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Java find difference between characters in StringBuffer

I'm working on an Anagram program and I'm currently working on a method called diff which should return a StringBuffer containing the chars that are in the first StringBuffer but not in the second one. So for example if the StringBuffers are abba and acca, then my diff method should return bb. So far I currently have loop with an if statement but it's not working. Any help would be appreciated. Thanks
public StringBuffer diff(){
StringBuffer diffVal = null;
for (int i =0; i < sBuffer1.length(); i++){
String let1 = String.valueOf(sBuffer1);
if (sBuffer2.indexOf(let1) == -1 ){
}
}
return diffVal;

I think you are trying to use a loop to examine one character by one character in sBuffer1. But String let1 = String.valueOf(sBuffer1); gives you the entire string of sBuffer1.
What you need is String let1 = sBuffer1.substring(i, i + 1) to take a single character from sBuffer1 to check if it exists in sBuffer2.
For example:
public static StringBuffer diff(StringBuffer sBuffer1, StringBuffer sBuffer2) {
StringBuffer diffVal = new StringBuffer();
for (int i = 0; i < sBuffer1.length(); i++) {
String let1 = sBuffer1.substring(i, i + 1); // get the character from sBuffer1
if (sBuffer2.indexOf(let1) == -1) {
diffVal.append(let1); // append the character to the diff
}
}
return diffVal;
}

ok this might work, your logic was a little bit wrong, this code is straight forward. search for the character if it doesn't exist in the second string buffer add it to the result SF.
public StringBuffer diff(){
StringBuffer diffVal = new StringBuffer();//initialize before you use it.
for (int i =0; i < sBuffer1.length(); i++){
String let1 = String.valueOf(sBuffer1.charAt(i))//get the character at the ith position.
if (sBuffer2.indexOf(let1) == -1 ){
diffVal.append(let1);
}
}
return diffVal;
}

Try this.
StringBuilder diffVal= new StringBuilder();
StringBuffer sBuffer1 = new StringBuffer("abbad");//input 1
StringBuffer sBuffer2 = new StringBuffer("acca");//input 2, you can ignore if you have already passed/defined these
for (int i =0; i < sBuffer1.length(); i++){
if(i >= sBuffer2.length()){//handles difference in input string length
diffVal.append(sBuffer1.substring(i, sBuffer1.length()));
break;
}
if (sBuffer1.charAt(i) != sBuffer2.charAt(i)) {
diffVal.append(sBuffer1.charAt(i));
}
}
System.out.println(diffVal);// I am printing it here
the out put is : bbd
One recommendation here is use StringBuilder if you the strings you are using here are not required to be synchronized

How to print String buffer lines from last to first order

I have requirement to print String buffer lines as last to first order.
Example :toString of Stringbuffer method is printing below output:
this
is
some
text
Desired output:
text
some
is
this

What you could do is to create an array, iterate over it.
String s = new String("this\nis\nsome\ntext");
String []tokens = s.split("\n");
for(int i = tokens.length - 1; i >= 0; --i)
System.out.println(tokens[i]);
StringBuffer s = new StringBuffer("this\nis\nsome\ntext");
String []tokens = s.toString().split("\n");
for(int i = tokens.length - 1; i >= 0; --i)
System.out.println(tokens[i]);
A better memory less approach would be.
StringBuffer s = new StringBuffer("this\nis\nsome\ntext");
String word = "";
for(int i = s.length() - 1; i >= 0; --i)
{
if(s.charAt(i) != '\n')
{
word = s.charAt(i) + word;
}
else{
System.out.println(word);
word = "";
}
}
if(!word.equals(""))
System.out.println(word);

StringBuffer is a final class so you cannot extend it and override its toString() method to achieve what you want to do. You will have to handle it in your code.
you will have to do something like this :
public class Reverse {
public static void main(String[] args) {
// TODO Auto-generated method stub
StringBuffer s =new StringBuffer();
s.append("this\nis\nsome\ntext");
String[] rev = s.toString().split("\n");
for(int i=rev.length-1;i>=0;i--) {
System.out.println(rev[i]);
}
}
}
o/p :
text
some
is
this
Hope that helps

StringBuffer does not, by itself, have the capacity to return the lines the way you want them. You can either get the whole string from the buffer and use string.split("\n") to split it into an array, which you can then iterate over back to front, or create a class of your own that provides a function that handles such an operation

This should probably do it:
String[] lines = myStringBuffer.toString().split(System.lineSeparator()); //or use any other character for splitting
for(int i=lines.length; i>0; i--) {
System.out.println(lines[i-1]);
}

StringBuffer or String also has a lastIndexOf.
StringBuffer buf = new StringBuffer("this\nis\nsome\ntext");
final String EOL = "\n"; // Or "\r\n" or even "\u0085".
for (int pos = buf.length(); pos > 0; ) {
int before = buf.lastIndexOf(EOL, pos);
before = before == -1 ? 0 : before + EOL.length();
String line = buf.substring(before, pos);
System.out.println(buf);
pos = before - EOL.length();
}
Note: StringBuilder is better.

Change a certain occurrence of a letter in a string

Say I have a string, and I want to change the second "a" in that string to an "e".
String elephant = "elaphant";
I tried using String.replace(), but that replaces all the a's in the string, returning "elephent".
elephant.replace("a", "e");
Is there any loop or method I can use to accomplish this? Thank you all.

