How to declare Java array, creating java array, initialization and accessing java array elements?. An Array in Java is a container objects that holds a collection of similar type of elements (type may be integer, float, long etc). It means, we can’t store multiple data type values.
In our previous articles we seen the variable declaration, initialization and, they are pretty good for initializing few variables. What if we want to store 100 employees salary? Is it worth to create 100 variables and assign those values, What happen if it is 150 employees. In order to handle these type of situation, Java Programming language introduced the concept of arrays.
Java Array Introduction
For example, an integer array in Java will store all the integer elements, if you try to insert a float or char value then it will throw an error.
TIP: The length of a Java array is decided when we are creating an array. Once it is created, length is fixed
We have 3 types of arrays in Java Programming
- One Dimensional Array
- Two Dimensional Array
- Multi-Dimensional Array
- Three Dimensional Array
- Four Dimensional Array etc
Java array declaration or Syntax
The following code snippet will show you the most basic way of Java array declaration:
Data_Type[] Array_Name;
- Data_type: It will decide the type of elements array will accept. For example, If we want to store integer values then, the Data Type will be declared as int, If we want to store Float values then, the Data Type will be float etc
- Array_Name: This is the name you want to give it to array. For example students, age, marks, employees etc
Similarly you can declare the remaining type of arrays in Java as follows:
int [] anIntegerArray; // declaring an array of Integers byte[] anByteArray; // declaring an array of Bytes short[] anShortArray; // declaring an array of Shorts long[] anLongArray; // declaring an array of Longs float[] anFloatArray; // declaring an array of Floats double[] anDoubleArray; // declaring an array of Doubles boolean[] anBooleanArray; // declaring an array of Booleans char[] anCharArray; // declaring an array of Chars String[] anStringArray; // declaring an array of Strings
Create a Java Array
In order to create an array in Java, we have to use the New operator as we shown below:
Data_Type[] Array_Name = new Array_Name[Array_Size];
If you observe the above code snippet,
- Array_Size: Number of elements an array can hold or store. For example, Array_Size =10 then array will hold 10 values.
If you already initialized an array in java then
int [] anIntegerArray; // Java array declaration // Crating an Java Array anIntegerArray = new int[10];
For Example,
int[] Student_Marks = new int[10];
- Here, we used int as the data type to declare an array. So, above array will accept only integers. If you try to add float values then it will through an error.
- Student_Age is the array name
- The size of an Array is 10 it means, Student_Marks array will only accept 10 integer values.
- If we try to store more than 10 then it will throw an error.
- We can store less than 10. For Example, If we store 3 integer values then remaining 2 values will be initialized to default value (Which is 0).
Java Array Initialization
There are multiple ways to initialize the array in Java Programming language
First Approach
Declaring and Creating an Array in Java
int[] Student_Marks = new int[3];
Initializing Array elements in more traditional way
Student_Marks[0] = 15; // Initializing First array elements at position 0 Student_Marks[1] = 45; // Initializing First array elements at position 1 Student_Marks[2] = 65; // Initializing First array elements at position 2
Second Approach to create an Array in Java
In this approach, We will initialize the array at the declaration time only
int[] anIntegerArray = {15, 25, 35, 45, 55}
Here, We did not mention the array size but the compiler is intelligent enough to calculate the size by checking the number of elements.
Third Approach
Although this approach works without any error but, this is not the preferred way to initialize a java array
int Employees[ ] = {1, 2, 3, 4, 5}
Fourth Approach
Above 3 approaches are good to store small number of elements into an array, What if we want to store 50, 100 or more values. It will be a nightmare to add all of them using any of the above mentioned approaches. To resolve this, we can use the loop concept to store data into java array here:
int i, Employees[100];
for (i =0; i < 100 ; i++)
{
Employees[i] = i * 2;
}TIP: In order to store the elements in an array, We can use For loop, While Loop and Do While Loop
Fifth Approach of creating an array in Java
int[] anIntegerArray = new int[5];
anIntegerArray[0] = 10;
anIntegerArray[1] = 20;
anIntegerArray[2] = 30;
Here we declared an anIntegerArray array of size 5 but we only assigned 3 values to it. In this situation, the remaining values will be assigned to default values (0 in this case).
The above array will be:
//It means anIntegerArray[0] = 10 anIntegerArray[1] = 20 anIntegerArray[2] = 30 anIntegerArray[3] = 0 anIntegerArray[4] = 0
Accessing Java Array Elements
We can use the index position to access the elements of an Array in Java. Using index we can access or alter/change each and every individual element present in an array. Index value starts at 0 and end at n-1 where n is the size of an array (or Length of an array).
