class Generate//to print all numbers from 1000 to 9999 whose digits are in ascending order
{
    private boolean order(int n, int i)//checks if the digits of given number are in ascending order
    {
        if(n==0)
        return true;
        if(n<i)
        return(order(n/10,n));
        return false;
    }
    void show(int n)//recursive function to generate numbers from 1000 to 9999
    {
        if(n>9999)//base case for recursor
        System.out.print("");
        else
        {
            if(order(n,10))//if digits are in ascending order, prints the number
            System.out.println(n);
            show(n 1);//recursive call
        }
    }
}

The above code was supposed to print all numbers from 1000 to 9999. Code compiled and run but received a runtime exception: Java.lang.StackOverflowError: null. Would a try catch block fix my problem? This is my first time posting here hence I am not familiar with the question etiquette, please correct me if I'm wrong.

CodePudding user response：

Java (and most of the programming languages) provides finite number of memory slot to be used for stack-frame, when your program/code reaches that limit it throws the StackOverFlow error.

In your case, your program reaches that limit before coming to base condition.

My take on this -

1. Do not use Recursive approach until and unless you are splitting your problem into acceptable sub-problems.

2. this shows you how you can increase stack-frame-size to be used by the JVM for a particular thread.

CodePudding user response：

In my opinion StackOverFlow is due to double recursion i.e both show(), and order() are recursive... I think show() does not need to be recursive. modified your code as under:

 public static void main(String[] args) {
        /
        new Generate().show(); // added main function to get output or exception.. you can omit it and call Generate().show() at the point u require.
    }
}
    class  Generate//to print all numbers from 1000 to 9999 whose digits are in ascending order
{
    private boolean order(int n, int i)//checks if the digits of given number are in ascending order
    {
        if(n==0)
        return true;
        if(n<i)
        return(order(n/10,n));
        return false;
    }
    void show()//function to generate numbers from 1000 to 9999 - WITHOUT Recursion
    {
        int n = 1000;
        while(n<=9999)
        { if(order(n,10))//if digits are in ascending order, prints the number
            System.out.println(n);
            n  ;
        }
    }
}

and here is output: (showing first 7 iterations only) 1234 1235 1236 1237 1238 1239 1245 .......