Lecture 6
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The document discusses Java arrays. Some key points covered include: - Arrays are objects that store a group of data of the same type in contiguous memory locations. They can store primitive types or objects. - Arrays are declared using square brackets and must specify a dimension. They are zero-based and accessed via indexes. - Arrays are initialized using the new operator and default initialized. Their length can be accessed via the length field. - Multidimensional arrays are arrays of arrays, with irregular sizes allowed. Methods like arraycopy can copy arrays.
![Core Java
Debasish Pratihari
Array :
In Java arrays are objects that represent a
group of contiguous memory locations of the
same type and referred to by the same name.
The element type for an array can be any
primitive data type or object.
All Java arrays are technically one-dimensional.
Two-dimensional arrays are arrays of arrays.
Declaring an array does not create an array
object or allocate space in memory; it creates a
variable with a reference to an array
Array variable declarations must indicate a
dimension by using []
All arrays are zero-based
Arrays must be indexed by int values or byte,
short or char values (as these can be promoted
to int)
Using a long index value to access an array
causes a compile error
Attempting to access an array with an index less
than 0 or greater than the length of the array
causes an ArrayIndexOutOfBoundsException
to be thrown at runtime
Since arrays are Objects they can be initialized
using the new operator
When created, arrays are automatically
initialized with the default value of their type
Array references declared as members are
initialized to null BUT array references declared
in methods are not initialized
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![Core Java
Debasish Pratihari
Examples of valid array declarations :
String[]s;
String s[];
String[][]s;
String s[][];
String[] s[];
Initializing Array :
String[ ] s = new String[100]; // default values: null
boolean[] b = new boolean[4]; // default values: false
int i[ ]= new int[5];
int[][] i = new int[10][10];
// default values: 0
String[] oneDimArray = { "abc","def","xyz" };
int[] array = null;
int[][] twoDimArray = { {1,2,3}, {4,5,6}, {7,8,9} };
int[] a = { 1, primes[2], c, (int)Math.pow(2,2) };
int[] arr = new int[] {1,2,3};
int[][] myArray = new int[5][];
int arrSize = 100;
String[] myArray = new String[arrSize];
Illegal Initialization of Array :
String[5] s;
int[] array = new int[];
int[][] myArray = new int[][5];
String[] s;
s = { "Lakshya", "debasish", "java"};
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![Core Java
Debasish Pratihari
Finding length of an Array :
Arrays have a length data field (read only),
specifying the number of elements in the array.
The length data field can be accessed through
the dot operator.
The bounds of an array are integers between 0
and length – 1
Example
for ( int k=0; k < a.length ; k++ )
System.out.println( a[ k ] );
Multidimensional Arrays:
Multidimensional arrays are implemented as
arrays of arrays. Multidimensional arrays are
declared by appending the appropriate number
of bracket pairs after the array name.
The number of elements in each direction need
not be specified in the declaration.
The number of elements in each direction need
not be equal.
Example of irregular Array :
int[][] irregular = { { 1 },
{ 2, 3 },
{ 4, 5, 6, 7 },
{0}
};
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![Core Java
Debasish Pratihari
An Example -Triangle Array :
Output
int[][] triangle = new int[10][];
for ( int j = 0; j<triangle.length ; j++ )
triangle[ j ] = new int[ j + 1 ];
for ( int i = 0 ; i < triangle.length ; i++ )
{
for ( int j = 0 ; j < triangle[i].length ; j++ )
System.out.print( triangle[i][j] + " " );
System.out.println();
}
0
00
000
0000
00000
000000
0000000
00000000
000000000
0000000000
Coping Array :
25%
Arrays can be copied using the Java System
method arraycopy():
Signature:public static native void
arraycopy(Object src, int src_position, Object
dst, int dst_position, int length)
Parameters:
src - the source array.
src_position - start position (first cell to copy) in the
source array.
dst - the destination array.
dst_position - start position in the destination array.
length - the number of array elements to be copied.
By default, all Java arrays support the clone
method.
