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Programming in Java
Lecture 10: Arrays
Array
• Definition:
An array is a group/collection of variables of the
same type that are referred to by a common name.
• Arrays of any type can be created and may have one
or more dimensions.
• A specific element in an array is accessed by its index
(subscript).
• Examples:
• Collection of numbers
• Collection of names
• Collection of suffixes
Array of numbers:
Array of names:
Array of suffixes:
Examples
10 23 863 8 229
ment tion ness ves
Sam Shanu Riya
One-Dimensional Arrays
• A one-dimensional array is a list of variables of same
type.
• The general form of a one-dimensional array
declaration is:
type var-name[ ]; array-var = new type[size];
or, type var-name[ ] = new type[size];
Example:
int num [] = new int [10];
Declaration of array variable:
data-type variable-name[];
eg. int marks[];
This will declare an array named ‘marks’ of type ‘int’. But no memory is
allocated to the array.
Allocation of memory:
variable-name = new data-type[size];
eg. marks = new int[5];
This will allocate memory of 5 integers to the array ‘marks’ and it can store
upto 5 integers in it. ‘new’ is a special operator that allocates memory.
Syntax
Accessing elements in the array:
• Specific element in the array is accessed by specifying
name of the array followed the index of the element.
• All array indexes in Java start at zero.
variable-name[index] = value;
Example:
marks[0] = 10;
This will assign the value 10 to the 1st
element in the array.
marks[2] = 863;;
This will assign the value 863 to the 3rd
element in the array.
STEP 1 : (Declaration)
int marks[];
marks  null
STEP 2: (Memory Allocation)
marks = new int[5];
marks 
marks[0] marks[1] marks[2] marks[3] marks[4]
STEP 3: (Accessing Elements)
marks[0] = 10;
marks 
marks[0] marks[1] marks[2] marks[3] marks[4]
Example
0 0 0 0 0
10 0 0 0 0
• Size of an array can’t be changed after the array is created.
• Default values:
– zero (0) for numeric data types,
– u0000 for chars and
– false for boolean types
• Length of an array can be obtained as:
array_ref_var.length
Example
class Demo_Array
{
public static void main(String args[])
{
int marks[];
marks = new int[3];
marks[0] = 10;
marks[1] = 35;
marks[2] = 84;
System.out.println(“Marks of 2nd
student=” + marks[1]);
}
}
• Arrays can store elements of the same data type. Hence an
int array CAN NOT store an element which is not an int.
• Though an element of a compatible type can be converted
to int and stored into the int array.
eg. marks[2] = (int) 22.5;
This will convert ‘22.5’ into the int part ‘22’ and store it into the 3rd
place
in the int array ‘marks’.
• Array indexes start from zero. Hence ‘marks[index]’ refers
to the (index+1)th
element in the array and ‘marks[size-1]’
refers to last element in the array.
Note
Array Initialization
1. data Type [] array_ref_var = {value0, value1, …, value n};
2. data Type [] array_ref_var;
array_ref_var = {value0, value1, …,value n};
3. data Type [] array_ref_var = new data Type [n+1];
array_ref_var [0] = value 0;
array_ref_var [1] = value 1;
…
array_ref_var [n] = value n;
Multi-Dimensional Array
• Multidimensional arrays are arrays of arrays.
• Two-Dimensional arrays are used to represent a table or a
matrix.
• Creating Two-Dimensional Array:
int twoD[][] = new int[4][5];
Conceptual View of 2-Dimensional Array
class TwoDimArr
{
public static void main(String args[])
{
int twoD[][]= new int[4][5];
int i, j, k = 0;
for(i=0; i<4; i++)
for(j=0; j<5; j++)
{
twoD[i][j] = k;
k++;
}
for(i=0; i<4; i++)
{
for(j=0; j<5; j++)
System.out.print(twoD[i][j] + " ");
System.out.println();
}
}
}
• When we allocate memory for a multidimensional
array, we need to only specify the memory for the
first (leftmost) dimension.
int twoD[][] = new int[4][];
• The other dimensions can be assigned manually.
