boolean flag = str.matches("正規表現");

String result = str.replaceFirst("正規表現","置換文字列");
String result = str.replaceAll("正規表現","置換文字列");

String[] strs = str.split("正規表現");

boolean flag = Pattern.matches("正規表現","文字列");

Pattern p = Pattern.compile("正規表現");
Matcher m = p.matcher("置換対象文字列");
String result = m.replaceFirst("置換文字列");
String result = m.replaceAll("置換文字列");

Pattern p = Pattern.compile("正規表現");
String[] strs = p.split("置換対象文字列");

import java.util.regex.*;