String.indexOf gives a value one less than expected

问题

I do not understand the behaviour of the String.index Of method.

String peter = "Peter Piper picked a peck of pickled pepper";
  System.out.println("The number of p in the sentence is, " + peter.indexOf('p')); 

Why is the output of p 8 and not 9? There are 9 P's in the sentence.

回答1:

Indexes are zero-based:

        ↓
Peter Piper picked a peck of pickled pepper
          111111111122222222223333333333444
0123456789012345678901234567890123456789012
        ↑

The first p is at index 8.

From the javadoc of indexOf():

Returns the index of the first occurrence of the character in the character sequence represented by this object, or -1 if the character does not occur.

来源：https://stackoverflow.com/questions/34214064/string-indexof-gives-a-value-one-less-than-expected