Once created, the Scanner object can be used to keyboard invoke various input methods, such as:  Keyboard input is represented by the System.in object answer = scan.nextLine(); 21 22 Reading Input Input Tokens  The Scanner class is part of the java.util class  Unless specified otherwise, white space is used to library, and must be imported into a program to be used separate the elements (called tokens ) of the input  The nextLine method reads all of the input until the  White space includes space characters, tabs, new line end of the line is found characters  The next method of the Scanner class reads the next input token and returns it as a string  Methods such as nextInt and nextDouble read data of particular types 23 24 4

Example: The High-Low Game The printf Method  The System.out.printf method can be used to print formatted output to the console window  System.out is a PrintStream object double height = 24.56832; System.out.printf("The height is %.2f%n", height); The height is 24.57 25 26 The printf Method The printf Method  The printf method takes a format string followed by series  A format specifier starts with the % sign and ends with a of values that are "plugged" into the format string conversion code  The format string may contain format specifiers (such as %.2f and %n) Format Specifier Output %d decimal integer format string %f floating-point %e scientific notation System.out.printf("The height is %.2f%n", height); %c character %b boolean %s character string %.2f - print this floating-point value to two decimal places %% percent sign %n newline %n - new line (move to the next line of output) 27 28 The printf Method  The printf method accepts any number of parameters  The values must match up to the format specifiers in the format string int a = 32; double b = 123.45; System.out.printf("The sum of %d and %.3f is %.3f%n", a, b, a + b); CONTROL STRUCTURES The sum of 32 and 123.450 is 155.450 29 30 5