JAVA (something like C)

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JAVA (something like C)
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Object Oriented Programming

• Process orientated code acting on data
• Object oriented data controls access to code
• Encapsulation java has a class. The data is
  the state and the methods (code) is the behavior.
  You control the methods and access to the data
• Inheritance where one class acquires the
  properties of another class
• Polymorphism one interface multiple methods

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JAVA editors

• did a search for JAVA editors on the NET and
  obtained...
• JCreator www.jcreator.com
• Download the free one
• editPlus - I have used this one
• http//www.editplus.com/
• shareware - pay after 30 days
• WingSoft
• http//www.wingsoft.com/wingeditor.shtml

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comments

• A single line comment
• int row // keeps track of the row
• multiple line comments
• / this is one line of the comment
• this is the 2nd line
• this is the third line /

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Documentation comments

• acts like multiple line comments
• / this is one line of the comment
• this is the 2nd line
• this is the third line /
• note the initial / The javadoc program
• will collect these blocks of comments as
  documentation for the program
• javadoc filename.java

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special symbols

• indicates a block of code
• ( ) parameters to a method
• indicates an array
• terminates a statement
• , a seperator
• . used to separate package names
• Note table of reserved words on page 39

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Identifier names

• Start with a letter
• Contains
• letters (upper or lower case)
• numbers
• _ (the underscore)
• Can be any length
• No imbedded spaces or special characters
• Do not start an identifier with a number

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Examples/Naming Conventions

• numberOfRows
• num_rows
• row8
• Naming Conventions
• classes start with a capitol letter
• HelloWorld ShoppingCart
• methods identifiers with a small letter
• println() getChar()
• constants are all caps PIE

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System.out.println( )

• System.out.println (.) sends a String to the
  monitor
• System.out.println(Hi Mom)
• The concatenates two variables
• int aVal 17
• System.out.println(a aVal)
• System.out.println(a aV b bV)

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Primitive data types

• JAVA has 8 primitive data type
• Name size -------range-------
• byte 8-bits -128 127
• short 16-bits -32k 32k
• int 32-bits -231 231
• long 64-bits -263 263

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Primitive data types (cont.)

• Name size -------range-------
• float 32-bits - 3.4 X 1038
• double 64-bits - 1.8 X 10308
• char 16-bits 0 65,535
• boolean 1-bit true or false
• (not a 0 or a
  1)

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Examples of primatives

• int x
• int x, y7, zz, rows8
• boolean isRunning false
• double dd
• float f 10.3 (error - defaults to a double)
• float fx 22.4f note the f
• byte b1, b2 44, cx
• short ss5

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The char

• char uses a 16-bit Unicode character set
• The Unicode set allows 65,536 different
  characters. (about half are assigned)
• char ch a
• char ch1, ch2 7, ch3 X
• char delta \u0394 delta symbol
• char copyrt \u00AE copy write symbol
• escape seq. page 32 (EX \t is tab)

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the String class

• String is a class, not a primitive data type
• is a sequence of characters
• not an array of char terminated by a null
• immutable cannot be changed once created
• String ss
• String s1 hi mom
• String s1, suXXX, s3SDE

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Java DOS commands

• Javac A\gtjavac test.java
• compiler
• uses a text file named ????.java
• creates a ????.class file of byte code
• java A\gtjava test
• the interpreter (runs the class code)
• runs an application
• appletviewer A\gtappletviewer test.html
• runs an applet

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Minimum JAVA program

• class Skeleton
• public static void main(String args)
• // end main
• // end class

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arithmetic

• Expression series of variables (methods) that
• evaluate to a single
  variable
• assign (evaluate right, assign to right)
• add x x 7
• - subtract x 8 cx
• multiply pay rate time
• / divide tax too_much / 1.0
• remainder (mod)
• row x 4
• row is the remainder of x / 4
• ans 33 6 ans is 3

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Consider the primitives

• byte 8 bits
• short 16 bits
• int 32 bits
• long 64 bits
• float 32 bits
• double 64 bits
• char 16 bits

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Some examples

• Define and initialize all the primitives
• Add the following to skeleton and compile
• short byte
• byte short
• double float
• float double
• int boolean
• int short byte
• int short float
• double int double
• float short double
• int char chat int

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Conversion and casting

• Automatic
• types are compatible
• destination is larger than the source
• Casting (target type) value
• byte b (byte) someValue
• byte b intExample error
• byte b (byte) intExample OK
• byte b 50
• byte x b/2 Error
• Byte x (byte)(b/2) ok

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Shortcuts in arithmetic

• Shortcuts
• x x x 1
• x-- x x 1
• x7 x x 7
• x3 x x 3
• x/2 y y / 2
• q-5 q q 5

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ternary expression

• expression01 ? expression02 expression03
• Expression01 must evaluate to a boolean
• If expression01 is true,
• expression 02 is evaluated, else
• expression03 is evaluated

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Example of ?

