Lecture 3 Program Elements

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Lecture 3Program Elements
Instructors Fu-Chiung Cheng (???) Associate
Professor Computer Science Engineering Tatung
Institute of Technology
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Outline

• Data types
• Variable declaration and use
• Decisions and loops
• Input and output

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Primitive Data Types

• A data type define values and the operators
• Each value stored in memory is associated with a
  
• particular data type
• primitive data types predefined data types in
  Java
• Ex A integers byte, short, int, long.
• B float, double.
• C boolean (true or false) (on or off)
• D char (unicode 16 bits for
  international languages)

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Storage in Programming Languages

• Registers
• Stack (handles primitives in Java)
• Heap (all class objects in Java)
• Static storage
• Constant storage
• Non-RAM storage (persistent)

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Primitive Data Types

• Integers

Type byte short int long
Storage 8 bits 16 bits 32 bits 64 bits
Min Value -128 -32,768 -2,147,483,648 lt -9 x 1018
Max Value 127 32,767 2,147,483,647 gt 9 x 1018
Note that Built-in types (primitives) are not
object handles handles call by reference
primitives call by value
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Primitive Data Types

• Floating point

Approximate Min Value -3.4 x 1038 -1.7 x 10308
Approximate Max Value 3.4 x 1038 1.7 x 10308
Type float double
Storage 32 bits 64 bits
S
Exponent
Mantisa
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Primitive Data Types

• char Unicode character set
• A character set is an ordered list of characters
• The Unicode character set uses sixteen bits per
  character,
• allowing for 65,536 unique characters
• International character set.

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Primitive Data Types

• boolean a true or false condition (two states
  on or off)
• The reserved words true and false are the
• only valid values for a boolean type

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Primitive Data Types

• Same operations as C/C
• Size of each data type is machine independent

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Wrappers for primitive Data Types

• For each primitive data type there is a
  corresponding
• wrapper class.
• Wrapper classes are useful in situations where
  you need
• an object instead of a primitive type
• They also contain some useful methods

Primitive Type int double char boolean
Wrapper Class Integer Double Character Boolean
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Variables

• A variable is an identifier that represents a
  location in
• memory that holds a particular type of data
• Variables must be declared before they can be
  used
• Syntax of a variable declaration
• data-type variable-name
• For example
• int total // 4-byte int in stack
• int total, count, sum
• int total 0, count 20
• float unitPrice 57.25

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Scope of Variables

• Block statements
• group of statements delimited by braces
• // begin of scope 1
• int x1
• System.out.println("x"x)
• // begin of scope 2
• // int x3 // can not redine x
• int y2
• System.out.println("x"x)
• System.out.println(yy)

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Assignment Statements

• An assignment statement takes the following
  form
• variable-name expression
• The expression is evaluated and the result is
  stored in
• the variable, overwriting the value currently
  stored
• in the variable
• The expression can be a single value or a more
• complicated calculation

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Constants

• A constant is similar to a variable except that
  they keep
• the same value throughout their existence
• They are specified using the reserved word final
  
• in the declaration. For example
• final double PI 3.14159
• final int STUDENTS_COUNT 25
• All final are static.
• final static double PI 3.14159
• Better than literal values because
• A. make code more readable by giving meaning to
  a value
• B. use less memory, easy to modification (one
  place)

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Input and Output

• Java I/O is complicated.
• 1. Different kind of IO
• Files, console, block of memory, network
• 2. Different kinds of operations
• Sequential, random-access, binary,
• character, integer, by lines, be words, ...
• Java provides a lot of classes to support IO.

