Java Language Basics

1
Java Language Basics

• Variables
• Operators
• Expressions, Statements, and Blocks
• Control Flow Statements

2
Variables

• An object stores its state in variables.
• Definition  A variable is an item of data named
  by an identifier.
• Name
• Type
• Scope

3
Data Types

• Examples int number double bigNumber
• Primitive
• A variable of primitive type contains a single
  value of the appropriate size and format for its
  type a number, a character, or a boolean value
• Reference
• The value of a reference type variable, in
  contrast to that of a primitive type, is a
  reference to (an address of) the value or set of
  values represented by the variable. Arrays,
  classes, and interfaces are reference types.

4
Primitive Data Types

• Integer Types
• byte, short, int, long.
• Real Types
• float, double.
• Other Types
• char, boolean.

5
Arrays

• An array is a structure that holds multiple
  values of the same type. The length of an array
  is established when the array is created (at
  runtime). After creation, an array is a
  fixed-length structure.

6
Arrays

• int anArray // declare an array of integers
• anArray new int10 // create an array of
  integers
• To get the size of an array you can use
  arrayname.length
• Shortcut for creating and initializing an
  arrayboolean answers true, false, true,
  true, false

7
Variable Scope

• A variable's scope is the region of a program
  within which the variable can be referred to by
  its simple name.
• Secondarily, scope also determines when the
  system creates and destroys memory for the
  variable.
• The location of the variable declaration within
  your program establishes its scope and places it
  into one of these four categories
• Member variable,
• Local variable,
• Method parameter,
• Exception-handler parameter,

8
Variable Scope
9

• Exercise
• http//cse.yeditepe.edu.tr/taytekin/cse252/lab/Ma
  xVariablesDemo.java

10
Operators

• Arithmetic Operators
• Relational and Conditional Operators
• Shift and Logical Operators
• Assignment Operators
• Other Operators

11
Arithmetic Operators

• (op1 op2)
• - (op1 - op2)
• (op1 op2)
• / (op1 / op2)
• (op1 op2)

12
Arithmetic Operators

• Data Type of Result Data Type of Operands
• long Neither operand is a float or a
  double (integer arithmetic) at least one
  operand is a long.
• int Neither operand is a float or a
  double (integer arithmetic) neither
  operand is a long.
• double At least one operand is a double.
• float At least one operand is a float
  neither operand is a double.

13
Relational and Conditional Operators

• Op. Use Returns true if
• gt op1 gt op2 op1 is greater than op2
• gt op1 gt op2 op1 is greater than or equal to
  op2
• lt op1 lt op2 op1 is less than op2
• lt op1 lt op2 op1 is less than or equal to op2
• op1 op2 op1 and op2 are equal
• ! op1 ! op2 op1 and op2 are not equal

14
Conditional Operators

• Op. Use Returns true if
• op1 op2 op1 and op2 are both true,
  conditionally evaluates op2
• op1 op2 either op1 or op2 is true,
  conditionally evaluates op2
• ! ! op op is false
• op1 op2 op1 and op2 are both true, always
  evaluates op1 and op2
• op1 op2 either op1 or op2 is true, always
  evaluates op1 and op2
• op1 op2 if op1 and op2 are different--that
  is if one or the other of the operands is true
  but not both

15
Assignment Operators

• Op. Use Equivalent to
• op1 op2
• op1 op2 op1 op1 op2
• - op1 - op2 op1 op1 - op2
• op1 op2 op1 op1 op2
• / op1 / op2 op1 op1 / op2
• op1 op2 op1 op1 op2

16

• Operator Description
• ? Shortcut if-else statement
• Used to declare arrays, create arrays,
  and access array elements
• . Used to form qualified names
• ( params ) Delimits a comma-separated list of
  parameters
• ( type ) Casts (converts) a value to the
  specified type
• New Creates a new object or a new array
• Instanceof Determines whether its first operand
  is an instance of its second operand

17
Exercise

• Write a program that calculates the number of US
  dollars equivalent to a given number of French
  francs. Assume an exchange rate of 6.85062 francs
  per dollar. If you want to control the format of
  the numbers your program displays, you can use
  the DecimalFormat class.

18
Control Flow Statements

• Statement Type Keyword
• looping while, do-while , for
• decision making if-else, switch-case
• exception handling try-catch-finally, throw
• branching break, continue, label, return

19
The while and do-while Statements

• while (expression)
• statement
• do
• statement(s)
• while (expression)

20
The for statement

• for (initialization termination increment)
  statement
• Example
• for (int i 0 i lt arrayOfInts.length i)
  System.out.print(arrayOfIntsi " ")

21
The if/else Statements

• if (testscore gt 90)
• grade 'A'
• else if (testscore gt 80)
• grade 'B'
• else if (testscore gt 70)
• grade 'C'
• else if (testscore gt 60)
• grade 'D'
• else
• grade 'F'

22
The switch Statement

• int month 8
• switch (month)
• case 1 System.out.println("January") break
• case 2 System.out.println("February") break
• case 3 System.out.println("March") break
• case 4 System.out.println("April") break
• case 5 System.out.println("May") break
• case 6 System.out.println("June") break
• case 7 System.out.println("July") break
• case 8 System.out.println("August") break
• case 9 System.out.println("September") break
• case 10 System.out.println("October") break
• case 11 System.out.println("November") break
• case 12 System.out.println("December") break

23
Exception Handling Statements

• try
• statement(s)
• catch (exceptiontype name)
• statement(s)
• finally
• statement(s)

24
Exception Example

• try
• PrintWriter out null
• out new PrintWriter(new FileWriter("OutFile.txt
  "))
• catch (FileNotFoundException e)
• System.err.println("IOException "
  e.getMessage())
• catch (IOException e)
• System.err.println("IOException "
  e.getMessage())

25
Branching Statements

• An unlabeled break statemets terminates the
  execution of a for, switch, while, or do-while
  statements.
• You use the continue statement to skip the
  current iteration of a for, while , or do-while
  loop.
• You use return to exit from the current method.

26
Exercises

• Write a program that calculates the number of
  YTLs equivalent to a given amount of TLs. For
  example 1200000 TL is equal to 1.2 YTL. If you
  want to control the format of the numbers your
  program displays, you can use the DecimalFormat
  class. Do not take any inputs from the user. The
  amount of TL is present in an instance variable.
• Write a program which implements the bubble sort
  algorithm. An array of integers should be given
  to the program as an instance variable. Your code
  should print the sorted result.