1 Chapter 2: Java Fundamentals cont’d Spring Lory Al Moakar

2 Outline  2.1 The Parts of a Java Program  2.2 The print and println Methods, and the Java Standard Class Library  2.3 Variables and Literals  2.4 Primitive Data Types  2.5 Arithmetic Operators  2.6 Combined Assignment Operators  2.7 Conversion Between Primitive Types  2.8 Creating Named Constants with final  2.9 The String Class  2.10 Scope  2.11 Comments  2.12 Programming Style  2.13 Reading Keyboard Input  2.14 Dialog Boxes  2.15 Common Errors to Avoid

3 Review  Parts of the program Comments: start with //  Are ignored by the compiler Class header : public class Name Method header: public static void main( String args[] ) Statements

4 Review  System.out.print: displays on the screen what we put in “”  System.out.println: same as print except that it moves the cursor to a new line after displaying the text

5 Review Moves the cursor to \n a new line \t the next tab stop \b one character back \r To the beginning of the line \\ Prints a backslash \’ Prints a single quote \” Prints a double quotation mark

6 Review  Variables: Declare: type and identifier Initialize: give it value ~ literal  Literals:  Identifiers: Start with letter, _, or $ Have only numbers, letters, _ and $ Cannot be a keyword

7 Printing a variable  2 ways: On its own: System.out.println( identifier); Combined with text: System.out.println( “The result is: “+ identifier );

8 Example // This program has a variable. public class Variable { public static void main(String[] args) { int value; value = 5; System.out.print("The value is "); System.out.println(value); }

9 2.4 Primitive Data Types  Each variable has a data type which is the type of data that can be stored in the memory location allocated  Here is a list of primitive(numeric) data types:

Primitive Data Types cont’d Data type SizeRange byte1 byteInteger between -128 to 127 short2 bytesInteger between to int4 bytesInteger between to long8 bytesInteger between to float4 bytesFloating point numbers with 7 digits of accuracy double8 bytesFloating point numbers with 15 digits of accuracy No digits after decimal point 15 digits after decimal point 7 digits after decimal point

11 Declaration revisited  Datatype Variablename;  Examples: int hours; byte minutes; short month; float average; double distance

12 The Integer Data Types // This program has variables of several of the integer types. public class IntegerVariables{ public static void main(String[] args) { int checking; // Declare an int variable named checking. byte miles; // Declare a byte variable named miles. short minutes; // Declare a short variable named minutes. long days; // Declare a long variable named days. checking = -20; miles = 105; minutes = 120; days = ; System.out.println("We have made a journey of " + miles + " miles."); System.out.println("It took us " + minutes + " minutes."); System.out.println("Our account balance is $" + checking); System.out.println("About " + days + " days ago Columbus " + "stood on this spot."); } We have made a journey of 105 miles. It took us 120 minutes. Our account balance is $-20. About days ago Columbus stood on this spot. No Commas

13 The Floating Data Types // This program demonstrates the double data type. public class Sale { public static void main(String[] args) { double price, tax, total; price = 29.75; tax = 1.76; total = 31.51; System.out.println("The price of the item " + "is " + price); System.out.println("The tax is " + tax); System.out.println("The total is " + total); } The price of the item is The tax is 1.76 The total is 31.15

14 The Floating Data Types  float number = 23.5;  float number = 23.5f;  float number = 23.5F; ERROR CORRECT

15 The boolean Data Type  a boolean variable can have two values: true false  Example: boolean bool; bool = true; System.out.println(bool); bool = false; System.out.println(bool); true false

16 The char Data Type  used to store characters  character literals are enclosed in single quotes  Example: char letter; letter = 'A'; System.out.println(letter); letter = 'B'; System.out.println(letter); ABAB

17 The char Data Type  Characters are internally represented by numbers.  Java uses Unicode which is a set of numbers that are used as codes for representing characters  The codes are found in appendix A on the CD

18 Example char letter; letter = 65; System.out.println(letter) letter = 66; System.out.println(letter); ABAB

19 Variable Assignment and Initialization  assignment statement is used to put a value into a variable. Ex: x = 15;  always put the identifier on the left of the equal sign and the literal to the right of the equal sign. Ex: 15 = x; is incorrect  you can assign the value of one identifier to another. Ex: x = y; now x has the value stored in y

20 Valid Variable Declaration  int month =2, days = 28;  float distance = 35.2f;  int c = 8, y =10, x, v=2;

Arithmetic Operators  3 types of operator: unary: require a single operand.  There is one unary operand: -9 (the negation operator)  --5 is 5 binary: require two operands ternary: require three operands

22 Arithmetic operators Operator MeaningTypeExample +AdditionBinarytotal = cost+tax; -SubtractionBinarycost = total-tax; *MultiplicationBinaryTax = cost*rate; /DivisionBinarysaleprice=original/2 ; %ModulusBinaryremainder=value% 3;

23 Examples of Statements with Arithmetic Operators  amount = x + y;  amount = ;  Minutes = 800 – call;  Tip = bill * 0.18;  Slice = cake /8; Notice that the identifier is to the left of the = Notice that the arithmetic operator is to the right of the =

24 Example int counter = 0; //counter =0 counter = counter + 1; //counter =1 counter = counter + 39; //counter=40 counter = counter – 8; //counter=32 counter = counter * 5; //counter=160 counter = counter / 2; //counter= 80

25 The % operator  Returns the remainder of the division  Examples; 4%5 is 4 30%6 is 0 22%7 is %100 is %10 is 5

26 Exercise  Write the following in a Java file: double amount = 137/5; System.out.println(“Amount is : “ + amount ); amount = 137.0/5; System.out.println(“Amount is : “ + amount );

27 Integer Division  Dividing an integer by an integer gives an integer  the remainder is ignored  Examples: 5/4 is 1 17/3 is 5

28 Operator Precedence  What is the result of:  Polynomial = 1+2*3+ 6/2 -2;  Is it ? (1+2)*3 + 6/(2-2) 1+(2*3) +(6/2)-2 (1+2)*3 + (6/2)-2

29 Precedence Rules  Always evaluate *, / and % before + and –  Always negate before any calculations  *, / and % have same precedence  + and – have same precedence  If equal precedence then evaluate from left to right except for negations where we evaluate from right to left

30 Precedence examples  Polynomial = 1+2*3+ 6/2 – 2; Polynomial has the value of =8  Polynomial = –1 + 5 – 2; // 2  Polynomial = –(–3) + –(–5); //8

31 Grouping with parentheses  You can use parentheses to force the evaluation of a formula  Examples: x * ( y + z*z ) instead of x*y + z*z x * ( y * ( z ) + 85 ) – 65 Average = (a +b +c ) /3;

32 The Math class  value = Math.pow( x,y); // now value holds x to the power of y  value = Math.sqrt( x); //now value holds the square root of x

33 Combined Assignment Operators +=x += 1;x = x + 1; –=x –= 1;x = x – 1; *=x *= 1;x = x * 1; /=x /= 1;x = x / 1; %=x %= 1;x = x % 1;