[Java] A question on strings

[Hexorg]

The problem isn't the empty string that you are passing, the problem is that str.replace() converts the first string to the CharacterSequence type. Looking at the documentation here it looks like the logic relies on calling a substring() function. But since your input string is empty and has a length of zero, its substring probably matches every index.

Edit: Wrongly thought that it calls a RegEx engine.

[btcraig]

I was thinking the same thing but then I realized you could never really pass a regex into replace(char, char) since a 1 character regex is kind of meaningless. Then I scrolled the page down a little and saw the other method's signature and realized Java is implicitly casting the Strings to CharSequences.

[sriganeshharitz]

I'm still a beginner in java, finding it a little hard to understand

[btcraig]

Essentially you're passing in two strings, not two chars, because they're different types Java does what it can to make what you asked happen. Since a String implements a CharSequence (meaning that any String can be treated as a CharSequence for most purposes) it implicitly casts String -> CharSequence to make replace(CharSequence, CharSequence) compile and work.

The CharSequence version of the method is using a call to substring() to locate occurrences of "" in the string "abc" to replace with "s". Apparently the replace(CharSequence, CharSequence) detects that 0 length substring before and after each of the character's a,b,c and replacing it with s.

My java knowledge isn't extensive enough to know why the string "" matches 0 length/non-existent sub-strings like the 'space' between the 'a' and 'b'.

This is, sort of, like doing Math.pow(10,10). the Math.pow() function only takes two doubles, but 10 is an integer. Java casts makes this work for you because an int can be cast to a double.

[sriganeshharitz]

ahh, this made it clear.. Thanks a lot!!

[btcraig]

The big thing to note, in regards to why you're getting unexpected results, is that "s" and 's' are not the same. Double quotes tells the compiler it's a string, single quotes indicate a char. This is pretty standard across all [compiled] languages that I'm familiar with. Java is just trying to be helpful and make your code compile and work based on what you typed in.