Chapter 2: Java Fundamentals cont’d

1. Chapter 2: Java Fundamentals cont’d Spring 2006-2007 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

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:

10. 2.4 Primitive Data Types cont’d No digits after decimal point 7 digits after decimal point 15 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 = 185000; 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 185000 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 29.75 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 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); A B

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); A B

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;

21. 2.5 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

23. Examples of Statements with Arithmetic Operators • amount = x + y; • amount = 562+543; • 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 1 • 3205%100 is 5 • 3205%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 1+6+3-2=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 + 165 ) + 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