javastringstring-matching

Find the Number of Occurrences of a Substring in a String

Why is the following algorithm not halting for me?

In the code below, str is the string I am searching in, and findStr is the string occurrences of which I'm trying to find.

String str = "helloslkhellodjladfjhello";
String findStr = "hello";
int lastIndex = 0;
int count = 0;
    
while (lastIndex != -1) {
    lastIndex = str.indexOf(findStr,lastIndex);
    
    if( lastIndex != -1)
        count++;
           
    lastIndex += findStr.length();
}

System.out.println(count);
Solution

  • The last line was creating a problem. lastIndex would never be at -1, so there would be an infinite loop. This can be fixed by moving the last line of code into the if block.

    String str = "helloslkhellodjladfjhello";
String findStr = "hello";
int lastIndex = 0;
int count = 0;

while(lastIndex != -1){

    lastIndex = str.indexOf(findStr,lastIndex);

    if(lastIndex != -1){
        count ++;
        lastIndex += findStr.length();
    }
}
System.out.println(count);