Arrays In Java

Arrays In Java


Arrays:It can be defined as the collection of similar elements together . Array Size Starts from "0" and ends at "n-1"

Example: 
  1. Collection of student roll numbers comes under one single integer array.
  2. Collection of student names comes under one single String array.
  3. Collection of Faculty salarys comes under one single Float array.

Types Of Arrays:

There are three types of arrays they are :
  1. One/Single dimensional array
  2. Two Dimensional array
  3. Multi Dimensional array
1.One/Single Dimensional Array:

One Dimensional array is used to collect the set of elements together . The Size of the array can be defined as "Product of number of bytes of datatype and size of the array."

 Size of an array= number of bytes used by datatype * size of the array.

Syntax:

Initializing an array:

<datatype>[] variable={values};

Example for initializing :

int[] a={10,20,30,40};

Declaring an array:

<datatype>[] variable=new <datatype>[size];

Example for declaration:

int[] a=new int[3];

Program for  1-Dimensional Array By Passing Values at Compile time

class SingleDeimension
{
public static void main(String[] args) 
{
int[] a={10,20,30,40};
System.out.println("values:");

for(int i=0;i<a.length;i++)
{
System.out.println(a[i]);
}
}
}

Save as:

 SingleDeimension.java

Compile:

javac  SingleDeimension.java

Run:

java  SingleDeimension

Output:

values:
10
20
30
40

Note:

Length is used to return the length of an array . The memory can be allocated and de-allocated automatically in java .

Program for 1-Dimensional Array By Passing size at Compile time

import java.util.Scanner;

 class SingleDeimensionDec
{
public static void main(String[] args) 
{
int[] a=new int[5];                   //Size of array has been initialized

Scanner sc=new Scanner(System.in);

 System.out.println("Enter 5 values");

 for(int i=0;i<a.length;i++)
{
a[i]=sc.nextInt();
}

 System.out.println("5 values are:");

for(int i=0;i<a.length;i++)
{
System.out.println(a[i]);
}
}

}

Save as:

 SingleDeimensionDec.java

Compile:

javac  SingleDeimensionDec.java

Run:

java  SingleDeimensionDec

 Input:

 Enter 5 values:
10
20
30
40
50

Output:

5 values:
10
20
30
40

Note:

From the above program we have declared the array variable passing the value of size at compile time .For every time of execution the size of array remains constant so to avoid this problem we have take the size of the array from the user at run Time .

Program for One Dimensional Array By Passing size at run time

import java.util.Scanner;

 class SingleDeimensionDec1
{
public static void main(String[] args) 
{
Scanner sc=new Scanner(System.in);

int size;                                                       //Size Of Array is passed at Run Time

 System.out.println("Enter size of array");

 size=sc.nextInt();

int[] a=new int[size];

System.out.println("Enter"+"\t"+size+"\t"+"values");

 for(int i=0;i<a.length;i++)
{
a[i]=sc.nextInt();
}

 System.out.println(size+"\t"+"values are:");

for(int i=0;i<a.length;i++)
{
System.out.println(a[i]);
}
}

}

Save as:

 SingleDeimensionDec1.java

Compile:

javac  SingleDeimensionDec1.java

Run:

java  SingleDeimensionDec1

 Input:

 Enter Size Value:
5

 Enter 5 values:
10
20
30
40
50

Output:

5 values:
10
20
30
40

Note:

In this the size value is passed at run time . Depending on size  values given , the memory is allocated .The size value is passed at Run Time . Can Differ from execution to execution .

2.Two Dimensional Array: 
           
It is also the collection of similar elements in the form of table/matrix representation . The size of the array is product of bytes of datatype and Sum of sizes (Rows+columns).
Size of two Dimensional Array = bytes of datatype * (Size of rows + Size of columns).

Syntax:

Initializing an array:

<datatype>[][] variable={{values of rows},{values of columns}};

Example for initializing :

int[][] a={{10,20,30,40},{1,2,3,4}};

Declaring an array:

<datatype>[][] variable=new <datatype>[size of rows][size of columns];

Example for declaration:

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

Program for 2-Dimensional Array By Passing values at run time

class DoubleDimensionInit
{
public static void main(String[] args) 
{
int[][] a={{10,20},{30,40}};                              //Values at Compile Time

System.out.println("values:");

 for(int i=0;i<a.length;i++)
{
     for(int j=0;j<a.length;j++)
     {
System.out.print(a[i][j]);

 System.out.print("\t");
     }

 System.out.println("");
}
}

}
Save as:

 DoubleDimensionInit.java

Compile:

javac  DoubleDimensionInit.java

Run:

java  DoubleDimensionInit

Output:

values:

10      20
30      40

 Note:

 From the above the size and the values are constant for every execution . since the values are passed at compile time.

