Error: symbol not found

Error message
StringTest_2.java:25: error : No symbols found
while((index=indexOf(key))!=-1)
^
Symbol : Method indexof(String)
Location : class StringTest_2
1 A mistake

The code is as follows

public class StringTest_2
{
    
	public static void main(String[] args)
	{
    
		String str="abcbjfbeabcjefjabcjepofkjabcniabc";
		String key="abc";
		int count=getKeyStringCount(str,key);
		System.out.println("count="+count);
	}
	public static int getKeyStringCount(String str,String key)
	{
    
		// Define counters 
		int count=0;
		// Define variable records key Position of appearance 
		int index=0;
		while((index=indexOf(key))!=-1)
			{
    
				str=str.substring(index+key.length());
				count++;
			}
		return count;
	}
}

   Common symbols that cannot be found are matching errors or undefined symbols , I checked the symbols and found no errors , Tried the guide bag again , All useless .
   Found behind while((index=indexOf(key))!=-1) In a sentence indexOf(key) of no avail str Object call ,int indexOf(String str) The function of is to return the first occurrence of the specified string in the index of the string , Without calling the string object, its function cannot be realized ！

resolvent
   So it's going to be while((index=indexOf(key))!=-1)
   Change to while((index=str.indexOf(key))!=-1)