How to find string within a string using for loop in java?

Question

I'm trying to find if user input s contains the second user input s1 using for loops and if statements. I only want to use methods .charAt() and .length and not .indexOf to find if s1 is within s. Once I find whether s contains s1 or not, I either want to return .charAt() where s1 begins in s, or return -1 if s1 doesn't occur at all inside s.

For example, s = abcdefghi & s1 = def, it will return 3.

This is my code so far: It either returns 0 or -1

package javaapplication5;

import java.util.Scanner;
class myStrings {
String s, s1;

void setMyStrings(String str, String str1) {
    s = str;
            s1 = str1;
}

int find() {
    int i, j;
    int r = -1;
    char ns = s1.charAt(0);
    int sp;
    int count = 1;

    for (i = 0; i < s.length(); i++){
        if (s.charAt(i) == ns) {
            sp = i;//starting point
            for (j = i+1; j < s1.length(); j++) {
                ns += 1;
                if (s.charAt(j) == ns){
                    j++;
                    count++;
                }
                if (count == s1.length())
                    r = sp;
            }
        }   
    }
    System.out.println(r);
    return r;
   }
}
public class JavaApplication5 {
public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    myStrings setS = new myStrings();

    String s, s1;

    System.out.print("Enter s:");
    s = in.nextLine();
    System.out.print("Enter s1:");
    s1 = in.nextLine();

    setS.setMyStrings(s1, s1);
    setS.find();

}

}

libik · Accepted Answer · 2013-10-30 23:37:16Z

1

:D, it is because this line in your main method

setS.setMyStrings(s1, s1);

You add the same value.

Also If I look good, this line

for (j = i+1; j < s1.length(); j++)

Should be written as this :

for (j = i+1; j < i+1+s1.length(); j++)

Also this line is wrong

ns += 1;

ns is char, it means, this for example change char A to B. You need something like this :

ns = s1.charAt(j-i)

edited Oct 30, 2013 at 23:37

answered Oct 30, 2013 at 23:31

libik

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Comments

Costi Ciudatu · Accepted Answer · 2013-10-30 23:33:27Z

0

So you're trying to implement String.indexOf(String) yourself.

A place to start (or a way to cheat, depending on what your goal is) would be to look at the actual JDK implementation in class String: it delegates to a package-private static method which does exactly what you're trying to do:

static int indexOf(char[] source, int sourceOffset, int sourceCount,
                   char[] target, int targetOffset, int targetCount,
                   int fromIndex) {
    // ...

answered Oct 30, 2013 at 23:33

Costi Ciudatu

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Comments

Tyco · Accepted Answer · 2013-10-30 23:34:31Z

0

Java isn't C, you cannot go to next char with

ns += 1;

You have to do something like:

if (s.charAt(j) == s1.charAt(j-sp)){

answered Oct 30, 2013 at 23:34

Tyco

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1 Comment

Tyco Over a year ago

Even in C, this will be wrong since you didn't reinitialize ns when inner loop fail to find the string.

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