Revision From Last Lecture

1
Revision From Last Lecture

• String functions
• API referencing from sun java doc
• Any questions?

2
Arrays

• Why use arrays?
• To group similar typed and related data for ease
  of your program usability
• Extremely easy to use

3
Arrays (Contd)

• So, an array
• Is a sequence of related values
• Has a user-specified fixed length
• Is homogenous
• Provides fast random access

4
Arrays (Contd)

• We have to write a program which involves
  manipulation of large set of variables , say a
  list of movies
• Are they related? (Although not a necessity)
• Are they homogenous (list of strings?)

5
Arrays (Contd)
6
Arrays (Contd)
String moviesnew String10 movies0 The
Godfather movies1 The Shawshank
Redemption movies2 ... movies9
Star Wars Empire Strikes Back System.out.prin
tln(movies 1 )
7
Arrays (Contd)

• // Example 2
• public static void main (String args)
• int A 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
• // alternate way of declaring and defining an
  array.
• // We can also use this method in our previous
  example. How?
• for ( int i 0 i lt A.length i )
• System.out.println( Ai )
• Now we can also use length attribute in our
  previous example as well

8
Arrays and Functions Combined

• // Example 3
• public static int fibonacci( int n )
• if ( n lt 1 ) return 1
• int A new int n 1
• A 0 A 1 1
• for ( int i 2 i lt n i )
• A i A i 1 A i 2
• return A n
• How does this function work?

9
Arrays Review of Last Lecture

• We focused on
• Array Declarations
• Inserting values in arrays
• Getting values out of arrays

10
Arrays as Parameters and Return Values in Methods

• Array parameters and return values
• Are passed by reference i.e. are not copied
• They can be modified inside functions

11
Example 1

• public static void main(String args)
• int numbers 1,2,3,4,5
• printdouble(numbers)
• for (int i 0 i lt numbers.length i)
• System.out.println( numbersi )
• public static void printdouble(int nums)
• for ( int j 0 j lt nums.length j )
• nums j 2
• System.out.println( nums j )

12
Example 2

• public static int findMean( int A )
• int sum 0
• for ( int i 0 i lt A.length i )
• sum A i
• return sum / A.length

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Example 3

• public static void printPrimes( int n )
• boolean isPrime new boolean n 1
• for ( int i 1 i lt n i ) isPrimei
  true
• for ( int d 2 d lt n d )
• for ( int dd 2d dd lt n dd d )
• isPrime dd false
• for ( int i 1 i lt n i )
• if ( isPrime i ) System.out.println( i )

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Example 4

• public static void main(String args)
• int sum 0
• for ( int i 0 i lt args.length i )
• sum Integer.parseInt(argsi)
• System.out.println( The sum sum )

15
Example 5

• Refer to the CS7 site

16
2-Dimensional Arrays

• A 2-d array
• Is often known as Matrix
• Defined with int M new introwscolumns
• Often accessed with pair of nested FOR loops

17
2-D Array An Illustration
M
M00 M01 M02
M0col-1
M10 M11 M12
M1col-1
M20 M21 M22
M2col-1
Mrow-10 Mrow-11
Mrow-1col-1
18
Example

• public static void main( String args )
• int M new int 6 3
• for (int row 0 row lt M.length row)
• for (int col0colltM0.lengthcol)
• Mrowcol row col
• for (int row0 row lt M.length row)
• for (int col0colltMrow.lengthcol)
• System.out.print(Mrowcol )
• System.out.println()

19
Illustration of the last example
M63
M00 M01 M02
M10 M11 M12
M20 M21 M22
M30 M31 M32
M40 M41 M42
M50 M51 M52
Matrix