OnMouseOver GUI not appearing

Questions & Answers
1 
objRect.y = Mathf.Abs(MousePos.y - Camera.main.pixelHeight);

Is there a Java equivalent to C#'s Mathf.Abs?

Thank you.

EDIT: This is my complete script, I have another problem!

var ShowRollover;
var objRect : Rect;
var mousePos : Vector2;
var offset : Vector3;

offset = new Vector3(16, 16, 0);

function Update()
{
    ShowRollover = false;
    objRect = new Rect(0, 0, 500, 100);
    mousePos = new Vector2(0, 0);
}

function OnMouseOver()
{
    ShowRollover = true;
}

function OnMouseExit()
{
    ShowRollover = false;
}

function OnGUI()
{
    if (ShowRollover)
    {
        mousePos = Input.mousePosition + offset;
        objRect.x = mousePos.x;

        GUI.contentColor = Color.yellow;

        objRect.y = Mathf.Abs(mousePos.y - Camera.main.pixelHeight);    
        GUI.Label(objRect, "Name: Common Carp
Number of fish in patch: 8");
    }
}

I found that if the label cannot be seen even when I'm hovering the mouse over the object with the collider. Is there any mistake that I made?

2

Mathf.Abs isn't C#, it's a Unity-specific function (Mathf is a Unity-specific class). System.Math.Abs isn't C# either, it's Mono/.NET. In fact there are no functions that are C#-only. The code you wrote is valid JS. (However Java is not a valid "nickname" for Javascript, as it's a different language entirely, and not used in Unity.)