java split with unknown result

Question

for the following code,

1. why there is empty string in position 2,3,5,6,8?

2. then why "b", ":andf", "1" has no empty string behind?

    String[] splitStrs = "booo:and:fooo1o".split("o", -1);  
    System.out.println(splitStrs.length);  
    for (int i=0; i<splitStrs.length; i++) {  
        System.out.println("\"" + splitStrs[i]+ "\"");  
    }

output is:

8
"b"
""
""
":and:f"
""
""
"1"
""

Answer 1

why there is empty string in position 2,3,5,6,8?

When splitting on "o", there's nothing between the o's in "ooo", thus empty strings.

then why "b", ":andf", "1" has no empty string behind?

But there is an empty string at the end of your output, i.e., behind "1".

Per the documentation, a negative 2nd arg specifically means "trailing empty strings not discarded".

Always read the doc.

Answer 2

The split method will find all occurances where is wanted character (in your example "o"), put a new (sub)string between current "o" and next "o", without the "o" character, in array, and continue for the whole string.

When you have, for an example "oo", it will be "" since there is nothing between those 2 "o" characters.

Let's take an example. You have a string "Oh, hello Anna! I havent seen you since 2010s!" and split this string on every place where is "a" character.

First, start from the first character, then find where is next letter "a", which is found on 14th index. Take part of the string from start to that place where is "a" and add it into an array. First element of an array will look like "Oh, hello Ann" ("A" and "a" are different characters). Then start from that "a" where I have found (14th index) and find next "a" , which is in 20th index in our example. Take part of the string from first and second "a" and copy it in an array. Then the procedure goes on until the end of the string.

Result will be:

"Oh, hello Ann"
"! I h"
"vent seen you since 2010s!"

If we split our same string on every "n", by using same logic, we will get:

"Oh, hello A"
""
"a! I have"
"t see"
" you si"
"ce 2010s"

Reason why I get an empty string on second part is because in "...Anna...", there is nothing between those 2 "n" characters

Some examples can be found on: https://www.geeksforgeeks.org/split-string-java-examples/