Accept Array Of Non-negative Integers And Return Second Largest Integer

Write a function that accepts an array of non-negative integers and returns the second largest integer in the array.

Return -1 if there is no second largest.

The signature of the function is int f(int[ ] a)

Examples:

if the input array isreturn{1, 2, 3, 4}3{{4, 1, 2, 3}}3{1, 1, 2, 2}1{1, 1}-1{1}-1{}-1 

In the signature what I understood is, I should write my function with the given signature,

The return type is "int"

method name is "f"

parameter is "a" right ?
 
Writing my doubts beside the particular line in the code

public static void main()  // In the answer why they didn't use the class ?

In main method why they didn't use parameters ?(String[] args)

{
a1(new int[]{1, 2, 3, 4}); // what is "a1" here is it array name ? this line initializing the array ?
a1(new int[]{4, 1, 2, 3});
a1(new int[]{1, 1, 2, 2});
a1(new int[]{1, 1});
a1(new int[]{1});
a1(new int[]{});
} 

static int a1(int[] a) // what is "a" here parameter ? and "a1" is method name ? why they used the array name and method name same ?

{
int max1 = -1;
int max2 = -1;
for (int i=0; i<a.length; i++)

[Code] .....