Error: cannot find symbol

[leo_search1]

No sè el por què me da error al compilar el siguiente codigo.

public class HelloWorld{

public static void main(String []args){
Pattern pattern = Pattern.compile("here");
Matcher matcher = pattern.matcher("input here");

while (matcher.find()) {
System.out.println(matcher.group());
}
}
}


ERROR

^
symbol: class Pattern
location: class HelloWorld
HelloWorld.java:4: error: cannot find symbol
Pattern pattern = Pattern.compile("here");
^
symbol: variable Pattern
location: class HelloWorld
HelloWorld.java:5: error: cannot find symbol
Matcher matcher = pattern.matcher("input here");
^
symbol: class Matcher
location: class HelloWorld
3 errors
sh-4.3$ ^C

A que se debe el error?

Gracias.