// Manually allocate differing size second dimensions.
class TwoDAgain {
public static void main(String args[]) {
int twoD[][] = new int[4][];
twoD[0] = new int[1];
twoD[1] = new int[2];
twoD[2] = new int[3];
twoD[3] = new int[4];
int i, j, k = 0;
for(i=0; i<4; i++)
for(j=0; j<i+1; j++)
{
twoD[i][j] = k;
k++;
}
for(i=0; i<4; i++) {
for(j=0; j<i+1; j++)
System.out.print(twoD[i][j] + " ");
System.out.println();
}
}
}
Initializing Multi-Dimensional Array
class Matrix {
public static void main(String args[]) {
double m[][] = {
{ 0*0, 1*0, 2*0, 3*0 },
{ 0*1, 1*1, 2*1, 3*1 },
{ 0*2, 1*2, 2*2, 3*2 },
{ 0*3, 1*3, 2*3, 3*3 }
};
int i, j;
for(i=0; i<4; i++) {
for(j=0; j<4; j++)
System.out.print(m[i][j] + " ");
System.out.println();
}
}
}
Alternative Array Declaration
type[ ] var-name;
• Example:
char twod1[][] = new char[3][4];
char[][] twod2 = new char[3][4];
• This alternative declaration form offers convenience
when declaring several arrays at the same time.
• Example: int[] nums, nums2, nums3;
Array Cloning
• To actually create another array with its own values,
Java provides the clone()method.
• arr2 = arr1; (assignment)
is not equivalent to
arr2 = arr1.clone(); (cloning)
Example: ArrayCloning.java
Array as Argument
• Arrays can be passed as an argument to any method.
Example:
void show ( int []x) {}
public static void main(String arr[]) {}
void compareArray(int [] a, int [] b ){}
Array as a return Type
• Arrays can also be returned as the return type of any
method
Example:
public int [] Result (int roll_No, int marks )
Assignment for Practice
• WAP in which use a method to convert all the double
values of argumented array into int.
public int[] double_To_Int(double [] ar)
• WAP to create a jagged Array in which rows and
columns should be taken as input from user.
L10 array

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L10 array

  • 2. Array • Definition: An array is a group/collection of variables of the same type that are referred to by a common name. • Arrays of any type can be created and may have one or more dimensions. • A specific element in an array is accessed by its index (subscript). • Examples: • Collection of numbers • Collection of names • Collection of suffixes
  • 3. Array of numbers: Array of names: Array of suffixes: Examples 10 23 863 8 229 ment tion ness ves Sam Shanu Riya
  • 4. One-Dimensional Arrays • A one-dimensional array is a list of variables of same type. • The general form of a one-dimensional array declaration is: type var-name[ ]; array-var = new type[size]; or, type var-name[ ] = new type[size]; Example: int num [] = new int [10];
  • 5. Declaration of array variable: data-type variable-name[]; eg. int marks[]; This will declare an array named ‘marks’ of type ‘int’. But no memory is allocated to the array. Allocation of memory: variable-name = new data-type[size]; eg. marks = new int[5]; This will allocate memory of 5 integers to the array ‘marks’ and it can store upto 5 integers in it. ‘new’ is a special operator that allocates memory. Syntax
  • 6. Accessing elements in the array: • Specific element in the array is accessed by specifying name of the array followed the index of the element. • All array indexes in Java start at zero. variable-name[index] = value; Example: marks[0] = 10; This will assign the value 10 to the 1st element in the array. marks[2] = 863;; This will assign the value 863 to the 3rd element in the array.
