Arrays in jAVA

Arrays in jAVA

OBJECTIVE

Study Java One and Two Dimentional Arrays.

THEORY

Arrays

array is a group of like-typed variables 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. Arrays offer a convenient means of grouping related information.

One Dimensional Arrays

A one-dimensional array is, essentially, a list of like-typed variables. To create an array, you first must create an array variable of the desired type. The general form of a one dimensional array declaration is

int month_days[];

This declaration establishes the fact that month_days is an array variable,

no array actually exists. In fact, the value of month_days is set to null, which represents an array with no value. To link month_days with an actual, physical array of integers, you must allocate one using new and assign it to month_days. new is a special operator that allocates memory.

The general form of new as it applies to one-dimensional arrays appears as follows:

array-var = new type[size];

It is possible to combine the declaration of the array variable with the allocation of

the array itself, as shown here:

int month_days[] = new int[12];

Prorgam 1

program fill an array of 10 elements by randomly generated Integers,

range (1-100).

import java.lang.Math;

public class array1

{

   public static void main(String args[])

   {

      int a[] = new int [10];

      for (int i=0;i<10;i++)

         a[i]=(int)(Math.random()*100);

    

      System.out.println("Values are");

      for (int i=0;i<10;i++)

          System.out.println(a[i]);

   }

}

Output:

 

Multidimensional Arrays

Java, multidimensional arrays are actually arrays of arrays. These, as you might

expect, look and act like regular multidimensional arrays.

For example, the following declares a two-dimensional array variable called twoD.

int twoD[][] = new int[4][5];

 

possible to initialize multidimensional arrays. To do so, simply enclose each

dimension’s initializer within its own set of curly braces. following program creates a matrix where each element contains the product of the row and column indexes. Also notice that you can use expressions as well as literal values inside of array initializers.

// Initialize a two-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();

}

}

}

Output:

---

When you allocate memory for a multidimensional array, you need only specify the

memory for the first (leftmost) dimension. You can allocate the remaining dimensions

separately.

when you allocate dimensions manually, you do not need to allocate the same number of elements for each dimension. As stated earlier, since multidimensional arrays are actually arrays of arrays, the length of each array is under your control. For example, the following program creates a two dimensional array in which the sizes of the second dimension are unequal.

Prorgam 2

program manually allocate differing size second dimensions.

public class array2 {

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();

}

}

}

Output: