Matcher matches = Pattern.compile("T\d+").matcher("T234bird");
System.out.println(matches.lookingAt()); //after running this, find() will return false
while (matches.find())
    System.out.println(matches.group());
//Output: true

Matcher matches = Pattern.compile("T\d+").matcher("T234bird");
//System.out.println(matches.lookingAt()); //without this, find() will return true
while (matches.find())
    System.out.println(matches.group());
//Output: T234

Matcher matches = Pattern.compile("T\d+").matcher("T234bird");
while (matches.lookingAt())
    System.out.println(matches.group());
//Output: T234 T234 T234 T234 ... till crash
//I understand why this happens. It's not my question but I just included it in case someone may try to suggest it

Matcher matches = Pattern.compile("T\d+").matcher("T234bird");
if(matches.lookingAt())
    System.out.println(matches.group());
//Output: T234

Matcher matches = Pattern.compile("T\d+").matcher("T234bird");
if (matches.lookingAt())
    System.out.println(matches.group());

Matcher matches = Pattern.compile("^T\d+").matcher("T234bird");
if (matches.find())
    System.out.println(matches.group());