Thread: Test Question(Introduction Course)

Hey guys,

Here is the question: Design Java code to find and return the frequency of string b in string a.

For example , if string a = "abcdabcfabxyabd" and string b = "ab"
The frequency should be equal to 4

Here is my code:

import java.util.*;
public class StringFrequency_A_in_B 
{
	 public static void main(String[] args) 
	    {
	    	Scanner scan = new Scanner(System.in);
	    	String s1, s2;
	    	String commonChars = "";
	    	int lengthCommon = 0;
 
                System.out.println("The program will find the characters " + "quantity/frequancy \nof the first string in the second string");
		System.out.println("Now, enter two strings in seperate lines");
 
		s1 = scan.nextLine(); 
		s2 = scan.nextLine();
 
		int len = s1.length(); // number of characters in string A
 
		for (int i = 1; i < len ; i++)
		{
		    char ch = s1.charAt(i);
		    if (s2.indexOf(ch) != -1)
		    {
		        commonChars = commonChars + ch;
		    }
		} // end of the loop
 
		lengthCommon = commonChars.length();
 
                System.out.println("The common characters: " + commonChars);
                System.out.println("The frequency of common characters: ” + lengthCommon);
 
		System.exit(0);
	    }
}

The thing is that it doesn't count the frequency of "ab", but the quantity of a's and b's, so it shows 8. How do I make it count frequency of "ab" string?

Don't look for common chars since char is not what you're interested in. Instead search for Strings within a String.

So I should use String instead of chars, right??

--- Update ---

I have changed my code and it shows the right answer, but the output shows like a few Errors before the answer:

Error
Error
Error
Error
Error
Error
4

import java.util.*;
public class FrequencyAinB 
{
	public static void main (String [] args)
	{
	Scanner scan = new Scanner(System.in);
	String a,b;
	int freq = 0;
	int pos;
	a = "abcdabcfabxyabd";
	b = "ab";
 
	int lenA = a.length() - 1;
 
	while(lenA>0)
	{	
		lenA--;
		pos = a.indexOf(b);
		if(pos == -1)
		{
			System.out.println("Error");
		}
		else
		{
			a = a.substring (pos + 1);
			freq++;
		}
	}
	System.out.println(freq);
	}
}

What's wrong with logic?

You're while loop looks quite a bit strange. Why are you dealing with a length variable, lenA? What's the point of that? Why are you creating a substring of the a String? Why not use one of the overrides of the indexOf method that takes a second parameter?