  • 7. STEP 1 : (Declaration) int marks[]; marks  null STEP 2: (Memory Allocation) marks = new int[5]; marks  marks[0] marks[1] marks[2] marks[3] marks[4] STEP 3: (Accessing Elements) marks[0] = 10; marks  marks[0] marks[1] marks[2] marks[3] marks[4] Example 0 0 0 0 0 10 0 0 0 0
  • 8. • Size of an array can’t be changed after the array is created. • Default values: – zero (0) for numeric data types, – u0000 for chars and – false for boolean types • Length of an array can be obtained as: array_ref_var.length
  • 9. Example class Demo_Array { public static void main(String args[]) { int marks[]; marks = new int[3]; marks[0] = 10; marks[1] = 35; marks[2] = 84; System.out.println(“Marks of 2nd student=” + marks[1]); } }
  • 10. • Arrays can store elements of the same data type. Hence an int array CAN NOT store an element which is not an int. • Though an element of a compatible type can be converted to int and stored into the int array. eg. marks[2] = (int) 22.5; This will convert ‘22.5’ into the int part ‘22’ and store it into the 3rd place in the int array ‘marks’. • Array indexes start from zero. Hence ‘marks[index]’ refers to the (index+1)th element in the array and ‘marks[size-1]’ refers to last element in the array. Note
  • 11. Array Initialization 1. data Type [] array_ref_var = {value0, value1, …, value n}; 2. data Type [] array_ref_var; array_ref_var = {value0, value1, …,value n}; 3. data Type [] array_ref_var = new data Type [n+1]; array_ref_var [0] = value 0; array_ref_var [1] = value 1; … array_ref_var [n] = value n;
  • 12. Multi-Dimensional Array • Multidimensional arrays are arrays of arrays. • Two-Dimensional arrays are used to represent a table or a matrix. • Creating Two-Dimensional Array: int twoD[][] = new int[4][5];
  • 13. Conceptual View of 2-Dimensional Array
  • 14. class TwoDimArr { public static void main(String args[]) { int twoD[][]= new int[4][5]; int i, j, k = 0; for(i=0; i<4; i++) for(j=0; j<5; j++) { twoD[i][j] = k; k++; } for(i=0; i<4; i++) { for(j=0; j<5; j++) System.out.print(twoD[i][j] + " "); System.out.println(); } } }
  • 15. • When we allocate memory for a multidimensional array, we need to only specify the memory for the first (leftmost) dimension. int twoD[][] = new int[4][]; • The other dimensions can be assigned manually.
  • 16. // Manually allocate differing size second dimensions. class TwoDAgain { public static void main(String args[]) { int twoD[][] = new int[4][]; twoD[0] = new int[1]; twoD[1] = new int[2]; twoD[2] = new int[3]; twoD[3] = new int[4]; int i, j, k = 0; for(i=0; i<4; i++) for(j=0; j<i+1; j++) { twoD[i][j] = k; k++; } for(i=0; i<4; i++) { for(j=0; j<i+1; j++) System.out.print(twoD[i][j] + " "); System.out.println(); } } }
  • 17. Initializing Multi-Dimensional Array class Matrix { public static void main(String args[]) { double m[][] = { { 0*0, 1*0, 2*0, 3*0 }, { 0*1, 1*1, 2*1, 3*1 }, { 0*2, 1*2, 2*2, 3*2 }, { 0*3, 1*3, 2*3, 3*3 } }; int i, j; for(i=0; i<4; i++) { for(j=0; j<4; j++) System.out.print(m[i][j] + " "); System.out.println(); } } }
  • 18. Alternative Array Declaration type[ ] var-name; • Example: char twod1[][] = new char[3][4]; char[][] twod2 = new char[3][4]; • This alternative declaration form offers convenience when declaring several arrays at the same time. • Example: int[] nums, nums2, nums3;
  • 19. Array Cloning • To actually create another array with its own values, Java provides the clone()method. • arr2 = arr1; (assignment) is not equivalent to arr2 = arr1.clone(); (cloning) Example: ArrayCloning.java
  • 20. Array as Argument • Arrays can be passed as an argument to any method. Example: void show ( int []x) {} public static void main(String arr[]) {} void compareArray(int [] a, int [] b ){}
  • 21. Array as a return Type • Arrays can also be returned as the return type of any method Example: public int [] Result (int roll_No, int marks )
  • 22. Assignment for Practice • WAP in which use a method to convert all the double values of argumented array into int. public int[] double_To_Int(double [] ar) • WAP to create a jagged Array in which rows and columns should be taken as input from user.

