PostFix

 
public class PostFixTest {
 private ArrayList<String>stack = new ArrayList<String>(); 
 
 @Test
 public void test1() {
  StringBuffer sb = new StringBuffer();
  ArrayList<String>arr = new ArrayList<String>();
  String s = "(1+2*(10+20-(7*10)-1))";
  Pattern p = Pattern.compile("(\\d+)|([\\+\\-\\*\\/])|([\\(\\)])");
  Matcher m = p.matcher(s);
  int i;
  
  while(m.find()) {
   for(i = 1; i <= m.groupCount(); i++) {
    if(m.group(i) == null) continue;
    arr.add(m.group(i));
   }
  }
  
  for(i = 0; i < arr.size(); i++) {
   char w = arr.get(i).charAt(0);
   if(w == '+' || w == '-' || w == '*' || w == '/') {
    push(arr.get(i));
   }else if(w == '(') {
   }else if(w == ')') {
    sb.append(pop() + " ");
   }else {
    sb.append(arr.get(i) + " ");
   }
  }
  
  while((s = pop()) != null) {
   sb.append(s + " ");
  }
  
  System.out.println(sb.toString());
 }
 
 public void push(String str) {
  stack.add(str);
 }
 
 public String pop() {
  if(stack.size() <= 0) {
   return null;
  }
  int pos = stack.size()-1;
  String str = stack.get(pos);
  stack.remove(pos);
  return str;
 }
}