Sum_Recursive.java

public class Sum_Recursive {
    private String sumString (final int n) {return "sum (" + n +")";}
    private int max = 0;
    private void printout (final int n, final String s) {
        System.out.println( sumString(n));
        for (int i = 0 ; i <= max - n; ++i) {System.out.print(" ");}
        System.out.print(s);
    }

    private int sum(final int n) {
        System.out.println("call" + sumString(n));
        if (n > max) {max = n;}
        if (n == 0) {
            printout(n, "n == 0, return 0\n");
            return 0;
        }

        else {
            printout(n, "n != 0,");
            final int x = sum (n - 1);
            printout(n, "return" + x + " + " + n + " (" + ( x + n) + ") \n ");
            return x + n;

        }
    }

    public static void main (final String [] args) {
        final Sum_Recursive obj = new Sum_Recursive();
        obj.sum(5);
    }
}