Things to Remember :
An array is a container object that holds a
fixed number of values of a single type.
The length of an array is established when
the array is created. After creation, its
length is fixed.
Each item in an array is called an element
each element is accessed by its numerical
index.
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Lecture 6
- 1. Core Java Debasish Pratihari Array : In Java arrays are objects that represent a group of contiguous memory locations of the same type and referred to by the same name. The element type for an array can be any primitive data type or object. All Java arrays are technically one-dimensional. Two-dimensional arrays are arrays of arrays. Declaring an array does not create an array object or allocate space in memory; it creates a variable with a reference to an array Array variable declarations must indicate a dimension by using [] All arrays are zero-based Arrays must be indexed by int values or byte, short or char values (as these can be promoted to int) Using a long index value to access an array causes a compile error Attempting to access an array with an index less than 0 or greater than the length of the array causes an ArrayIndexOutOfBoundsException to be thrown at runtime Since arrays are Objects they can be initialized using the new operator When created, arrays are automatically initialized with the default value of their type Array references declared as members are initialized to null BUT array references declared in methods are not initialized Lecture/core/array/06 Page #1 feel the Technology…
- 2. Core Java Debasish Pratihari Examples of valid array declarations : String[]s; String s[]; String[][]s; String s[][]; String[] s[]; Initializing Array : String[ ] s = new String[100]; // default values: null boolean[] b = new boolean[4]; // default values: false int i[ ]= new int[5]; int[][] i = new int[10][10]; // default values: 0 String[] oneDimArray = { "abc","def","xyz" }; int[] array = null; int[][] twoDimArray = { {1,2,3}, {4,5,6}, {7,8,9} }; int[] a = { 1, primes[2], c, (int)Math.pow(2,2) }; int[] arr = new int[] {1,2,3}; int[][] myArray = new int[5][]; int arrSize = 100; String[] myArray = new String[arrSize]; Illegal Initialization of Array : String[5] s; int[] array = new int[]; int[][] myArray = new int[][5]; String[] s; s = { "Lakshya", "debasish", "java"}; Lecture/core/array/06 Page #2 feel the Technology…
- 3. Core Java Debasish Pratihari Finding length of an Array : Arrays have a length data field (read only), specifying the number of elements in the array. The length data field can be accessed through the dot operator. The bounds of an array are integers between 0 and length – 1 Example for ( int k=0; k < a.length ; k++ ) System.out.println( a[ k ] ); Multidimensional Arrays: Multidimensional arrays are implemented as arrays of arrays. Multidimensional arrays are declared by appending the appropriate number of bracket pairs after the array name. The number of elements in each direction need not be specified in the declaration. The number of elements in each direction need not be equal. Example of irregular Array : int[][] irregular = { { 1 }, { 2, 3 }, { 4, 5, 6, 7 }, {0} }; Lecture/core/array/06 Page #3 feel the Technology…
- 4. Core Java Debasish Pratihari An Example -Triangle Array : Output int[][] triangle = new int[10][]; for ( int j = 0; j<triangle.length ; j++ ) triangle[ j ] = new int[ j + 1 ]; for ( int i = 0 ; i < triangle.length ; i++ ) { for ( int j = 0 ; j < triangle[i].length ; j++ ) System.out.print( triangle[i][j] + " " ); System.out.println(); } 0 00 000 0000 00000 000000 0000000 00000000 000000000 0000000000 Coping Array : 25% Arrays can be copied using the Java System method arraycopy(): Signature:public static native void arraycopy(Object src, int src_position, Object dst, int dst_position, int length) Parameters: src - the source array. src_position - start position (first cell to copy) in the source array. dst - the destination array. dst_position - start position in the destination array. length - the number of array elements to be copied. By default, all Java arrays support the clone method. Things to Remember : An array is a container object that holds a fixed number of values of a single type. The length of an array is established when the array is created. After creation, its length is fixed. Each item in an array is called an element each element is accessed by its numerical index. Lecture/core/array/06 Page #4 feel the Technology…