1. INTERMEDIATE PROGRAMMING USING JAVA
CS-0401
INTERMEDIATE PROGRAMMING USING JAVA
Prof. Dr. Paulo Brasko Ferreira
Fall 2016
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2. Precedence and Associativity
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3. Precedence and Associativity
2 + 3 * 4 = ?
a) 20
= ?
b) 14
2 + 3 * 4 = ?
= ?
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4. Precedence and Associativity
Precedence indicates the order in which operators are applied in an expression
Associativity indicates the order in which operands are accessed given operators of the same precedence
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7. More Operators See example: ex3.java
Java has a number of convenience operators
Allow us to do operations with less typing
Ex:
X = X + 1; is equivalent to X++;
Y = Y – 5 ; is equivalent to Y –= 5;
Z *=2;
Z /= 365;
Note: prefix and postfix versions of the unary operators
X++; ++X;
See example: ex3.java
When used as shown above, the operators have the same effect. However, when used as part of another expression there is a difference:
The postfix operator is performed AFTER the previous value is used in the expression
The prefix operator is performed BEFORE the value is used in the expression
So for example:
X = 5;
Y = X++; // Now Y is 5 and X is 6
Y = ++X; // Now Y is 6 and X is 6
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8. Ways of entering data into your program
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9. Store data via Identifiers and Variables
Get data in
Your program
Control Structures
Get data out
Statements and
Expressions
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10. Let’s play Family Feud Game
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11. What are the most common ways of entering data into a program?
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12. Hard-coded input
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13. Hard-coded inputs Good or bad? Math.PI
import java.lang.*; public class AddNumbers { public static void main(String[] args) { double a = 3; double b = 4; double c; c = a + b; System.out.println(c); } }
Good or bad?
Math.PI
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14. Input Data Using Dialog Boxes
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15. Dialog Boxes
A dialog box is a small graphical window that displays a message to the user or requests input.
A variety of dialog boxes can be displayed using the JOptionPane class.
The JOptionPane class provides methods to display each type of dialog box.
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16. The JOptionPane Class
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17. Input Dialogs
String name;
name = JOptionPane.showInputDialog("Enter your name.");
The argument passed to the method is the message to display.
If the user clicks on the OK button, name references the string entered by the user.
If the user clicks on the Cancel button, name references null.
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18. Converting a String to a Number
The JOptionPane’s showInputDialog method always returns the user's input as a String
Numbers are not Strings! Is there a problem in this case?
Names are Strings, so we are OK
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19. You can chat and interact with this person
This is John!
You can chat and interact with this person
This is John’s picture!
You cannot chat with it!
Even though they look the same, they are two different things! You cannot interact with John’s picture as you would with the actual John!
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20. Converting a String to a Number
Similarly, a String representing a number is NOT the same as a number!
You cannot do math operations on a “picture” of a number
You MUST convert the String representation to an actual number!
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21. The Parse Methods // Store 1 in bVar. byte bVar = Byte.parseByte("1");
// Store 2599 in iVar.
int iVar = Integer.parseInt("2599");
// Store 10 in sVar.
short sVar = Short.parseShort("10");
// Store in lVar.
long lVar = Long.parseLong("15908");
// Store 12.3 in fVar.
float fVar = Float.parseFloat("12.3");
// Store in dVar.
double dVar = Double.parseDouble("7945.6");
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22. The main(String[] args)
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23. The main(String[] args)
public static void main(String[] args) {
double a = Double.parseDouble(args[0]);
double b = Double.parseDouble(args[1]);
double c = a + b;
System.out.println("Value of c: " + c); }
What does “args” stand for?
But what arguments???
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24. The main(String[] args)
 Arguments from the command line
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25. How to specify Args in NetBeans
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26. Getting data from a text file
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27. Getting data from a text file
Your program must process this data
This data is saved in a text file
There are 1000 lines to process
It is inefficient to type them in the command line!
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28. Getting data from a text file
BufferedReader reader = new BufferedReader(new FileReader("/path/to/file.txt"));
String line = null;
while ((line = reader.readLine()) != null) {
// ... }
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29. Getting Data From Terminal Window
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30. The Scanner Class
To read input from the keyboard we can use the Scanner class.
The Scanner class is defined in java.util, so we will use the following statement at the top of our programs: import java.util.Scanner;
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31. The Scanner Class Scanner objects work with System.in
To create a Scanner object: Scanner keyboard = new Scanner(System.in);
See example: ex4.java.
