Transcript JavaReview

Java Review
Outline
• Java Primitives, Program Structure
• Operators, Control Flow, Loops
• Classes and Objects
Most of these slides are based on
“Intro to OOP with Java” text book by C. Thomas Wu
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Java Translation
•
The Java compiler translates Java source code into a special
representation called bytecode in the .class file
•
Java bytecode is not the machine language for any specific CPU
•
Another software tool, called an interpreter (in our case the
Java Virtual Machine), executes the bytecode
•
Java is considered to be architecture-neutral
•
The Java compiler is not tied to any particular machine
2
Program Structure
//
comments about the class
public class MyProgram
{
//
comments about the method
public static void main (String[] args)
{
method body
method header
}
}
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Arithmetic Operators
Intro to OOP with Java, C. Thomas Wu
4
Operator Precedence Rules
5
Syntax for the if Statement
if ( <boolean expression> )
<then block>
else
<else block>
Boolean Expression
Can be visualized as a flowchart
if (
testScore < 70
)
JOptionPane.showMessageDialog(null,
"You did not pass" );
Then Block
else
Else Block
JOptionPane.showMessageDialog(null,
"You did pass " );
Indentation is important!
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Comparing Objects
With primitive data types, we have only one way to compare
them, but with objects (reference data type), we have two
ways to compare them.
We can test whether two variables point to the same
object (use ==), or
We can test whether two distinct objects have the same
contents.
String str1 = new String("Java");
String str2 = new String("Java");
if (str1 == str2) {
System.out.println("They are equal");
} else {
System.out.println("They are not equal");
}
Sol : They are not equal
Discussion of some string methods
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Syntax for the switch Statement
switch ( <arithmetic expression> ) {
<case label 1> : <case body 1>
…
<case label n> : <case body n>
}
Arithmetic Expression
switch (
gradeLevel
) {
case 1: System.out.print("Go to the Gymnasium");
break;
Case
Label
case 2: System.out.print("Go to the Science Auditorium");
break;
case 3: System.out.print("Go to Harris Hall Rm A3");
break;
Case
Body
case 4: System.out.print("Go to Bolt Hall Rm 101");
break;
}
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Syntax for the while Statement
while ( <boolean expression> )
<statement>
Boolean Expression
while (
sum
Statement
(loop body)
number <= 100
=
) {
sum + number;
number = number + 1;
}
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Example: Testing Input Data
String inputStr;
int
Priming Read
age;
inputStr = JOptionPane.showInputDialog(null,
"Your Age (between 0 and 130):");
age
= Integer.parseInt(inputStr);
while (age < 0 || age > 130) {
JOptionPane.showMessageDialog(null,
"An invalid age was entered. Please try again.");
inputStr = JOptionPane.showInputDialog(null,
"Your Age (between 0 and 130):");
age = Integer.parseInt(inputStr);
}
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Syntax for the do-while Statement
do
<statement>
while ( <boolean expression> ) ;
do
{
sum += number;
Statement
(loop body)
number++;
}
while (
sum <= 1000000
);
Boolean Expression
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Syntax for the for Statement
for ( <initialization>; <boolean expression>; <increment>
)
<statement>
for (
4) Increment
and back to 2)
2) Boolean
Expression
1)
Initialization
i = 0
;
i < 20
number = scanner.nextInt();
sum += number;
;
i++
) {
3)
(loop body)
}
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Defining a Class
Import Statements
Class Comment
class
{
Class Name
Data Members
Methods
(incl. Constructor)
}
Let us take a look at Bicycle.java, and BicycleRegistration.java
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Creating a Package
• The following steps illustrate the process of creating a
package name myutil that includes the Fraction class.
1. Include the statement
package myutil;
as the first statement of the source file for the Fraction class.
2. The class declaration must include the visibility modifier public as
public class Fraction {
...
}
3. Create a folder named myutil, the same name as the package name. In Java, the
package must have a one-to-one correspondence with the folder.
4. Place the modified Fraction class into the myutil folder and compile it.
5. Modify the CLASSPATH environment variable to include the folder that
contains the myutil folder.
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Arrays of Primitive Data Types
• What is an Array? Why do we need them?
• Array Declaration
<data type> [ ] <variable>
<data type>
<variable>[ ]
//variation 1
//variation 2
• Array Creation
<variable>
= new <data type> [ <size> ]
• Example
Variation 1
Variation 2
double[ ] rainfall;
double rainfall [ ];
rainfall
rainfall
= new double[12];
= new double[12];
An array is like an object!
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Array Processing
double[] rainfall = new double[12];
String[] monthName = new String[12];
monthName[0] = "January";
monthName[1] = "February";
…
double
The same pattern
for the remaining
ten months.
annualAverage, sum = 0.0;
for (int i = 0; i < rainfall.length; i++) {
rainfall[i] = Double.parseDouble(
JOptionPane.showinputDialog(null,
"Rainfall for "
+ monthName[i] ));
sum += rainfall[i];
}
annualAverage = sum / rainfall.length;
The actual month
name instead of a
number.
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Javadoc and Java Style
• General information on javadoc is located at
• http://java.sun.com/j2se/javadoc
• Detailed reference on how to use javadoc on Windows is
located at
• http://java.sun.com/j2se/1.5/docs/tooldocs/windows/javadoc.html
• Java Style Specifics
• http://geosoft.no/development/javastyle.html
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