Print an ASCII diamond
There are a few things that we can do to clean this up.


This is something I would extract to its own method.  Handle getting the user input in the main() method, and then pass that on to the drawDiamond() method.
Your for loops are divided into iterating over lines, spaces, and
marks.  We can simplify that down to just rows and columns where we can iterate over each individual unit at a time.  This will also eliminate one of your System.out.println()s in the final method.
We can simplify down the math of where to print a piece of the diamond.

if ((column == Math.abs(row - half)) || (column == (row + half)) || (column == (sqr - row + half - 1)))



Final Method:

void drawDiamond(int sqr)
{
    int half = sqr/2;
    for (int row=0; row&lt;sqr; row++)
    {
        for (int column=0; column&lt;sqr; column++)
        {
            if ((column == Math.abs(row - half)) || (column == (row + half)) || (column == (sqr - row + half - 1)))
            {
                System.out.print("*");
            }
            else System.out.print(" ");
        }
        System.out.println();
    }
}