Chapter 2 topics

1. Chapter 2 topics

2. println & print System.out.println(“ Will print this statement and then return to a new line”); System.out.print( “Will print this statement and stay on the same line” ); System.out.println(“ I’m on the line with the statement above.”);

3. // ************************************************************************ // PrintPrintln.java Author: Gail Chapman // This program demonstrates Println and Print // *********************************************************************** public class PrintPrintln { public static void main(String[]args) { System.out.println("Will print this statement and then return to a new line"); System.out.print( "Will print this statement and stay on the same line" ); System.out.println(" I’m on the line with the statement above."); } } Output: Will print this statement and then return to a new line Will print this statement and stay on the same line I’m on the line with the statement above.

4. String literals & Concatenation String refers to a string of characters that make up words. String is a class. It is not a primitive data type. Every String literal is an object. String literals are words in quotation marks. “This is a String literal”;

5. Concatenation The concatenation operator used with Strings is the plus sign + The + sign is also used for arithmetic operations. The + sign joins: Strings and other Strings (“This is a String ” + “ and another String”);

6. Strings & Numbers Need to be careful to get correct output from numbers. System.out.println(“We want to add “ + 10 + 15); What is the output: The compiler starts at the left encounters the String and reads everything after it as a String. It will perform String concatenation. Output: We want to add 1015 10 and 15 are printed as if they are String literals.

7. Strings & Numbers The plus sign is also used as the addition operator. System.out.println(36 + 4 + “ is 36 + 4”); The numbers will be added together because they are at the beginning before the String. So it will perform addition. Output: 40 is 36 + 4.

8. Strings and Numbers You can use parentheses to force addition with the + sign. System.out.println(“36 + 5 = “ + (36+5)); Parentheses have highest precedence so it performs that operation first. Output: 36 + 5 = 40

9. What will print? System.out.println("12" + 3 + 4); System.out.println("12" + (3 + 4)); System.out.println(12 + 3 + 4); System.out.println(12 + "3" + 4); System.out.println(12 + 3 + "4"); 1234 127 19 1234 154

10. Check Printing String literals with concatenation What will the following print? System.out.println(“This will print “ + 3 + 2 + 0); System.out.println(“This will print “ + (3 + 2 + 0)); System.out.println(3 + 2 + 0 + “ will print”); System.out.println(“This will print “ + 2 * 6); This will print 320 This will print 5 5 will print This will print 12

11. public class ConcatenationRules { public static void main(String[]args) { System.out.println("This will not add the numbers 10 + 15 together " + 10 + 15 ); System.out.println(36 + 4 + " will be the sum of 36 + 4"); System.out.println("This will add 36 + 4 because of the ( ) " + (36+4)); } } Output: This will not add the numbers 10 + 15 together 1015 40 will be the sum of 36 + 4 This will add 36 + 4 because of the ( ) 40 >

12. Escape sequences Page 60 • Used with Strings to produce a newline, slash or quotation marks. \t tab will tab 5 spaces \n newline will go to a new line \\ will print \ will print one slash \” will print double quotes

13. Escape Sequences //escape characters public class Escape { public static void main(String[]args) { System.out.println("A slash n \nis used to go to a new line\n"); System.out.println("A slash quotation mark \"will\" print a double quote"); System.out.println("double slash \\ will print one backslash."); System.out.println("A slash t twill tab.\n\tName\t\tAge\t\tDOB"); System.out.println("A slash one quotation \'will\' produce single quote."); } }

14. PRIMITIVE DATA TYPES: Information in program is stored in variables. Data type is the type of data stored in the variable. There are 8 Primitive data types in Java.

15. Memory Storage • In order to reserve space in memory for the variable, the computer has to know what type of data it will be. • Declare = to tell what type of data the variable will hold and its name • Initialize = assign the variable a value using the = sign

16. Declare is to tell what type of data the variable will hold and its name • the computer needs to know how much memory to store for that variable int number; double money; boolean done; You cannot use a variable until you declare the type Initalize is to assign the variable a value using the = sign number = 4; money = 7.50; done = false ; Can Initialize & Declare at same time int number = 37; double money = 28.42; boolean done = true;

17. data type with operations • when you use 2 integers in an operation the result is an integer • 20/6 + 3 = 20/6 = 3 + 3 = 6 • When you use a double as one of the operands then the result is a double • 20/6.0 + 3 = 20/6.0 = 3.333 + 3 = 6.333

18. Using variables to store the answer Storing that information in a variable • integers can be stored in an int or a double int a = 20; int b = 6 int c = 3; int d; double d; 20/6 + 3 = 6.0; d = a / b + c ; 20/6 + 3 = 6

19. data type variable name Variables • A variable is a name for a location in memory • A variable must be declared by specifying the variable's name and the type of information that it will hold int total; int count, temp, result; Multiple variables can be created in one declaration

20. Variables • A variable can be given an initial value in the declaration. Called initializing. int sum = 0; int base = 32, max = 149; double amount = 47.52; boolean done = false; public class PianoKeys { //----------------------------------------------------------------- // Prints the number of keys on a piano. //----------------------------------------------------------------- public static void main (String[] args) { int keys = 88; System.out.println ("A piano has " + keys + " keys."); } } • When a variable is referenced in a program, its current value is used • See PianoKeys.java

21. Assignment • An assignment statement changes the value of a variable • The assignment operator is the = sign int total = 55; total = 47; • The expression on the right is evaluated and the result is stored in the variable on the left • The value that was in totalinitially is overwritten • You can assign only a value to a variable that is consistent with the variable's declared type could not say total = 47.50 because total is declared as an int; • See Geometry.java (page 70)

22. //********************************************************************//******************************************************************** // Geometry.java Author: Lewis/Loftus/Cocking // // Demonstrates the use of an assignment statement to change the // value stored in a variable. //******************************************************************** public class Geometry { //----------------------------------------------------------------- // Prints the number of sides of several geometric shapes. //----------------------------------------------------------------- public static void main (String[] args) { int sides = 7; // declaration with initialization System.out.println ("A heptagon has " + sides + " sides."); sides = 10; // assignment statement System.out.println ("A decagon has " + sides + " sides."); sides = 12; System.out.println ("A dodecagon has " + sides + " sides."); } • }