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Input and Output

• Java I/O is based on input streams and output
  streams
• 1. All classes inherit from IS have read
  methods.
• 2. All classes inherit from OS have write
  methods.
• There are three predefined standard streams
• print and println methods write to
• standard output

Stream System.in System.out System.err
Purpose reading input writing output writing
errors
Default Device keyboard monitor monitor
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Input and Output

• Escape sequences a special sequence of
  characters
• preceded by a backslash (\)

Escape Sequence \t \n \" \' \\
Meaning tab new line double quote single
quote backslash
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Types of Output Stream
Writes to
ByteArrayOutputStrem
Block of Memory
FileOutputStrem
File
PipeOutputStrem
Pipe(to another thread)
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Types of Input Stream
Reads from
ByteArrayInputStrem
Block of Memory
FileInputStrem
File
PipeInputStrem
Pipe(to another thread)
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Input From Keyboard

• The Java API allows you to create many kinds of
  streams
• to perform various kinds of I/O
• To read character strings, we will convert the
• System.in stream to another kind of stream
  using
• BufferedReader stdin new BufferedReader
• (new InputStreamReader
  (System.in))
• This declaration creates a new stream called
  stdin

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Echo.java
import java.io. class Echo public
static void main (String args) throws
IOException BufferedReader stdin new
BufferedReader (new
InputStreamReader(System.in)) String
message System.out.println ("Enter a line
of text") message stdin.readLine()
System.out.println ("You entered \"" message
"\"") // method main // class Echo

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Open File
public class Scanner protected static
DataInputStream inputStream Scanner(String
fileName) throws IOException inputStream
new DataInputStream (new FileInputStream
(fileName))
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Buffers

• As you type, the characters are stored in an
  input buffer
• When you press enter, the program begins
  processing
• the data
• Output information is temporarily stored in an
• output buffer
• The output buffer can be explicitly flushed
• (sent to the screen) using the flush method
• See Python.java

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Numeric Input

• Converting a string into the integer value
• value Integer.parseInt(my_string)
• A value can be read and converted in one line
• num Integer.parseInt(stdin.readLine())
• C scanf(d\n, num)

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Addition2.java
import java.io. class Addition2 public
static void main (String args) throws
IOException BufferedReader stdin new
BufferedReader (new InputStreamReader(S
ystem.in)) int num1, num2
System.out.println ("Enter a number ")
num1 Integer.parseInt (stdin.readLine())
System.out.println ("Enter another number")
num2 Integer.parseInt (stdin.readLine())
System.out.println ("The sum is "
(num1num2)) // method main // class
Addition2
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Controlling Program Flow

• Essentially same as C/C
• if statement
• if (condition)
• statement
• Relational operators

Operator ! lt lt gt lt
Meaning equal to not equal to less than less
than or equal to greater than greater than or
equal to
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Controlling Program Flow

• if-else statement
• if (condition)
• statement1
• else
• statement2
• while statement
• while (condition)
• statement
• Note Avoid infinite loop (logic error)

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Controlling Program Flow

• if-else statement
• if (condition)
• statement1
• else
• statement2
• while statement for statemetn
• while (condition) for (e1e2e3)
• statement statement
• Note Avoid infinite loop (logic error)

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import java.io. class Right_Triangle // bad
bad bad RightTriangle public static void main
(String args) throws IOException
BufferedReader stdin new BufferedReader
(new InputStreamReader(System.in)) int
hypotenuse_sq // bad hypotenuseSquare
System.out.println ("Enter side 1") int
side1 Integer.parseInt (stdin.readLine())
System.out.println ("Enter side 2") int
side2 Integer.parseInt (stdin.readLine())
System.out.println ("Enter the hypotenuse")
int side3 Integer.parseInt
(stdin.readLine()) hypotenuse_sq (side1
side1) (side2 side2) if
((side3side3) hypotenuse_sq)
System.out.println ("It is a right triangle.")
else System.out.println ("It is not
a right triangle.") // method main //
class Right_Triangle
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Conclusion

• primitive data types predefined data types in
  Java
• Size of each primitive data type is machine
  independent
• Beware of scope(variables can not be redefined
  in blocks)
• Java I/O is complicated.
• IO is based input streams and output streams

?? Lecture 3 ?????!