Notas do Editor

  1. int i = 7; int j = 2; int k = 4; v[0] = 1; // element 0 of v given value 1 v[i] = 5; // element i of v given value 5 v[j] = v[i] + 3; // element j of v given value // of element i of v plus 3 v[j+1] = v[i] + v[0]; // element j+1 of v given value // of element i of v plus // value of element 0 of v v[v[j]] = 12; // element v[j] of v given // value 12 System.out.println(v[2]); // element 2 of v is displayed v[k] = Integer.parseInt(stdin.readLine()); // element k of v given next // extracted value
  2. int i = 7; int j = 2; int k = 4; v[0] = 1; // element 0 of v given value 1 v[i] = 5; // element i of v given value 5 v[j] = v[i] + 3; // element j of v given value // of element i of v plus 3 v[j+1] = v[i] + v[0]; // element j+1 of v given value // of element i of v plus // value of element 0 of v v[v[j]] = 12; // element v[j] of v given // value 12 System.out.println(v[2]); // element 2 of v is displayed v[k] = Integer.parseInt(stdin.readLine()); // element k of v given next // extracted value
  3. int i = 7; int j = 2; int k = 4; v[0] = 1; // element 0 of v given value 1 v[i] = 5; // element i of v given value 5 v[j] = v[i] + 3; // element j of v given value // of element i of v plus 3 v[j+1] = v[i] + v[0]; // element j+1 of v given value // of element i of v plus // value of element 0 of v v[v[j]] = 12; // element v[j] of v given // value 12 System.out.println(v[2]); // element 2 of v is displayed v[k] = Integer.parseInt(stdin.readLine()); // element k of v given next // extracted value
  4. int i = 7; int j = 2; int k = 4; v[0] = 1; // element 0 of v given value 1 v[i] = 5; // element i of v given value 5 v[j] = v[i] + 3; // element j of v given value // of element i of v plus 3 v[j+1] = v[i] + v[0]; // element j+1 of v given value // of element i of v plus // value of element 0 of v v[v[j]] = 12; // element v[j] of v given // value 12 System.out.println(v[2]); // element 2 of v is displayed v[k] = Integer.parseInt(stdin.readLine()); // element k of v given next // extracted value
  5. int i = 7; int j = 2; int k = 4; v[0] = 1; // element 0 of v given value 1 v[i] = 5; // element i of v given value 5 v[j] = v[i] + 3; // element j of v given value // of element i of v plus 3 v[j+1] = v[i] + v[0]; // element j+1 of v given value // of element i of v plus // value of element 0 of v v[v[j]] = 12; // element v[j] of v given // value 12 System.out.println(v[2]); // element 2 of v is displayed v[k] = Integer.parseInt(stdin.readLine()); // element k of v given next // extracted value
  6. int i = 7; int j = 2; int k = 4; v[0] = 1; // element 0 of v given value 1 v[i] = 5; // element i of v given value 5 v[j] = v[i] + 3; // element j of v given value // of element i of v plus 3 v[j+1] = v[i] + v[0]; // element j+1 of v given value // of element i of v plus // value of element 0 of v v[v[j]] = 12; // element v[j] of v given // value 12 System.out.println(v[2]); // element 2 of v is displayed v[k] = Integer.parseInt(stdin.readLine()); // element k of v given next // extracted value
  7. int i = 7; int j = 2; int k = 4; v[0] = 1; // element 0 of v given value 1 v[i] = 5; // element i of v given value 5 v[j] = v[i] + 3; // element j of v given value // of element i of v plus 3 v[j+1] = v[i] + v[0]; // element j+1 of v given value // of element i of v plus // value of element 0 of v v[v[j]] = 12; // element v[j] of v given // value 12 System.out.println(v[2]); // element 2 of v is displayed v[k] = Integer.parseInt(stdin.readLine()); // element k of v given next // extracted value
  8. int i = 7; int j = 2; int k = 4; v[0] = 1; // element 0 of v given value 1 v[i] = 5; // element i of v given value 5 v[j] = v[i] + 3; // element j of v given value // of element i of v plus 3 v[j+1] = v[i] + v[0]; // element j+1 of v given value // of element i of v plus // value of element 0 of v v[v[j]] = 12; // element v[j] of v given // value 12 System.out.println(v[2]); // element 2 of v is displayed v[k] = Integer.parseInt(stdin.readLine()); // element k of v given next // extracted value