You could convert it to a char array, switch out the desired letter, then convert it back to String?
String elephant = "elaphant";
int index = -1;
int count = 0;
while(count < 2) {
index = elephant.indexOf("a", index+1);
count++;
}
if(index >= 0 && index < elephant.length()) {
char[] tmp = elephant.toCharArray();
tmp[index] = "e";
elephant = new String(tmp);
}
Or if you prefer StringBuilder
StringBuilder sbTemp = new StringBuilder(elephant);
sbTmp = sbTmp.replace(index, index+1, "e");
elephant = sbTmp.toString();

You need to get the index of the first occurrence of a letter.
Try using the indexOf method.
int myIndex = elephant.indexOf('a');
Once you have the index, use StringBuilder to replace the value. Something like:
StringBuilder sb = new StringBuilder(elephant);
sb[index] = myIndex;
elephant = sb.ToString();

Code:
String elephant = "elaphant";
//convert the string to array of string
String[] sp = elephant.split("");
int countA = 0;
boolean seenTwice = false;
String result = "";
for (int i = 0; i < sp.length; i++) {
//count number of times that a has been seen
if (sp[i].equals("a")) {
countA++;
}
// if a has been seen twice and flag seenTwice has not been see
if (countA == 2 && !seenTwice) {
result += "e";
seenTwice = true;
} else {
result += sp[i];
}
}
System.out.println(result);
Output:
elaphent

Can anybody help me to correct the following code?

Please help me to identify my mistakes in this code. I am new to Java. Excuse me if I have done any mistake. This is one of codingbat java questions. I am getting Timed Out error message for some inputs like "xxxyakyyyakzzz". For some inputs like "yakpak" and "pakyak" this code is working fine.
Question:
Suppose the string "yak" is unlucky. Given a string, return a version where all the "yak" are removed, but the "a" can be any char. The "yak" strings will not overlap.
public String stringYak(String str) {
String result = "";
int yakIndex = str.indexOf("yak");
if (yakIndex == -1)
return str; //there is no yak
//there is at least one yak
//if there are yaks store their indexes in the arraylist
ArrayList<Integer> yakArray = new ArrayList<Integer>();
int length = str.length();
yakIndex = 0;
while (yakIndex < length - 3) {
yakIndex = str.indexOf("yak", yakIndex);
yakArray.add(yakIndex);
yakIndex += 3;
}//all the yak indexes are stored in the arraylist
//iterate through the arraylist. skip the yaks and get non-yak substrings
for(int i = 0; i < length; i++) {
if (yakArray.contains(i))
i = i + 2;
else
result = result + str.charAt(i);
}
return result;
}

Shouldn't you be looking for any three character sequence starting with a 'y' and ending with a 'k'? Like so?
public static String stringYak(String str) {
char[] chars = (str != null) ? str.toCharArray()
: new char[] {};
StringBuilder sb = new StringBuilder();
for (int i = 0; i < chars.length; i++) {
if (chars[i] == 'y' && chars[i + 2] == 'k') { // if we have 'y' and two away is 'k'
// then it's unlucky...
i += 2;
continue; //skip the statement sb.append
} //do not append any pattern like y1k or yak etc
sb.append(chars[i]);
}
return sb.toString();
}
public static void main(String[] args) {
System.out.println(stringYak("1yik2yak3yuk4")); // Remove the "unlucky" strings
// The result will be 1234.
}

It looks like your programming assignment. You need to use regular expressions.
Look at http://www.vogella.com/articles/JavaRegularExpressions/article.html#regex for more information.
Remember, that you can not use contains. Your code maybe something like
result = str.removeall("y\wk")

you can try this
public static String stringYak(String str) {
for (int i = 0; i < str.length(); i++) {
if(str.charAt(i)=='y'){
str=str.replace("yak", "");
}
}
return str;
}

Java: how do icheck if a certain character is within a string, then print out the position it is in relative to the string?

What I am trying to do, is create a method, that has a string and a character as parameters, the method then takes the string and searches for the given character. If the string contains that character, it returns an array of integers of where the character showed up. Here is what I have so far:
public class Sheet {
public static void main(String[] args) {
String string = "bbnnbb";
String complete = null;
//*******
for(int i = 0; i < string.length(); i++){
complete = StringSearch(string,'n').toString();
}
//********
}
public static int[] StringSearch(String string, char lookfor) {
int[]num = new int[string.length()];
for(int i = 0; i < num.length; i++){
if(string.charAt(i)== lookfor){
num[i] = i;
}
}
return num;
}
}
The method works fine, and returns this:
0
0
2
3
0
0
What I am trying to do, is make those into 1 string so it would look like this "002300".
Is there any possible way of doing this? I have tried to do it in the starred area of the code, but I have had no success.

just do
StringBuffer strBuff = new StringBuffer();
for(int i = 0; i<str.length(); i++)
{
if(str.charAt(i) == reqChar)
{
strBuff.append(str.charAt(i));
}
else
{
strBuff.append('0');
}
}
return str.toString();

Just add the result to the existing string with the += operator
String complete = "";
for(...)
complete += StringSearch(string,'n').toString();

I would just use java's regex library, that way it's more flexible (eg if you want to look for more than just a single character). Plus it's highly optimized.
StringBuilder positions = "";
Pattern pattern = Pattern.compile(string);
Matcher matcher = pattern.matcher(lookfor);
while(matcher.find()){
positions.append(matcher.start());
}
return positions;

Updated with StringBuilder for better practices.
public static String StringSearch(String string, char lookfor) {
StringBuilder sb = new StringBuilder();
for(int i = 0; i < string.length; i++){
if(string.charAt(i) == lookfor)
sb.append(i);
else
sb.append("0");
}
return sb.toString();
}
Then you can just call it once, without a for loop. Not sure why you call it for every character in the string.
complete = StringSearch(string,'n');