Find the Longest Substring in the given String Without Repetition of characters

Given a string, find the longest substrings without repeating characters. Iterate through the given string, find the longest maximum substrings.
package Logs;
import java.util.HashSet;
import java.util.Set;

public class longestsubstring {

private Set<String> subStrList = new HashSet<String>();
private int finalSubStrSize = 0;

public Set<String> getLongestSubstr(String input){
//reset instance variables
subStrList.clear();
finalSubStrSize = 0;
// have a boolean flag on each character ascii value
boolean[] flag = new boolean[256];
int j = 0;
char[] inputCharArr = input.toCharArray();
for (int i = 0; i < inputCharArr.length; i++) {
char c = inputCharArr[i];
if (flag[c]) {
extractSubString(inputCharArr,j,i);
for (int k = j; k < i; k++) {
if (inputCharArr[k] == c) {
j = k + 1;
break;
}
flag[inputCharArr[k]] = false;
}
} else {
flag[c] = true;
}
}
extractSubString(inputCharArr,j,inputCharArr.length);
return subStrList;
}

private String extractSubString(char[] inputArr, int start, int end){

StringBuilder sb = new StringBuilder();
for(int i=start;i<end;i++){
sb.append(inputArr[i]);
}
String subStr = sb.toString();
if(subStr.length() > finalSubStrSize){
finalSubStrSize = subStr.length();
subStrList.clear();
subStrList.add(subStr);
} else if(subStr.length() == finalSubStrSize){
subStrList.add(subStr);
}

return sb.toString();
}

public static void main(String a[]){
longestsubstring mls = new longestsubstring();
System.out.println(mls.getLongestSubstr("automation_tester"));
System.out.println(mls.getLongestSubstr("Selenium_Webdriver_is_AutomationTesting"));
System.out.println(mls.getLongestSubstr("sdsjk_uippj_agjhs_7890"));
System.out.println(mls.getLongestSubstr("abcabcbb"));
}
}


OutPut:
[ion_tes, mation_]
[nium_Webdr, um_Webdriv]
[agjhs_7890]
[cab, abc, bca]

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