Transcript Ch02ZybWrapUp

Chapter 2
Wrap Up
2/18/16 & 2/22/16
Topics
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Review for Exam I
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DecimalFormat
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More Style Conventions
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Debugging using eclipse
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The Java API
Exam I
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Next week
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Th, 2/25/16
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M, 2/29/16
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Over Chapter 1, 2.1-2.6, 4.1 and 4.3, eclipse and linux
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Review material on my website
Class DecimalFormat
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Class DecimalFormat enables control of output
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In java.text package.
Specify a string pattern to describe desired format
double val = 1.23;
DecimalFormat formatter =
new DecimalFormat("0.000");
System.out.println(formatter.format(val));
Imagine! Java: Programming Concepts in Context by Frank M. Carrano, (c) Pearson Education - Prentice Hall, 2010
Class DecimalFormat
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0 – digit, leading and trailing zeros
# -- digit, no leading and trailing zeros
% -- percentage
$ -- at beginning displays dollar sign
Imagine! Java: Programming Concepts in Context by Frank M. Carrano, (c) Pearson Education - Prentice Hall, 2010
Class DecimalFormat
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Figure 4-7 Examples of
patterns used with class
DecimalFormat
Imagine! Java: Programming Concepts in Context by Frank M. Carrano, (c) Pearson Education - Prentice Hall, 2010
Previous Style Conventions
Class names begin with upper case
Method names and variable names begin with lower
case
Braces
eclipse puts open brace on the line with the heading
Line up indentation of the closing brace with whatever it is
ending.
End brace commented(optional)
Lines within braces indented
Skip lines for readability (white space)
More Conventions from 2.10
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Each statement on its own line.
A blank line can separate groups of statements, but related
statements usually have no blank lines between them.
Arithmetic operators and = separate by one space. No
space precedes an ending semicolon or ( ).
Variable/parameter names are descriptive, use at least two
words.
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exceptions for loop indices (i, j), or math items like point
coordinates (x, y).
More Conventions from 2.10
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Constants use upper case and underscores (and at least two
words)
Variables usually defined early (not within code), and initialized
to be safe (if practical).
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Lines of code are typically less than 100 characters wide.
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Look at GramsToOuncesStyle.java
Questions
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In the following program give an example of something
that is not properly named.
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Give an example of bad indentation.
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What is wrong with the println statement?
Copy This Program and Fix the Style
public class ShippingCalculator {
public static void main (String [] args) {
int shipWeightPounds = 10;
int shipCostCents;
final int FLAT_FEE_CENTS = 75 ;final int centsPerPound=25 ;
shipCostCents = FLAT_FEE_CENTS + shipWeightPounds * centsPerPound;
System.out.println("Weight(lb): " + shipWeightPounds + ", Flat fee(cents): " + FLAT_FEE_CENTS + ",
Cents per pound: " + centsPerPound + ", Shipping cost(cents): " + shipCostCents);
return;
}
}
Debugging in Eclipse 2.8
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Syntax Errors
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Caught by the Editor.
Logic Errors
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Bad Results
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Can use diagnostic prints to examine variables
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In eclipse you can exam the contents of variable
Debugging in Eclipse
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OuncesToGrams Example, 1.5 oz → 42.52 g
1)Set a break point in the program near a possible bug.
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Right click in margin left of code
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Can right click again to untoggle
2)Run the program with “Debug as”
Click yes when dialog box appears
 Gets you into Debug mode
3)Use box in upper right to examine variables.
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Debugging in Eclipse
4)Use buttons to execute one statement at a time.
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Step-into
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Step-over for java methods
5)Click “Java” on top tool bar to get back to normal mode.
Questions
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How do you toggle a breakpoint in eclipse?
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How do you get into Debug mode?
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Why would you want to examine a variable's contents?
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What is the difference between step-into and step-over?
Java API 2.7
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Google “Java API”
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Oracle owns the language.
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Use API to look up a class.
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e.g. Scanner
Can see what methods it has.
Lab
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Copy the program on slide #12 into eclipse.
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Fix style problems in the program.
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Set a break point in the above program. Use the debugger
to examine the shipCostCents variable's contents while the
program is executing.
Get into a web browser and find the Java API.
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Find the method in the String class that lets you
know the length of a String.
Exam Next Week
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Don't forget your notes!
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Good Luck!