Java arrays

Arrays
Dr. Kuppusamy .P
Associate Professor / SCOPE

Access Specifiers / modifier in Java
• Defines an access scope of the variable, methods and classes.
• Can change the access level of fields, constructors, methods, and
class by applying the access modifier on it.
1. Public: Accessible from any other class, methods or interface.
2. Private: Accessible within the class or method where it is
defined.
3. Protected: Accessible in the same class or its child class or in all
those classes which are defined in the same package.
4. Default: When none of the access specifiers is specified. Can be
accessed by all classes which are defined in same package only.
Dr. Kuppusamy P

Access Specifiers / modifier in Java
Dr. Kuppusamy P
Access
Modifier
within
class within
package
outside
package by
subclass
only
outside
package
Private Y N N N
Default Y Y N N
Protected Y Y Y N
Public Y Y Y Y

Arrays
• Array is a container object that contains a finite number of values
of a similar data type .
• When an array is created
• The length (size) of an array is fixed
• Array elements are automatically initialized with the default
value of their data type
• Two types
• One dimensional Array
• Multi-dimensional Array
• 2D Array, 3D Array
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One Dimensional Array
• Syntax:
• data-type[] variable = new data-type[array_length]
• Eg. int[] a = new int[6]; //define integer array with size 6
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Create and Initialize Array
• Create and initialize array as below
o int[] x = {10, 20, 30};
o int[] x = new int[] {10, 20, 30};
• Here the length of an array is determined by the number of
values provided between { and }.
• The built-in length property determines the size of any array
• E.g.
o int[] x = new int[10];
oint x_len = x.length;
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Example - Array
public class ArrayEx
{
public static void main(String[] args)
{
int[] marks; // declares an array of integers
marks = new int[5]; // allocates memory for 5integers
marks[0] = 11;
marks[4] = 22;
System.out.println("Element at index 0: " + marks[0]);
}
} Dr. Kuppusamy P

Array bounds and Array Resizing
• Array index (subscripts) begins with 0
• Can't access an array element beyond the defined range.
• Can't resize an array.
• Can use the same reference variable to refer new array.
• int x[] = new int[5];
• x= new int[10];
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Copying Array
• To copy array elements from one array to another array, use
arraycopy static method from System class.
Syntax:
public static void arraycopy(Object s, int sIndex, Object d, int dIndex, int length)
Ex:
int source[] = {1, 2, 3, 4, 5, 6};
int dest[] = new int[10];
System.arraycopy(source, 0, dest, 0, source.length);
Dr. Kuppusamy P

Two-Dimensional Array
• Two-dimensional array is a collection of 1-Dimensional arrays.
• Initializing two-dimensional arrays:
int[][] y = new int[2][4];
• The 1st dimension represent rows or number of one dimension
• The 2nd dimension represent columns or number of elements in the each one
dimensions
Jagged Array:
• Column representation is optional in two dimensional arrays.
int[][] y = new int[3][]
• The curly braces { } may also be used to initialize two dimensional arrays.
Eg: int[][] y = { {1,2,3}, {4,5,6}, {7,8,9} };
int[][] y = new int[3][]
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Two-Dimensional Array
• Array can be initialized with the row dimension and without initializing the
columns, but not vice versa
• int[][] x = new int[3][];
• int[][] x = new int[][3]; //error
• The length of the columns can vary for each row and initialize number of
columns in each row
Ex1:
• int [][] numbers = new int [3][];
• numbers[0] = new int[] {6,9,3,7}; //row1
• numbers[1] = new int [] {5,2} // row2
• numbers[2] = new int [] {8,4,1}; // row3
Dr. Kuppusamy P

Example: 2D-Array
public class TwoD
{
public static void main(String[] args)
{
int [][] x = new int[3][]; // initialize number of rows
x[0] = new int[3]; // define number of columns in each row
x[1] = new int[2];
x[2] = new int[5];
for(int i=0; i < x.length; i++) // print array elements
{
for (int j=0; j < x[i].length; j++)
{
x[i][j] = i;
System.out.print(x[i][j]+ ” “);
}
System.out.println();
}
}
}
Dr. Kuppusamy P

References
Dr. Kuppusamy P
Herbert Schildt, “Java: The Complete Reference”, McGraw-Hill Education, Tenth edition,
2017.

Java arrays

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