Nested Recursion Error

Question

public static void main(String[] args) {
    PrintAsteriskLine(5);
    System.out.println("Separate");
    PrintAsterisk(7);
}

public static void PrintAsterisk(int N)
{
    if (N==1)
        PrintAsteriskLine(N);
    else
        PrintAsteriskLine(N);
        PrintAsterisk(N-1);  
}// end PrintAsterisk

public static void PrintAsteriskLine(int N)
{
    if (N==1)
            System.out.println("*");
    else
    {
        System.out.print("*");
        PrintAsteriskLine(N-1);
    }
} // end PrintAsteriskLine

Above is my code in Java. I'm coding on NetBeans. The idea was to nest the PrintAsteriskLine function inside the PrintAsterisk function to print N number of lines of asterisks, starting at N and incrementing towards 1. For an example, if I input 3 as an argument, then the following would be the output:

***
**
*

Now, my code does do that. However, it also gives me a stack overflow error that I don't understand. Can someone explain to me what is happening? Is it because I'm nesting recursive functions? I really am at a loss. It works but gives me an error message :/

Exception in thread "main" java.lang.StackOverflowError at sun.nio.cs.UTF_8$Encoder.encodeLoop(UTF_8.java:691) at java.nio.charset.CharsetEncoder.encode(CharsetEncoder.java:579) at sun.nio.cs.StreamEncoder.implWrite(StreamEncoder.java:271) at sun.nio.cs.StreamEncoder.write(StreamEncoder.java:125) at java.io.OutputStreamWriter.write(OutputStreamWriter.java:207) at java.io.BufferedWriter.flushBuffer(BufferedWriter.java:129) at java.io.PrintStream.write(PrintStream.java:526) at java.io.PrintStream.print(PrintStream.java:669) at madisonbrewerrecursion.MadisonBrewerRecursion.PrintAsteriskLine(MadisonBrewerRecursion.java:38)

Then it says

at madisonbrewerrecursion.MadisonBrewerRecursion.PrintAsteriskLine(MadisonBrewerRecursion.java:39)

A whole bunch of times. Line 38 is the print statement in PrintAsteriskLine and 39 is the clone-call/incrementation. So, as far as I can see it has a problem with my PrintAsteriskLine function, which works fine when called on its own, though.

thedayturns · Accepted Answer · 2015-09-19 18:38:16Z

2

It's an issue with your indentation. Look here

public static void PrintAsterisk(int N)
{
    if (N==1)
        PrintAsteriskLine(N);
    else
        PrintAsteriskLine(N);
        PrintAsterisk(N-1);  
}// end PrintAsterisk

You indented both things after the else as if you intended them both to happen if N != 1. However, since you didn't wrap them with curly braces, only the first line after the else will execute if N != 1. PrintAsterisk(N-1) will be run in both cases, so the recursion will never terminate.

You want to do something like this:

public static void PrintAsterisk(int N)
{
    if (N==1) {
        PrintAsteriskLine(N);
    } else {
        PrintAsteriskLine(N);
        PrintAsterisk(N-1);  
    }
}// end PrintAsterisk

answered Sep 19, 2015 at 18:38

thedayturns

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2 Comments

trashpanda Over a year ago

Lulz! The herpest of derps. Stupid Syntax, why can't it just magic its way through my buggy spaghetti? But thanks, though, I couldn't figure it out for the life of me... Man, that's sad...

async Over a year ago

Wow. It really does happen. @MadisonC.Brewer, I guess one way to prevent this is by always using braces, even for single-statement ifs and elses :P

sifho · Accepted Answer · 2015-09-19 19:03:37Z

0

Your code does not handle what happens when N<1 and for this reason the recursion never ends. Try this.

public static void PrintAsterisk(int N)
    {
        if(N<1)
            return;
        if (N==1)
            System.out.println("*");
        else
            PrintAsteriskLine(N);
            PrintAsterisk(N-1);  
    }// end PrintAsterisk

edited Sep 19, 2015 at 19:03

answered Sep 19, 2015 at 18:49

sifho

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