1. ARRAYS
in
JAVA

2. TOPICS TO COVER:--
 Array declaration and use.
 One-Dimensional Arrays.
 Passing arrays and array elements as parameters
 Arrays of objects
 Searching an array
 Sorting elements in an array

3. ARRAYS
 An array is group of like-typed variables that are referred to
by a common name.
The entire array Each value has a numeric index
has a single name
0 1 2 3 4 5 6
scores 50.5 12.8 4.05 78 66 100 125
50 12 45 7.8 0.66 1.00 12.5
An array of size N is indexed from zero to N-1
INTEGER
FLOAT
 An array can be of any type.
 Specific element in an array is accessed by its index.
 Can have more than one dimension

4. 2D Array Elements
Row
 Requires two indices
 Which cell is
CHART [3][2]?
Column
[0] [1] [2] [3] [4] [5]
[0] 0 97 90 268 262 130
[1] 97 0 74 337 144 128
[2] 90 74 0 354 174 201
[3] 268 337 354 0 475 269
[4] 262 144 174 475 0 238
[5] 130 128 201 269 238 0
CHART

5. Arrays
 A particular value in an array is referenced using the array
name followed by the index in brackets
 For example, the expression
scores[2]
refers to the value 45 (the 3rd value in the array)
0 1 2 3 4 5 6
50 12 45 78 66 100 125
5

6. DECLARAING ARRAYS
 The general form of 1-d array declaration is:-
type var_name[ ]; 1. Even though an array variable
“scores” is declared, but there
int, float, char array name is no array actually existing.
2. “score” is set to NULL, i.e.
E.g.:--- int scores [ ]; an array with NO VALUE.
scores
int[] scores = new int[10];
NULL
To link with actual, physical array of integers….

7. Declaring Arrays
 Some examples of array declarations:
double[] prices = new double[500];
boolean[] flags;
flags = new boolean[20];
char[] codes = new char[1750];
8

8. ARRAY INITIALIZATION
 Giving values into the array created is known as
INITIALIZATION.
 The values are delimited by braces and separated by commas
 Examples:
int[ ] units = {147, 323, 89, 933, 540, 269, 97, 114, 298, 476};
char[ ] letterGrades = {'A', 'B', 'C', 'D', ’F'};
 Note that when an initializer list is used:
 the new operator is not used
 no size value is specified
 The size of the array is determined by the number of items in the
initializer list. An initializer list can only be used only in the array
declaration

9. ACCESSING ARRAY
 A specific element in an array can be accessed by
specifying its index within square brackets.
 All array indexes start at ZERO.
Example:- System.out.println(units[4]);
mean = (units[0] + units[1])/2;
0 1 2 3 4 5 6 7 8 9
int[ ] units = {147, 323, 89, 933, 540, 269, 97, 114, 298, 476};

10. PROCESSING ARRAY ELEMENTS
 Often a for( ) loop is used to process each of the elements
of the array in turn.
 The loop control variable, i, is used as the index to access array
components
EXAMPLE:- int i;
score [0]
for(i=0;i<=2;i++)
{
System.out.println(+score[i]);
} 0 1 2 3 4 5 6
score
50 12 45 78 66 100 125

11. int i; score [1]
for(i=1;i<=2;i++)
{
System.out.println(+score[i]);
}
0 1 2 3 4 5 6
score
50 12 45 78 66 100 125

13. Bounds Checking
 Once an array is created, it has a fixed size
 An index used in an array reference must specify a valid
element
 That is, the index value must be in bounds (0 to N-1)
 The Java interpreter throws an
ArrayIndexOutOfBoundsException if an array index
is out of bounds
 This is called automatic bounds checking
14

14. Bounds Checking
 For example, if the array score can hold 100 values, it
can be indexed using only the numbers 0 to 99
 If i has the value 100, then the following reference will
cause an exception to be thrown:
System.out.println (score[i]);
 It’s common to introduce off-by-one errors when using
arrays problem
for (int i=0; i <= 100; i++)
score[i] = i*50;
15

15. ARRAY OF OBJECTS
 Create a class student containing data members Name,
Roll_no, and Marks.WAP in JAVA to accept details of 5
students. Print names of all those students who scored
greater than 85 marks
student
Chris,101,85
student[0]
student[1] Brad, 102,75.8
student[2]
student[3] Andrew, 103,75.9

16. Recursion
• Recursion is the process of defining something
in terms of itself.
• It allows a method to call itself.
compute()
In general, to solve a problem using recursion, you
break it into sub problems.
AREAS WHERE RECURSION CAN BE USED…………….
 FACTORIAL OF A NUMBER.
FIBONACCI SERIES.
GCD OF TWO NUMBERS.
TOWER OF HANOI.
QUICK SORT.
MERGE SORT.

17. Recursion Example
cal (5)
return 5 +cal (4)
return 4 +cal (3)
6
return 3 +cal (2)
3
return 2 +cal (1)
TO WHOM??????
return 1 1
5 cal(5) CALLING FUNCTION

18. Iteration vs. Recursion
ITERATION RECURSION
• Certain set of instructions • Certain set of
are repeated without instructions are repeated
calling function. calling function.
• Uses for, while, do-while • Uses if, if-else or switch.
loops.
• More efficient because of • Less efficient.
better execution speed.

19. COMPARSION contd….
• Memory utilization is • Memory utilization is
less. more.
• Complex to implement.
• Simple to implement.
• More lines of code. • Brings compactness in
the program.
• Terminates when loop
• Terminates when base
condition fails.
case is satisfied.

20. GCD USING RECURSION
ALGORITHM:-
int GCD(int a, int b)
{
if(b>a)
return (GCD(b, a));
if(b==0)
return (a);
else
return (GCD(b,(a%b));
}

21. FIBONACCI SERIES USING RECURSION
int fibo(int f1,int f2,int count)
{
if(count==0) then
return 0;
else
f3=f1+f2;
f1=f2;
f2=f3;
System.out.print(" "+f3);
count--;
return fibo(f1,f2,count);
}

22. TWO- DIMENSIONAL ARRAY
 DECLARATION:-
Follow the same steps as that of simple arrays.
Example:-
int [ ][ ]; int chart[ ][ ] = new int [3][2];
chart = new int [3][2];
 INITIALIZATION:-
15 16
int chart[3][2] = { 15,16,17,18,19,20}; 17 18
19 20
int chart[ ][ ] = { {15,16,17},{18,19,20} };
15 16 17
18 19 20

23. PROGRAM FOR PRACTISE
 The daily maximum temperature is recorded in 5 cities during 3
days. Write a program to read the table elements into 2-d array
“temperature” and find the city and day corresponding to “ Highest
Temperature” and “Lowest Temperature” .
 Write a program to create an array of objects of a class student. The
class should have field members id, total marks and marks in 3
subjects viz. Physics, Chemistry & Maths. Accept information of 3
students and display them in tabular form in descending order of the
total marks obtained by the student.