Here is a Java program that demonstrates how to find the largest number in an array:

**
class ArrayLargestNumber
{
public int findLargest(int[] arr, int n) {
int largest = Integer.MIN_VALUE;
for (int i = 0; i < n; i++) {
if (arr[i] > largest) {
largest = arr[i];
}
}
return largest;
}
}
public class Main {
public static void main(String[] args) {
ArrayLargestNumber aln=new ArrayLargestNumber();
int[] arr = {1, 14, 2, 16, 10, 20, 5};
int n = arr.length;
int largest =aln.findLargest(arr, n);
System.out.println("Largest element is " + largest);
}
}
**

In this program, The findLargest method takes two arguments; the array, and the length of the array.

It then initialize the largest variable with the minimum possible integer value (Integer.MIN_VALUE).

The method then loops through the array, comparing each element with largest. If an element is greater than largest, the largest is updated.

At the end, largest will hold the largest element of the array.

This approach is simple and efficient in terms of time complexity as it goes through the array once and the time complexity is O(n)

Another way to find largest number is by using the inbuilt Arrays.sort(arr) method and return the last element of the array, since after sorting the last element is the largest.

Also, you could use the inbuilt Arrays.sort(arr, Comparator.reverseOrder()) to sort the array in descending order and get the 1st element which is the largest element.