Java Array Definition (One-dimensional and Multidimensional Arrays)


One-Dimensional Arrays

As in all programming languages, the array structure in Java is an important data structure in the last place. Briefly describing the structure of the array:

An array is a data structure that stores a large number of data, usually of the same type, in the computer memory under the same name. The following is a logical view of an index named x:

4  2    7 22 11 3
0 1 2 3 4 5

The index has a name and an index that indicates how many elements in the array are indexed. For example, for the array x above, the expression x represents the element number 3 in this directory, which is 22. The index of the index is always specified in square brackets in the Java language.

  • The index of the first element of an array in the Java language is always 0; and the index of the last element is equal to 1 minus the number of places left in the sequence.
  • The type, name, and maximum number of elements of the index are specified in a declaration statement:

or equivalent

For example, for the above x array,

The x array is 6 elements and the elements are of type int.

What is required for the array?

We need it in practice when it is necessary to keep a data set of the same type entirely in memory. For example, applications such as sorting of data, calculation of some statistical information of a data set (standard deviation, etc.) are such applications.

Example: Here are two different Java programs that do the same thing. Both programs collect the total of 5 numbers entered on the computer.

Demo

  • NOTE: The Scanner class is used to assign a variable from a stream. The System.in stream is used to input user’s console data.

Array Initial Value Assignment

As with many computer languages, it is possible to assign an initial value in the Java language when defining the sequence index. For example;

The following values are assigned to the x sequence: Example: Initial Value Assignment

Here we will have the following output:

Another method in array definition

After defining the array size as a variable, it is also possible to use this variable when defining the array. It can define a 5-element array with the following commands, but we can not assign the first value to the array:

Multidimensional Arrays

The most common use for multi-dimensional arrays is for two-dimensional arrays.

Let us present the following data:

brand january february march
Fiat 700 600 650
Renault 900 800 700
VW 300 400 350
Opel 500 450 470
Ford 600 500 480

In the Java language, we can store the tabular information in a structure called a two dimensional array structure in computer memory. This natural type of mathematical matrix structures in Java is also a two dimensional array structure.

In Java, we can define this table, which consists of 5 rows and 3 columns, as follows:

Here we use an expression in the program to refer to an element of a two-dimensional array called sales. Here, the name of the sales directory, i is the row index, and j is the index of the column. The row index of the satis sequence starts at 0 and continues until 4. Column indices are between 0 and 2. Here’s how the sales line is stored in memory in Java:

Accordingly, the sales [0,0] element is 700, the sales [2,1] element is 400, and the sales [4,2] element is 480.
The number of elements in a two-dimensional array called sat = 5×3 = 15.

To read two dimensional array elements

We can use a program such as the following to input elements of the two-dimensional array from the keyboard during execution of the Java program. In the following example program, 3 rows and 2 columns of sales are entered from the keyboard and then the table is transferred to the screen. Now let’s examine this sample program:

Using the length function

With the length function, it is possible to find the number of elements in each dimension of the two-dimensional array.

For Example:

Matrix Multiplication

The following Java program,

Cmn = Amk Bkn

matrix multiplication

Output:

EXAMPLE: Develop a Java program that automatically generates and prints the following matrix.

( 2! – 1 ) / 3 ( 4! + 2 ) / 5 ( 6! – 3 ) / 7
( 8! + 4 ) / 9 ( 10! – 5 ) / 11 ( 12! + 6 ) / 13

Output:

 

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