Transcript A Guide to Programming in Java

Chapter 4
Assignment Statement
An assignment statement gives a value to a variable.
Assignment can take several forms:
x = 5;
a literal (5) is assigned to x
x = y + 2;
the value of an expression (y + 2) is
assigned to x
x = z;
the value of another variable (z) is
assigned to x
Slide 1
Chapter 4
Variable Assignment
A variable can store only one value at any time.
int x;
x = 5;
x = 10;
Slide 2
x
10
5
Chapter 4
Primitive Data Types
Type
int
double
char
boolean
Slide 3
Storage Required
4 bytes
8 bytes
2 bytes
1 bit
Classic Asteroids Game
from Atari
Slide 4
A variable declared with a class is called an object. For
example, the object a47 is type Asteroid:
Asteroid a47 = new Asteroid();
a47
a47.setLocation(x,y)
a47.destroy()
Slide 5
Chapter 4
Java Packages
 Numerous packages are included with JRE
(Java Runtime Environment)
 Packages contain classes
 Packages can be added to an application with an
import statement. For example, the statement
import java.util.Scanner;
makes the Scanner class and its methods
accessible to the application.
Slide 6
Chapter 4
The Scanner Class
 Part of the java.util package
import java.util.*;
 A Scanner object processes text and numbers from
the input stream
 Methods include:
next()
nextLine()
nextInt()
nextDouble()
nextBoolean()
close()
Slide 7
Chapter 4
Integer Division
Integer division (/) is performed when both operands
are integers. Only the integer portion of the quotient is
returned:
Source Code
int answer;
answer = 20 / 7;
System.out.print(answer);
Output
2
Slide 8
Chapter 4
Real Division
Real division (/) is performed when one or both
operands are type double. The entire quotient,
including the decimal portion is returned:
double result;
result = 20.0/7.0;
Slide 9
//result is 2.857
Chapter 4
Modulus Division
Modulus division (%) returns the remainder of a
division operation:
Source Code
int answer;
answer = 20 % 7;
System.out.print(answer);
Output
6
Slide 10
Chapter 4
Operator Precedence
Operators in Java have the following precedence:
1. multiplication and division
2. addition and subtraction
Operators of the same precedence are evaluated in
order from left to right. For example, multiplication is
performed first, then division, and finally addition:
5 + 6 * 4 / 2 = 17
Slide 11
Chapter 4
Changing the Order of Operations
The order in which operators are evaluated can be
changed by using parentheses. For example, addition
is performed first, then multiplication, and finally
division:
(5 + 6) * 4 / 2 = 22
Slide 12
Chapter 4
Type Casting
Assigning an integer value into a floating-point
variable works just fine. For example:
double bankAccountBalance = 1000;
However assigning a floating-point value into an
integer variable is like trying to fit a large object in
a small box.
By default, Java treats it as an illegal operation. For
example, this causes an error:
int temperature = 22.8;
Slide 13
Chapter 4
Type Casting
Type Casting converts a number of one type to a
number of a different, but compatible type. Type
casting is used to:
1. make the operand types in an expression match.
For example, wholeNum = (int)y * 2
2. truncate the decimal portion of a double. For
example, wholeNum = (int)z
3. change the way in which a division (/) operation
will be performed. For example,
realDivision = (double)a / (double)b
Slide 14
Chapter 4
Assignment Operators
Operator
+=
-=
*=
/=
%=
Slide 15
Operation
addition and then assignment
subtraction and then assignment
multiplication and then assignment
division and then assignment
modulus division and then assignment
Chapter 4
Named Constants
 A named memory location that cannot be changed from
its initial value.
 The keyword final is used in a constant declaration.
 Constant identifiers are typically all uppercase with an
underscore (_) separating words within the identifier
name.
Slide 16
Chapter 4
Java Keywords
abstract
boolean
break
byte
case
catch
char
class
const
continue
default
do
Slide 17
double
else
extends
final
finally
float
for
goto
if
implements
import
instanceof
int
interface
long
native
new
package
private
protected
public
return
short
static
strictfp
super
switch
synchronized
this
throw
throws
transient
try
void
volatile
while
Chapter 4
Programming Errors
 Syntax errors violate the rules of Java.
 Logic errors, also called semantic errors, occur in
statements that are syntactically correct, but produce
undesired or unexpected results.
 Run-time errors, also called exceptions, halt program
execution at the statement that cannot be executed. One
type of exception is called InputMismatchException.
Slide 18
Chapter 4
Flowchart Symbols
process
Slide 19
Chapter 4
The BirthdayGame Flowchart
Slide 20