For example, if an array in Java stores 10 elements, index starts at 0 and ends at 9. To access or alter 1st value use Array_Name[0] and to access or alter 10th value, use Array_Name[10]. Lets see the example for better understanding of accessing Java array elements:
JAVA CODE
// Accessing Java Array elements example
package ArrayDefinitions;
public class ArrayTest {
public static void main(String[] args) {
int[] anIntegerArray = {15, 25, 35, 45, 55, 65};
System.out.println(anIntegerArray[0]);
System.out.println(anIntegerArray[1]);
System.out.println(anIntegerArray[2]);
System.out.println(anIntegerArray[3]);
System.out.println(anIntegerArray[4]);
System.out.println(anIntegerArray[5]);
}
}OUTPUT
Java Array example
In this Java array program, We will declare an integer array of size 10 and then we will sum those 10 values and displays the output.
// Java Array example: Sum of the elements inside an Array
package ArrayDefinitions;
public class JavaArray {
public static void main(String[] args) {
int i, Sum =0;
int [] anIntegerArray = {10, 20, 30, 40, 50, 60, 70, 80, 90, 100};
for(i = 0; i < anIntegerArray.length; i++) {
Sum = Sum + anIntegerArray[i];
System.out.format("Addition of %d to Sum = %d \n", anIntegerArray[i], Sum);
}
System.out.format("Sum of the elemts in anIntegerArray = %d \n", Sum);
}
}OUTPUT
ANALYSIS
In this Java array example Program, We declared 1 One Dimensional Arrays anIntegerArray[] with 10 elements and also declared i to iterate the Array elements,
int [] anIntegerArray = {10, 20, 30, 40, 50, 60, 70, 80, 90, 100};Below For loop will help to iterate each and every cell present in the anIntegerArray[4] array. Condition inside the for loops (i < anIntegerArray.length) will ensure the compiler, not to exceed the array limit.
- Sum = Sum + anIntegerArray[i]; statement is used to add each and individual array element present in the anIntegerArray to Sum variable.
- System.out.format statement will display the Sum value after every iteration.
TIP: anIntegerArray.length is used to find the length of an array.
for(i = 0; i < anIntegerArray.length; i++) {
Sum = Sum + anIntegerArray[i];
System.out.format("Addition of %d to Sum = %d \n", anIntegerArray[i], Sum);Let us see the Java array in a Iteration wise,
Java Array First Iteration
The value of i will be 0 and the condition (i < 10) is True. So, it will start executing the statements inside the loop.
Sum = Sum + anIntegerArray[i]
=> Sum + anIntegerArray[0]
Sum = 0 + 10 = 10
The value of i will be incremented by 1
Second Iteration
The value of i is 1 and the condition (1 < 10) is True. So, it will start executing the statements inside the loop
Sum = Sum + anIntegerArray[1]
Sum = 10 + 20 = 30
Third Iteration
After the increment, the value of i is 2 and the condition (2 < 10) is True. So, it will start executing the statements inside the loop
Sum += anIntegerArray[2]
=> 30 + 30 = 60
Fourth Iteration
The value of i is 3 and the condition (3 < 5) is True.
Sum = Sum + anIntegerArray[3]
Sum = 60 + 40 = 100
Fifth Iteration
The value of i is 4 and the condition (4 < 10) is True.
Sum = Sum +anIntegerArray[4]
=> 100 + 50 = 150
Sixth Iteration
The value of i is 5 and the condition (5 < 10) is True.
Sum += anIntegerArray[5]
Sum = 150 + 60 = 210
Seventh Iteration
After increment, i is 6 and the condition (6 < 10) is True.
Sum = Sum + anIntegerArray[6] => 210 + 70 = 280
Eighth Iteration
The value of i is 7 and the condition (7 < 10) is True.
Sum = Sum + anIntegerArray[7] => 280 + 80 = 360
9th Iteration
i is 8 and the condition (8 < 10) is True.
Sum = Sum + anIntegerArray[8]
=> 360 + 90 = 450
Value of i will be incremented by 1
10th Iteration
i is 9 and the condition (9 < 10) is True.
Sum = Sum + anIntegerArray[9]
Sum = 450 + 100 = 550
11th Iteration
The value of i is 10 and the condition (10 < 10) is Flase. So, it will exit from the for loop
Lastly, we used System.out.format statement to display the Sum
System.out.format("Sum of the elements in anIntegerArray = %d \n", Sum);