Program for 2-Dimensional Array By Passing size at Compile time

import java.util.Scanner;

 class DoubleDimensionDec
{
public static void main(String[] args) 
{
int[][] a=new int[2][2];                        //Size at Compile Time
 
System.out.println("Enter the values for 2*2 matrix :");

Scanner sc=new Scanner(System.in);

 for(int i=0;i<a.length;i++)
{
     for(int j=0;j<a.length;j++)
     {
a[i][j]=sc.nextInt();
 }
}

 System.out.println("values:");

 for(int i=0;i<a.length;i++)
{
     for(int j=0;j<a.length;j++)
     {
System.out.print(a[i][j]);

 System.out.print("\t");
     }

 System.out.println("");
}
}

}

Save as:

 DoubleDimensionInit.java

Compile:

javac  DoubleDimensionInit.java

Run:

java  DoubleDimensionInit

Input:

 Enter the values for 2*2 matrix :

 10
20
30
40

 Output:

values:

10      20
30      40

 Note:

From the above program all the values are passed at run time but the problem is the size of matrix will be constant . This can be resolved by passing the size of matrix and values of the matrix at Run Time.

Program for Two Dimensional Array By Passing size at run time

import java.util.Scanner;

 class DoubleDimensionRun
{
public static void main(String[] args) 
{
int rows;
int col;

Scanner sc=new Scanner(System.in);

System.out.println("Enter the values rows and columns:");

rows=sc.nextInt();

 col=sc.nextInt();

 int[][] a=new int[rows][col];
 
System.out.println("Enter the values for"+rows+"*"+col+"matrix :");

for(int i=0;i<a.length;i++)
{
         for(int j=0;j<a.length;j++)
         {
a[i][j]=sc.nextInt();
   }
}

 System.out.println("values:");

 for(int i=0;i<a.length;i++)
{
     for(int j=0;j<a.length;j++)
     {
System.out.print(a[i][j]);

 System.out.print("\t");
     }

 System.out.println("");
}
}

}

Save as:

 DoubleDimensionInit.java

Compile:

javac  DoubleDimensionInit.java

Run:

java  DoubleDimensionInit

Input:

 Enter the values rows and columns:
2
2

Enter the values for 2*2 matrix :

10
20
30
40

Output:

values:
10      20

30      40

3.Multi Dimensional Array: This Type of arrays are generally not used. This are used to deal the objects related to space and when  we require more than 2- Dimensions.

 This type of arrays are not much needed to learn .

Passing Array As a Parameter


import java.util.Scanner;



class ArrayAsPara

{
void arraySwap(int ar[])
{
System.out.println("Swapped Values:");

for(int i=ar.length-1;i>=0;i--)
{
System.out.println(ar[i]);
}
}

}

class ArrayAsParaTest 
{
public static void main(String[] args) 
{
int size;
System.out.println("Enter size of array:");

Scanner sc=new Scanner(System.in);

size=sc.nextInt();

int a[]=new int[size];
System.out.println("Enter values of array:");

for(int i=0;i<a.length;i++)
{
a[i]=sc.nextInt();
}

ArrayAsPara aap=new ArrayAsPara();

aap.arraySwap(a);
}
}

Save as:

ArrayAsParaTest .java

Compile:

javac  ArrayAsParaTest.java

Run:

java  ArrayAsParaTest

Input:
Enter size of array:
2

Enter values of array:
10
20

Output:

Swapped Values:

20
10

Note:

Array can also be passed as a parameter to a method to use the same array for any operation.
Command Line Arguments:This are the values passed to the program before running the program after compilation. User can provide the values to this arguments.In this each value is separated by space between the value.

Syntax:

java FileName value1 value2 ........

Example:

java CommandLineArguments void main (enter key).

Program Using Command Line Arguments



class CommandLineArguments 
{
public static void main(String[] args) 
{
int n=args.length;
System.out.println("Command Line Arguments");

for(int i=0;i<n;i++)
{
System.out.println(args[i]);
}

}
}


Save as:

CommandLineArguments .java

Compile:

javac  CommandLineArguments .java

Run:

java  CommandLineArguments  VoidMainTechnologies Dilsuknagar

Output:

Dilsuknagar

Note:

From the above program we can see that we have passed two values at run time . By giving the space between the values they are considered as the different values .


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