Java is clearly a pass by value but wanted some clarification

I don't know any languages which are pass-by-reference all the time, but C# has the ref modifier which allows a specific parameter to use pass-by-reference. That allows you to see the difference pretty easily. For example:

using System;

public class Program
{
    static void Main()
    {
        string x = "original x";
        string y = "original y";
        Modify(x, ref y);
        Console.WriteLine(x);
        Console.WriteLine(y);
    }

    static void Modify(string px, ref string py)
    {
        px = "modified x";
        py = "modified y";
    }
}

The output is

original x
modified y

That's because the assignment to px doesn't affect x in the calling code: the value of x was passed to the method. But the assignment to py does change y, because y was passed by reference; py and y are aliases for the same storage location, basically.

All of this only matters when you modify the parameters themselves. Compare the above program with this one:

using System;
using System.Text;

public class Program
{
    static void Main()
    {
        StringBuilder x = new StringBuilder("original x");
        Modify(x);
        Console.WriteLine(x);
    }

    static void Modify(StringBuilder px)
    {
        px.Length = 0;
        px.Append("modified x");
    }
}

Now the Modify method doesn't change the value of px at all - instead of makes changes to the object that the value of px refers to. No pass-by-reference is required - the value of x is passed to the method by value, and that is copied into px. This is like copying your home address on a piece of paper and giving it to someone. It's not copying the house itself - it's just copying the way of reaching the house. If the person you've given the paper to goes and paints the front door red, then when you go home you'll see that change.

This is why it's important to understand the difference between variables, objects and references.