Difference between matches and find in Java Regex

Question

I am trying to understand the difference between matches   and find     According to the Javadoc   from what I understand   matches   will search the entire string even if it finds what it is looking for  and find   will stop when it finds what it is looking for   If that assumption is correct  I cannot see whenever you would want to use matches   instead of find    unless you want to count the number of matches it finds   In my opinion the String class should then have find   instead of matches   as an inbuilt method   So to summarize    Is my assumption correct  When is it useful to use matches   instead of find

User · Accepted Answer

matches tries to match the expression against the entire string and implicitly add a   at the start and   at the end of your pattern  meaning it will not look for a substring  Hence the output of this code   public static void main String   args  throws ParseException       Pattern p   Pattern compile    d  d  d        Matcher m   p matcher  a123b        System out println m find         System out println m matches          p   Pattern compile     d  d  d         m   p matcher  123        System out println m find         System out println m matches           output  true false true true      123 is a substring of a123b so the find   method outputs true  matches   only  sees  a123b which is not the same as 123 and thus outputs false

User · Answer

find   will consider the sub-string against the regular expression where as matches   will consider complete expression    find   will returns true only if the sub-string of the expression matches the pattern   public static void main String   args            Pattern p   Pattern compile    d            String candidate    Java123           Matcher m   p matcher candidate            if  m    null               System out println m find      true             System out println m matches      false

User · Answer

matches   will only return true if the full string is matched  find   will try to find the next occurrence within the substring that matches the regex  Note the emphasis on  the next   That means  the result of calling find   multiple times might not be the same  In addition  by using find   you can call start   to return the position the substring was matched    final Matcher subMatcher   Pattern compile    d    matcher  skrf35kesruytfkwu4ty7sdfs    System out println  Found      subMatcher matches     System out println  Found      subMatcher find       - position     subMatcher start     System out println  Found      subMatcher find       - position     subMatcher start     System out println  Found      subMatcher find       - position     subMatcher start     System out println  Found      subMatcher find     System out println  Found      subMatcher find     System out println  Matched      subMatcher matches      System out println  -----------    final Matcher fullMatcher   Pattern compile     w     matcher  skrf35kesruytfkwu4ty7sdfs    System out println  Found      fullMatcher find       - position     fullMatcher start     System out println  Found      fullMatcher find     System out println  Found      fullMatcher find     System out println  Matched      fullMatcher matches     System out println  Matched      fullMatcher matches     System out println  Matched      fullMatcher matches     System out println  Matched      fullMatcher matches       Will output    Found  false Found  true - position 4 Found  true - position 17 Found  true - position 20 Found  false Found  false Matched  false ----------- Found  true - position 0 Found  false Found  false Matched  true Matched  true Matched  true Matched  true   So  be careful when calling find   multiple times if the Matcher object was not reset  even when the regex is surrounded with   and   to match the full string

User · Answer

matches return true if the whole string matches the given pattern  find tries to find a substring that matches the pattern

User · Answer

matches    does not buffer  but find   buffers  find   searches to the end of the string first  indexes the result  and return the boolean value and corresponding index    That is why when you have a code like   1 Pattern compile   a-z      2 Pattern matcher  0a1b1c3d4     3 int count   0   4 while matcher find      5 count        At 4  The regex engine using the pattern structure will read through the whole of your code  index to index as specified by the regex single character  to find at least one match  If such match is found  it will be indexed then the loop will execute based on the indexed result else if it didn t do ahead calculation like which matches    does not  The while statement would never execute since the first character of the matched string is not an alphabet

[java] Difference between matches() and find() in Java Regex

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