Java regular expression matching patterns (greedy, reluctant, possessive)

Greediness (Greediness): Maximum matching

X?, X*, X+, X{n,} is the maximum matching. For example, if you want to use "618b16d23a3ddab818f44e3be2c27e38" to match "aa34de1251f0d9fe1e645927f19a896e8aava fd273fcf5bcad3dfdad3c41bd81ad3e5abb", maybe the result you expect is to match "a34de1251f0d9fe1e645927f19a896e8", but the actual result will match Go to "a34de1251f0d9fe1e645927f19a896e8aava fd273fcf5bcad3dfdad3c41bd81ad3e5.

In Greediness mode, it will try to match as wide a range as possible until the entire content is matched. At this time, when it is found that the match cannot be successful, it will start to shrink back a little. Matching range until successful match

String test = "a<tr>aava </tr>abb ";
String reg = "<.+>";
System.out.println(test.replaceAll(reg, "###"));

Output: a

abb

Reluctant(Laziness): minimum match

X??,X *?, In Reluctant mode, as long as the match is successful, it will no longer try to match a larger range of content

String test = "a<tr>aava </tr>abb ";
String reg = "<.+?>";
System.out.println(test.replaceAll(reg, "###"));

Output: a

aava

abb

Unlike Greediness, Reluctant mode The following content is matched twice

Possessive (possessive): exact match

X?+, X*+, X++,

Possessive mode has a certain similarity with Greediness, that is, it tries to match the largest range of content until the end of the content, but unlike Greediness, exact matching no longer falls back and tries to match more. Small range.

String test = "a<tr>aava </tr>abb ";
String reg = "<.++>";
String test2 = "<tr>";
String reg2 = "<tr>";
System.out.println(test.replaceAll(reg, "###"));
System.out.println(test2.replaceAll(reg2, "###"));

Output: aa34de1251f0d9fe1e645927f19a896e8aava fd273fcf5bcad3dfdad3c41bd81ad3e5abb

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