Java and regular expressions: Why do the two matches mean the same? -Php Tutorial

{Code...} matches hopeful. If yes, the hope in hopeful is captured. Of course, continue to search for matched substrings from f. The comparison shows that ,(? Hopeful) hope and hope (? Ful), the effects of the two regular expressions are the same, although the above descriptions are still...

javaPattern p = Pattern.compile("(?=hopeful)hope");  String str = "hopeful";  Matcher m = p.matcher(str);  while(m.find()){     System.out.println(m.group());  }

Whether it can match hopeful. if it can, the hope in hopeful is captured.

Of course, continue to search for matched substrings from f. The comparison shows that ,(? = Hopeful) hope and hope (? = Ful). The two regular expressions have the same effect.

Although I can't understand the above description, I only saw hope (? = Ful) how can I understand this writing method? I always thought (? =) Is used to match whether the form ends with xxx...

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javaPattern p = Pattern.compile("(?=hopeful)hope");  String str = "hopeful";  Matcher m = p.matcher(str);  while(m.find()){     System.out.println(m.group());  }

Whether it can match hopeful. if it can, the hope in hopeful is captured.

Of course, continue to search for matched substrings from f. The comparison shows that ,(? = Hopeful) hope and hope (? = Ful). The two regular expressions have the same effect.

Although I can't understand the above description, I only saw hope (? = Ful) how can I understand this writing method? I always thought (? =) Is used to match whether the form ends with xxx...

(? = Exp) match the position before exp

(?=hopeful)hope-> (? = Hopeful) + hope

(? = Hopeful) if the h index in hopeful is backward matched, hope is found.

hope(?=ful)-> Hope + (? = Ful)

Find hope first and then match the ful index.hope(?=ful)fulMatchinghopeful

You can assume that the match is to move the cursor to the text editor.MatchStart position of the text, and selectCaptureText.
Hope matches| Hope... The vertical line indicates the cursor position, and the next match starts after e.
(? Yes,The capture length is 0., The effect is equivalent to... | ful
The combination of the two is to match the entireHopeYes, but only hope is captured.

(? Hopeful) the matching effect is | hopeful, which matches the entire hopeful, and the next match still starts from h.
In the future, hope matches| Hope...
The effect is the same as the regular expression above.