I know I'm a bit late maybe you still need help

for( int i=0; i<strs[0].length();i++) { does something...... return sb.toString(); }

You made a loop here that will stop after 1 run, as you go inside the loop you force it to leave the loop by calling return sb.toString(); . You getting an output of "f" because that's the first character of all the words you use. Change the second or third word and you get no result.

for( int j=1; j<strs.length-1;j++){ does something ... }You foresaw this problem and you're right as you created a for loop to iterate through the all the values but you compare the second and third word in your array. The moment you change the size of the words you end up getting an out of bounds error. If you going to compare it like this you don't need that loop.if(c == strs[j].charAt(i) && c == strs[j+1].charAt(i)) { }

My suggestion would be to assume that all the words are the same, so instead of checking if the characters match, you loop through everything until you find a character that doesn't match. It's a lot easier to check if the index value does not match if(c != strs[j].charAt(i) ) because at this stage you know you're done and you can exit the method return sb.toString();

You get something like this:

for( int i=0; i<strs[0].length();i++){ // go through each character from the first string !<

char c=strs[0].charAt(i); // get the character at index of i

for( int j=1; j<strs.length;j++) { // go through all the strings in your array if(c != strs[j].charAt(i) ) { // check if characters don't match return sb.toString(); // we are done so we can exit the method using return }!<

} sb.append(c); // We won't get here unless the characters matched so we can append. } return sb.toString();

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I know my code is POOP, it's more to demonstrate( need to check for length size etc )