Java arrays

Arrays
 Step1 : Create a reference. Cannot mention
the size.
◦ Datatype [ ] arrname;
◦ Datatype arrname[ ]; Valid – not recommended
 Step 2 : Reserve memory
◦ arrname = new datatype[SIZE];
 Step3 : Access elements
 Array index begins from 0.
 int [] a = {5 , 8 , 10}; //Valid (decl + def).
mohammed.sikander@cranessoftware.
com 2

Arrays
int [] a , b;
int c [ ] , d;
a and b; both are arrays
c is array and d is not a array

Arrays
To know the number of elements
Arr.length
int [ ] arr1 = {3 , 9 , 1, 4 , 7 };
System.out.println(arr1.length);
int [ ] arr2;
int [ ] arr3;
arr3 = new int[10];

Array - Accessing elements
 Method 1 :
 Find Length : arr.length
 for(int index = 0; index < arr.length ; index++)
 System.out.println(arr[index]);
 Method 2:
 for(int x : arr)
 System.out.println(x);
mohammed.sikander@cranessoftware.
com 5

int [ ] arr = {3 , 9 , 1, 4 , 7 };
for(int val : arr)
System.out.println(val);
float [ ] arr = {3 , 9 , 1, 4 , 7 };
for(float val : arr)
int [ ] arr = {3 , 9 , 1, 4 , 7 };
int val;
for(val : arr)

Can we use == to compare
arrays?
int [] arr1 = {7 , 5 , 2 , 8};
int [] arr2 = {7 , 5 , 2 , 8};
if(arr1 == arr2)
System.out.println("Equal");
else
System.out.println("Not Equal");

1. int [] arr1 = {7 , 5 , 2 , 8};
2. int [] arr2 ;
3. arr2 = arr1;
4. if(arr1 == arr2)
5. System.out.println("Equal");
6. else
7. System.out.println("Not
Equal");
Can we use == to compare
arrays?

Can we assign character variable to
integer?
1. char c = 'A';
2. int x = c;
Can we assign from character array to
integer array?
3. char [] carr = {'S','I','K'};
4. int [] iarr = carr;

 int [] arr;
 arr = new int[5];
 arr[0] = 12;
 arr[1] = 23;
 arr[2] = 34;

 for(int i = 0 ; i < arr.length ; i++)
 System.out.println(arr[i]);

Multi-dimensional Array
 int [] [] marks;
 int row = 3;
 int col = 4;
 marks = new int[row][col];
 for(int i = 0 ; i < row ; i++)
 for(int j = 0 ; j < col ; j++)
 marks[i][j] = i + j;

Multi-dimensional Arrays
 Method1 : Declare and initialise
 int [][] a = { {1 , 2 , 3 , 4} , {5,6,7} , {8}};
 1st row has 4 col, 3rd row has 1 col.
 System.out.println("No. of Rows = " + a.length);
 for(int x = 0 ; x < a.length ; x++)
 System.out.println("No. of Columns in " + x + " = " +
a[x].length);
 for(int r = 0 ; r < a.length ; r++)
 {
 for(int c = 0 ; c < a[r].length ; c++)
 System.out.print(a[r][c] + " ");
 } mohammed.sikander@cranessoftware.
com 12

 int [] [] marks;
 int row = 3;
 int col = 4;
 marks = new int[row][];

 for(int i = 0 ; i < row ; i++)
 for(int j = 0 ; j < col ; j++)
 marks[i][j] = i + j;
for(int i = 0 ; i < row ; i++)
marks[i] = new int[col];
Multi-dimensional Array

Multi-Dimensional Array
 int [][] mat = {{5 , 8 , 9 } , {2 , 4 } , {6}};
 mat[0][0]
 mat[0][1]
 mat[0][2]
 mat[1][0]
 mat[1][1]
 mat[1][2]
 mat[2][0]
 mat[2][1]
 mat[2][2]
 mat[0][0]
 mat[0][1]
 mat[0][2]
 mat[1][0]
 mat[1][1]
 mat[1][2]
 mat[2][0]
 mat[2][1]
 mat[2][2]

Copying Arrays
int [] arr1 = {5 ,8 , 10, 15, 20};
int [] arr2;
arr2 = arr1;
for(int x: arr2)
System.out.println(x);
arr1[0] = 2; arr1[1] = 4;
for(int x: arr2)

 System.arraycopy(src Array, src pos,
destination Array, dest pos, length);
 int [] arr1 = {5 ,8 , 10, 15, 20};
 int [] arr2 = new int[5];

 System.arraycopy(arr1, 0, arr2, 0, 5);

int [] arr1 = {5 ,8 , 10, 15, 20};
int [] arr2 = Arrays.copyOf(arr1, 5);
for(int x: arr2)

Sorting of Array
 Arrays.sort(Type [] arr);
 Arrays.sort(Type [], int fromIndex, int toIndex);
 int arr[] = {5,2,9,1,2,8};
 Arrays.sort(arr); OR
 Arrays.sort(arr,0,6);
 Output : 1 2 2 5 8 9
 int arr[] = {5,2,9,1,2,8};
 Arrays.sort(arr,1,5);
 Output : 5 1 2 2 9 8

Anonymous Arrays
public static void printArray(int [] x)
{
for(int i : x)
}
public static void main(String [] args)
{
int [] marks = {3,6,4,7};
1. printArray(marks);
2. printArray(1 ,3 ,5 ,7);
3. printArray([]{1 ,3 ,4 ,5});
4. printArray(new int []{1 ,3 ,4 ,5});
}
Identify the valid calls to
printArray?

Argument Passing
public static void function(int x)
{
x = 20;
System.out.println("Function " + x);
}
{
int x = 5;
function(x);
System.out.println("Main " + x);
}

Passing Array to Function
public class ArgumentPassingArray {
public static void function(int [] arr)
{
arr[0] = 20;
}
{
int [] arr = {5,8,10};
function(arr);
System.out.println("Main " + arr[0]);
}
}

String str;
str = new String("SIKANDER");
System.out.println(str.hashCode());
str = str.toLowerCase();
System.out.println(str.hashCode());

Argument Passing to Function
class Rectangle {
int length ;
int breadth;
Rectangle(int l , int b) {
length = l ;
breadth = b;
}
}
public class FunctionDemo {
public static void function(Rectangle x)
{
x.length = 20;
System.out.println("Function " + x.length + " " + x.breadth);
}
{
Rectangle obj = new Rectangle(4 ,5 );
function(obj);
System.out.println("Main " + obj.length + " " + obj.breadth);
}
}

class Rectangle {
int length ;
int breadth;
Rectangle(int l , int b) {
length = l ;
breadth = b;
}
}
public class FunctionDemo {
public static void function(Rectangle x)
{
x = new Rectangle( 7 , 9);
System.out.println("Function " + x.length + " " + x.breadth);
}
{
Rectangle obj = new Rectangle(4 ,5 );
function(obj);
System.out.println("Main " + obj.length + " " + obj.breadth);
}
}

Java arrays

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