Arrays

One-dimensional Arrays:

A list of items can be given one variable name using only one subscript and such a variable is called a single-subscripted variable or  a one dimensional array.

            Ex: x[0],x[1],x[2],…………, x[n]

The subscript can begin with 0 or 1

Like any other variable arrays must be declared and created in the computer memory before they are used. Creation of an array involves 3 steps:

1.                  Declare the array

2.                  Create memory locations

3.                  Put values into the memory location

Declaration of arrays:

Arrays in java may be declared in two forms:

Form1:  type arrayname[ ];

Form2:  type [ ] arrayname;

Examples:

int                    number[ ];

float                 average[ ];

int[ ]                 counter;

float[ ] marks;

Remember that we do not enter the size of the arrays in declaration.

Creation of arrays:

After declaration of an array we need to create it ion memory. Java allows us to create arrays using new operator only. As shown below:

                                    arrayname= new type[size];

Example:

            number            =          new int[5];

            average            =          new float[10];

Initialization of Arrays:

The final step is to put values into the array created. This process is known as initialization this done using the array subscripts as shown below:

                        Arrayname[subscript]=value;

Example:

number[0]=35;

number[1]=40;

…………………

…………………

number[4]=19;

note: java creates arrays starting with a subscript of 0 and ends with a value one less than the size specified.

We can also initialize arrays automatically  in the same way as the ordinary variables when they are declared, as shown below:

type arrayname[  ] = { list of values };

Example:

                        int number[ ] = { 35,40,20,57,19 };

Array length

In java all arrays store the allocated size in a variable named length.

Example: we can access the length of the array A is

            int Asize=A.length;

import java.io.*;

class array1

{

public static void main(String args[]) throws Exception

{

BufferedReader br=new BufferedReader(new InputStreamReader(System.in));

Float [ ]a =new Float [5];

Float x[ ]=new Float[5];

int i,j=0;

System.out.println("enter how many");

int n=Integer.parseInt(br.readLine());

System.out.println("enter the array elements");

for(i=0;i<n;i++)

{

a[i]=Float.valueOf(br.readLine());

}

System.out.println("  given array is....");

for(i=0;i<n;i++)

{

System.out.println("element at index "+ i +"   is  " +a[i]);

}

}

}

OUTPUT::

D:\ \programs>javac array1.java

D:\ \programs>java array1

enter how many

5

enter the array elements

1.1

1.2

1.3

1.4

1.5

given array is....

element at index 0   is  1.1

element at index 1   is  1.2

element at index 2   is  1.3

element at index 3   is  1.4

element at index 4   is  1.5

Two dimensional Arrays:

            For creating two-dimensional arrays we must follow the same steps as that of simple arrays. We may create a two dimensional array like this:

                        int myArray[ ][ ];

                        myArray = new int[3][4];

                                    (or)

                        int myArray[ ][ ]=new int [3][4];

The following example is for addition two matrices:

import java.io.*;

class matrix1

{

public static void main(String args[])throws IOException

{

int a[ ][ ]=new int [3][3];

int b[ ][ ]=new int [3][3];

int c[ ][ ]=new int [3][3];

int i,j;

BufferedReader br=new BufferedReader(new InputStreamReader(System.in));

System.out.println("enter how many rows and columns for matrix A:");

int m=Integer.parseInt(br.readLine());

int n= Integer.parseInt(br.readLine());

System.out.println("enter the lements into matrix:A");

for( i=0;i<m;i++)

{

for( j=0;j<n;j++)

{

a[i][j]=Integer.parseInt(br.readLine());

}

}

System.out.println("enter how many rows and columns for matrix B:");

int p=Integer.parseInt(br.readLine());

int q= Integer.parseInt(br.readLine());

System.out.println("enter the lements into matrix:B");

for( i=0;i<p;i++)

{

for( j=0;j<q;j++)

{

b[i][]=Integer.parseInt(br.readLine());

}

}

if(m!=p&&n!=q)

{

System.out.println("Addition is not Possible");

System.exit(0);

}

else

{

for(i=0;i<m;i++)

{

for(j=0;j<n;j++)

{

c[i][j]=a[i][j]+b[i][j];

}

}

}

System.out.println("result matrix is...");

for(i=0;i<m;i++)

{

System.out.println();

for(j=0;j<n;j++)

{

System.out.print("\t"+c[i][j]);

}

}

}

}

Output:

D:\ \programs>javac matrix1.java

D:\ \programs>java matrix1

enter how many rows and columns for matrix A:

2

2

enter the lements into matrix:A

1

2

3

4

enter how many rows and columns for matrix B:

2

2

enter the lements into matrix:B

1

2

3

4

result matrix is...

        2       4

        6       8