Lecture 3.1: Operator Precedence and Eclipse Tutorial Michael Hsu CSULA

Clarifications for Lecture 3  a % b  If a > b, then it returns the remainder of the division  If a < b, then it returns a  If a == b, then it returns 0  Testing even and odd  If x is even, then x % 2 == 0 evaluates to true  If x is odd, then x % 2 == 1, or you can use x % 2 != 0

More Clarifications  Recall the fun example: int i =10; int k = i+++i; System.out.println(k);  Why is k == 21?

Expressions, Literals, and Statements  Literals:  Source code representation of a fixed value  Examples:  1, 2, 0, -200, true, false, ‘A’  Expression:  Made up of variables, operators, that evaluates to a single value  Java subexpressions are evaluated left to right  Examples:  2 * 3 * 4  2 % 3  i+++I  K =10 Source:

Statements  “sentences” with semi colons at the end  Assignment  Any Use of ++ or –  You will lean different types later

Operator Precedence In Java  Some key words:  Precedence Order:  When two operators share an operand the operator with the higher precedence goes first  Example: * 3 is the same as 1 + (2 * 3)  Associativity:  When an expression has two operators with the same precedence, the expression is evaluated according to its associativity  Example: x = y = z= 17 is evaluated as x = ( y= (z = 17)), because = operator has right to left associativity Source:

Precedence and Associativity Table 

So how does i+++i work? int i =10; int k = i+++i; System.out.println(k);  i+++i is equivalent to (i++)+i, since ++ has precedence over +  We evaluate from left to right  Since it is post increment, i++ evaluates to 10, (10) + i  After i++ is evaluated, we increment i so i becomes 11  = 21

Using variables in String literals  We did System.out.println() with String literals inside:  System.out.println(“2 divided by 3 in java is zero”);  To use variables in String literals, use the + operator: int num1 = 2; int num2 = 3; System.out.println(num1+ " divided by "+num2+" in Java is " + 2/3);

Eclipse Tutorial  Follow the eclipse setup guide in the resources section on the course website  Key terms:  Workspace  Your working directory  it will contain multiple projects  When you want to move your eclipse files from file explorer, move the entire workspace folder.  Projects  This is where you will put your java files  You can have one workspace for all your courses, and have different projects for each course, or have separate workspaces for each course and have separate projects for each assignments  I recommend having a different workspace for each of your courses with separate projects for each assignment of the course  Makes your life easier

Useful Eclipse Tips  Show Line Numbers:  Window -> Preferences -> expand General -> expand Editors -> click on Text Editors -> check show line numbers  Ctrl+ SPACE  Autocomplete, auto fix  Ctrl + SHIFT + f  Auto format and indentation  Ctrl + d  Delete entire line  Right click on a variable then click refactor  You can rename your variables and Eclipse will update all the occurrences for you

DO NOT delete files in your eclipse workspace from file explorer  Eclipse uses special files to track how your project directory is set up, your interface layout, etc.  Do everything from within eclipse so you don’t screw up your projects  I’ll try to put up an step by step tutorial on the course webpage