// Compile regular expression
String patternStr = "b";
Pattern pattern = Pattern.compile(patternStr);

// Determine if there is an exact match
CharSequence inputStr = "a b c";
Matcher matcher = pattern.matcher(inputStr);
boolean matchFound = matcher.matches(); // false

// Try a different input
matcher.reset("b");
matchFound = matcher.matches();         // true

// Determine if pattern matches beginning of input
matchFound = matcher.lookingAt();       // false