Array in Java

dataType[] arrayRefVar = new dataType[arraySize];

Alternatively you can create arrays as follows:

dataType[] arrayRefVar = {value0, value1, ..., value n};

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.

Processing Arrays:

When processing array elements, we often use either for loop or foreach loop because all of the elements in an array are of the same type and

the size of the array is known.

Example:

Here is a complete example of 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);

   }

}

Result: 

This would produce the following result:

1.9

2.9

3.4

3.5

Total is 11.7

Max is 3.5

(Enhanced for loop, which enables you to traverse the complete array sequentially without using an index variable.)

Passing Arrays to Methods:

Just as you can pass primitive type values to methods, you can also pass arrays to methods. For example, the following method displays the

elements in an int array:

public static void printArray(int[] array) {

  for (int i = 0; i < array.length; i++) {

    System.out.print(array[i] + " ");

  }

}

You can invoke it by passing an array.
For example, the following statement invokes the printArray method to display 3, 1, 2, 6, 4, and 2:

printArray(new int[]{3, 1, 2, 6, 4, 2});

Returning an Array from a Method:

A method may also return an array. For example, the method shown below returns an array that is the reversal of another array:

public static int[] reverse(int[] list) {

  int[] result = new int[list.length];

  for (int i = 0, j = result.length - 1; i < list.length; i++, j--) {

    result[j] = list[i];

  }

  return result;

}

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

1-public static int binarySearch(Object[] a, Object key)
Searches the specified array of Object ( Byte, Int , double, etc.) for the specified value using the binary search algorithm. The array must be

sorted prior to making this call. This returns index of the search key, if it is contained in the list; otherwise, (-(insertion point + 1).

2- public static boolean equals(long[] a, long[] a2)

Returns true if the two specified arrays of longs are equal to one another. Two arrays are considered equal if both arrays contain the same

number of elements, and all corresponding pairs of elements in the two arrays are equal. This returns true if the two arrays are equal. Same

method could be used by all other primitive data types (Byte, short, Int, etc.)

3- public static void fill(int[] a, int val)

Assigns the specified int value to each element of the specified array of ints. Same method could be used by all other primitive data types

(Byte, short, Int etc.)

4-public static void sort(Object[] a)

Sorts the specified array of objects into ascending order, according to the natural ordering of its elements. Same method could be used by all

other primitive data types ( Byte, short, Int, etc.)