pattern.matcher() vs pattern.matches()

Question

I am wondering why the results of the java regex pattern.matcher() and pattern.matches() differ when provided the same regular expression and same string

String str = "hello+"; Pattern pattern = Pattern.compile("\\+"); Matcher matcher = pattern.matcher(str);  while (matcher.find()) {     System.out.println("I found the text " + matcher.group() + " starting at "          + "index " + matcher.start() + " and ending at index " + matcher.end()); }  System.out.println(java.util.regex.Pattern.matches("\\+", str)); 

The result of the above are:

I found the text + starting at index 5 and ending at index 6 false 

I found that using an expression to match the full string works fine in case of matches(".*\\+").

Answer 1

pattern.matcher(String s) returns a Matcher that can find patterns in the String s. pattern.matches(String str) tests, if the entire String (str) matches the pattern.

In brief (just to remember the difference):

• pattern.matcher - test if the string contains-a pattern
• pattern.matches - test if the string is-a pattern

Answer 2

Matcher.find() attempts to find the next subsequence of the input sequence that matches the pattern.

Pattern.matches(String regex, CharSequence input) compiles the regex into a Matcher and returns Matcher.matches().

Matcher.matches attempts to match the entire region (string) against the pattern (Regex).

So, in your case, the Pattern.matches("\\+", str) returns a false since str.equals("+") is false.