// StringBufferDemo.java

import java.util.*;

public class StringBufferDemo {
  public static void testMyStringBuffer() {
    // first, demontrate StringBuffer
    StringBuffer s = new StringBuffer("foo");
    s.append("blat");
    assert(s.toString().equals("fooblat"));
    // now make our code do the same thing
    MyStringBuffer ms = new MyStringBuffer("foo");
    assert(ms.toString().equals("foo"));
    ms.append("blat");
    assert(ms.toString().equals("fooblat"));
  }

  public static void main(String[] args) {
    testMyStringBuffer();
  }
}

class MyStringBuffer {
  private char[] charArray;

  public MyStringBuffer(String s) {
    // for now:  just store the entire string in the charArray
    charArray = new char[s.length()];
    for (int i=0; i<s.length(); i++) charArray[i] = s.charAt(i);
  }

  public void append(String s) {
    // for now, create a new array which appends existing array and parameter "s"
    char[] newArray = new char[charArray.length + s.length()];
    for (int i=0; i<charArray.length; i++) newArray[i] = charArray[i];
    for (int i=0; i<s.length(); i++) newArray[charArray.length+i] = s.charAt(i);
    charArray = newArray;
  }

  public String toString() {
    return new String(this.charArray);
  }
}