• if (x gt y)
• max x
• else
• max y
• is the same as
• max xgty ? x y

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pre post

• Difference between x and x
• Example
• int x 5
• System.out.println(x x)
• int x 5
• System.out.println(x x)

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Operator precedence

• Do work within ( )
• Then, left to right.
• --
• /
• -
• Whats the answer to the following..
• n 1 - 2 3 - 4 5

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if statement

• if(expression) // expression is evaluated
• block of code // execute if true
• else
• block of code // execute if false
• Note a block of code can contain a nested
  if statement

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examples

• if (x gt 6)
• System.out.println(x is bigger)
• else
• System.out.println(x is less than 6)
• if (xgt8)
• else
• System.out.println(x is less than 8)

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logical operators

• evaluate both, both must be true
• evaluate both, either must be true
• both must be true. If 1st is false, do not
  evaluate the 2nd
• one must be true. If 1st is true, do not
  evaluate the 2nd
• tilda - not
• Shift and bit-wise operators you are on your
  own (page 80)

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and

• if ((agtb) (clt7))
• System.out.println(both true)
• else
• System.out.println(one not true)
• if ((agtb) (clt7))
• System.out.println(both true)
• else
• System.out.println(one not true)

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and

• if ((agtb) (clt7))
• System.out.println(at least one true)
• else
• System.out.println(both false)
• if ((agtb) (clt7))
• System.out.println(at least one true)
• else
• System.out.println(both false)

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• if ((agtb) (a))
• System.out.println((true)a a)
• else
• System.out.println((false)a a)
• if (agtb)
• if (c!7)
• System.out.println(123456)
• is the same as
• If((agtb) (c!7))
• System.out.println(123456)

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Relational operators

• equal to
• ! not equal
• gt greater than
• lt less than
• gt greater than or equal to
• lt less than or equal to

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The loops

• For a loop you need 3 things
• a counter of some kind
• a comparison statement - a test
• increment the counter some time
• the loops are

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for loop

• for (int i 6 ilt5 i)
• System.out.println(counter is i)
• the for statement contains the counter,
  increment, and test all together

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example

• For (int k0 klt3 k)
• System.out.println(k)
• for (int d5 dlt3 d)
• System.out.println(k)
• for (int d3, int e7 dlte d, e--)
• System.out.println(d and e e)

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for loop using a comma

• for (a 1, b4 altb a, b--)
• System.out.println(a a)
• System.out.println(b b)
• Gives a 1
• b 4
• a 2
• b 3

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for loop some variations

• boolean done false
• for (a 1 !done a)
• done true
• boolean done false
• for ( !done )
• done true

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while loop

• int x0 //
  counter
• while (xlt5) // test
• System.out.println(counter x)
• x //
  increment

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Example 1

• int x4 //
  counter
• while (xlt5) // test
• System.out.println(counter x)
• x //
  increment

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Example 2

• int x4 //
  counter
• while (xlt5) // test
• System.out.println(counter x)

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Example 3

• int x14 //
  counter
• while (xlt5) // test
• System.out.println(counter x)
• x //
  increment

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do/while loop

• int c3 //
  counter
• do
• System.out.println(counter c)
• c //
  increment
• while (clt5) // test
• whats special about a do/while loop??

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Example 1

• int c3 //
  counter
• do
• System.out.println(counter c)
• while (clt5) // test

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Example 2

• int c13 //
  counter
• do
• System.out.println(counter c)
• c //
  increment
• while (clt5) // test

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Switch statement

• switch(expression)
• case value01 statement
• break
• case value02 statement
• break
• default statement
• The expression is evaluated. Jump to the
  corresponding case statement with value

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• expression must be a byte, short, int, or char
• When you jump to the proper case value, you
  execute code until the end of the switch
  statement or a break statement is executed
• No matches jump to default
• No default out of switch

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• Switch(month)
• case 1 days31
• break
• case 2 days28
• break
• case 3 days31
• break
• case 4 days30
• break
• case 12 days31
• break
• default days0

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• switch(month)
• case 9
• case 4
• case 6
• case 11 days30
• break
• case 2 days28
• break
• default days31

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More use of break

• hitting a break will terminate a loop
• for(int x0 xlt100 x)
• if (x5) break
• System.out.println(X x)
• X0
• X1
• X2
• X3
• X4

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• Using break in nested loops
• for(int x1 xlt4 x)
• System.out.println(X x)
• for (int y0 ylt30 y)
• if (yx) break
• System.out.println (Y y)

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break with the while loop

• while (xlt100
• if (x5) break
• System.out.println(X x)
• x
• X0
• X1
• X2
• X3
• X4

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break with a label

• outer for(i1 ilt100 i)
• for (j4 jlt50 j)
• .
• if((ji)0)
• break outer
• ..
• // end j for loop
• // end i for loop
  

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continue statement

• for (int x0 xlt8 x)
• System.out.print(x )
• if(x2) continue
• System.out.println( )
• 0 1
• 2 3
• 4 5
• 6 7

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break / continue / go to

• break and continue may specify a label
• a label is a JAVA identifier that indicates a
  block of code
• aLabel
• stuff
• It is close to a GoTo. Dont use it