public class CharStack  {
  
  private static final int defaultSize = 1000;
    
  private char [] data;
  private int numElements = 0;
  
  CharStack () {
    data = new char[defaultSize];
  }
  
  CharStack (int initialSize) {
    data = new char[initialSize];
  }
  
  public boolean isEmpty() {
    return (numElements == 0);
  }
  
  public void push(char c) {
    if (numElements == data.length) {
      char [] tmpData = new char [Math.max(2*data.length, 1)];
      for (int i = 0; i<numElements; i++)
        tmpData[i]=data[i];
      data = tmpData;
    }
    data[numElements++]=c;
  }
    
  public char pop () {
    return data[--numElements];
  }
}