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32. Control Structures
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33. Store data via Identifiers and Variables
Get data in
Your program
Control Structures
Get data out
Statements and
Expressions
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34. Control Statements
One of the most important types of statements in programming is the control statement
Allows 2 very important types of execution
Conditional execution
Statements may or may not execute
Iterative execution
Statements may execute more than one time
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35. Control Statements Linear Execution Conditional Execution
Iterative Execution
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36. Conditional Execution
The IF statement
The SWITCH statement
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37. What Boolean expressions could provide “true” or “false” values?
The if Statement
if (condition is true) execute next statement
What Boolean expressions could provide “true” or “false” values?
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38. if Statements and Boolean Expressions
double x = 10, y = 5, z = 10;
if (x > y)
System.out.println("X is greater than Y");
if(x == z)
System.out.println("X is equal to Y");
if(x != y) {
System.out.println("X is not equal to Y");
x = y;
System.out.println("However, now it is."); }
Example: ex5a.java
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39. Flowcharts IF statements can be modeled as a flow chart.
if (temp < 45)
System.out.println(“wear coat”);
Wear a coat.
Yes
temp < 45? No
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40. Flowcharts A block if statement may be modeled as:
Wear a coat.
Yes
temp < 45?
Wear a hat.
Wear gloves.
if (coldOutside) {
wearCoat();
wearHat();
wearGloves(); }
Note the use of curly
braces to block several
statements together.
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41. The IF-ELSE statement
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42. if-else Statements
The if-else statement adds the ability to conditionally execute code when the if condition is false.
if (expression)
statementOrBlockIfTrue;
else
statementOrBlockIfFalse;
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43. if-else Statement Flowcharts
Wear a coat.
Yes
Is it cold
outside?
Wear shorts. No
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44. Nested IF statements
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45. Nested if Statement Flowcharts
Wear a jacket
Yes
Is it cold
outside?
Wear shorts
Is it
snowing?
Wear a parka No
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46. Nested if Statements if (coldOutside) { if (snowing) { wearParka(); }
else {
wearJacket();
wearShorts();
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47. if-else-if Statements
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48. if-else-if–else Statements
if (expression_1) {
statement;
etc. }
else if (expression_2) {
…  
else {
If expression_1 is true these statements are executed, and the rest of the structure is ignored.
Otherwise, if expression_2 is true these statements are executed, and the rest of the structure is ignored.
These statements are executed if none of the expressions above are true.
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49. if-else-if Flowchart
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50. Relational and Logical Operators
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51. Relational Operators
Relational operators
Used to compare (i.e. relate) two primitive values
Result is true or false based on values and the comparison that is asserted
Ex: 6 < true because 6 IS less than 10
7 != false because 7 IS NOT equal to 7
Java has 6 relational operators < <= > >= == !=
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52. Logical Operators logical operators: ! && ||
Operate on boolean values, generating a new boolean value as a result
! && || A B
true
false !A
false
true
A&&B
true
false
A||B
true
false
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53. Boolean Expressions Let’s look at some examples Example: ex5b.java
int i = 10, j = 15, k = 20;
double x = 10.0, y = , z = 100.0;
i < j || j < k && x <= y
(i / 3) == y
(x / 3) == y
!(x != i)
Note: Precedence in boolean expressions:
relational operators !
&& ||
Examples:
True, due to the higher precedence of && over ||
False, due to integer division
False, due to precision issues with floating point numbers
True – mixed expressions are cast to the more “precise” type, so i is cast into a double
Example: ex5b.java
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54. Other ways of getting a boolean value
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55. Other ways of getting boolean values
Methods can return true and false
String.equals( ) (returns true or false)
We can use this return inside the IF statement
if (name.equals(“John”)) {
printHisProfile(); }
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56. The switch Statement
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57. The switch Statement
switch(Expression) { case CaseExpression1: // place one or more statements here break; case CaseExpression2: // case statements may be repeated //as many times as necessary default: }
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58. The case Statement The break statement ends the case statement.
The break statement is optional.
If a case does not contain a break, then program execution continues into the next case.
The default section is optional and will be executed if no CaseExpression matches the SwitchExpression
See Ex6.java and Ex6b.java
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59. Any Questions?
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