Java – Arrays
Java provides a data structure, the array, which stores a fixed-size sequential collection of elements of the same type. An array is used to store a collection of data, but it is often more useful to think of an array as a collection of variables of the same type.
Instead of declaring individual variables, such as number0, number1, ..., and number99, you declare one array variable such as numbers and use numbers[0], numbers[1], and ..., numbers[99] to represent individual variables.
This tutorial introduces how to declare array variables, create arrays, and process arrays using indexed variables.
Declaring Array Variables
To use an array in a program, you must declare a variable to reference the array, and you must specify the type of array the variable can reference. Here is the syntax for declaring an array variable −
Syntax
dataType[] arrayRefVar; // preferred way.
or
dataType arrayRefVar[]; // works but not preferred way.
Note − The style dataType[] arrayRefVar is preferred. The style dataType arrayRefVar[] comes from the C/C++ language and was adopted in Java to accommodate C/C++ programmers.
The following code snippets are examples of this syntax −
double[] myList; // preferred way.
or
double myList[]; // works but not preferred way.
Creating Arrays
Syntax
arrayRefVar = new dataType[arraySize];
The above statement does two things −
It creates an array using new dataType[arraySize].
It assigns the reference of the newly created array to the variable arrayRefVar.
Declaring an array variable, creating an array, and assigning the reference of the array to the variable can be combined in one statement, as shown below −
dataType[] arrayRefVar = new dataType[arraySize];
Alternatively you can create arrays as follows −
dataType[] arrayRefVar = {value0, value1, ..., valuek};
The array elements are accessed through the index. Array indices are 0-based; that is, they start from 0 to arrayRefVar.length-1.
Example
Following statement declares an array variable, myList, creates an array of 10 elements of double type and assigns its reference to myList −
double[] myList = new double[10];
Following picture represents array myList. Here, myList holds ten double values and the indices are from 0 to 9.
Arrays in Java|Introduction to Arrays in Java
Example
Here is a complete example showing how to create, initialize, and process arrays
public class TestArray {
public static void main(String[] args) {
double[] myList = {1.9, 2.9, 3.4, 3.5};
// Print all the array elements
for (int i = 0; i < myList.length; i++) {
System.out.println(myList[i] + " ");
}
// Summing all elements
double total = 0;
for (int i = 0; i < myList.length; i++) {
total += myList[i];
}
System.out.println("Total is " + total);
// Finding the largest element
double max = myList[0];
for (int i = 1; i < myList.length; i++) {
if (myList[i] > max) max = myList[i];
}
System.out.println("Max is " + max);
}
}
Output
1.9
2.9
3.4
3.5
Total is 11.7
Max is 3.5
The foreach Loops
JDK 1.5 introduced a new for loop known as foreach loop or enhanced for loop, which enables you to traverse the complete array sequentially without using an index variable.
Example
public class TestArray {
public static void main(String[] args) {
double[] myList = {1.9, 2.9, 3.4, 3.5};
// Print all the array elements
for (double element: myList) {
System.out.println(element);
}
}
}
Output
1.9
2.9
3.4
3.5
Multi-Dimensional Array
A multi-dimensional array is very much similar to a single dimensional array. It can have multiple rows and multiple columns unlike single dimensional array, which can have only one full row or one full column.
Array Declaration
Syntax:
datatype[ ][ ] identifier;
or
datatype identifier[ ][ ];
Initialization of Array
new operator is used to initialize an array.
Example:
int[ ][ ] arr = new int[10][10]; //10 by 10 is the size of array.
or
int[ ][ ] arr = {{1,2,3,4,5},{6,7,8,9,10},{11,12,13,14,15}};
// 3 by 5 is the size of the array.
Accessing array element
For both, row and column, the index begins from 0.
Syntax:
array_name[m-1][n-1]
Example:
int arr[ ][ ] = {{1,2,3,4,5},{6,7,8,9,10},{11,12,13,14,15}};
System.out.println("Element at (2,3) place" + arr[1][2]);
Two Dimensional Arrays in Java|2D Arrays in Java|
Jagged Array
Jagged means to have an uneven edge or surface. In java, a jagged array means to have a multi-dimensional array with uneven size of rows in it.
Initialization of Jagged Array
new operator is used to initialize an array.
Example:
int[ ][ ] arr = new int[3][ ]; //there will be 10 arrays whose size is variable
arr[0] = new int[3];
arr[1] = new int[4];
arr[2] = new int[5];
The Arrays Class
The java.util.Arrays class contains various static methods for sorting and searching arrays, comparing arrays, and filling array elements. These methods are overloaded for all primitive types.
Type Casting
Assigning a value of one type to a variable of another type is known as Type Casting.
In Java, type casting is classified into two types,
Widening Casting(Implicit)
Narrowing Casting(Explicitly done)
Widening or Automatic type converion
Automatic Type casting take place when,
the two types are compatible
the target type is larger than the source type
Example :
public class CastTest1
{
public static void main(String[] args)
{
int i = 100;
long l = i; //no explicit type casting required
float f = l; //no explicit type casting required
System.out.println("Int value "+i);
System.out.println("Long value "+l);
System.out.println("Float value "+f);
}
}
Output :
Int value 100
Long value 100
Float value 100.0
Narrowing or Explicit type conversion
When you are assigning a larger type value to a variable of smaller type, then you need to perform explicit type casting.
Example :
public class CastTest2
{
public static void main(String[] args)
{
double d = 100.04;
long l = (long)d; //explicit type casting required
int i = (int)l; //explicit type casting required
System.out.println("Double value "+d);
System.out.println("Long value "+l);
System.out.println("Int value "+i);
}
}
Output :
Double value 100.04
Long value 100
Int value 100
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