/** 
 * String List Collection Class
 * Demonstration using arrays to implement a list
 * CSE 142 lecture, 2/03.  HP
 */
public class StringList {
  // instance variables
  private String[] strings;         // Strings in this StringList are stored in
  private int      numStrings;      //   strings[0..numStrings-1]
  
  
  /** Construct a new empty StringList with the given capacity */
  public StringList(int capacity) {
    strings = new String[capacity];
    numStrings = 0;
  }
  
  
  /**
   *  Add str to this StringList if room available and return true; 
   *  otherwise return false
   */
  public boolean add(String str) {
    if (numStrings < strings.length) {
      strings[numStrings] = str;
      numStrings++;
      return true;
    } else {
      return false;
    }
  }
  
  
  /** Return the current size of this StringList */
  public int size() {
    return numStrings;
  }
  
  
  /** Remove all strings from this StringList */
  public void clear() {
    // null out string references so the space can be recycled if not otherwise in use
    for (int k = 0; k < numStrings; k++) {
      strings[k] = null;
    }
    // record that the list is now empty
    numStrings = 0;
  }
  
  
  /** Return the string at position pos, or null if pos is out of bounds */
  public String get(int pos) {
    if (pos < 0 || pos >= numStrings) {
      return null;
    } else {
      return strings[pos];
    }
  }
  
  
  /**
   *  Store str in this StringList at position pos if pos is in bounds
   *  and return the previous string at that position.  If pos is out of
   *  bounds, return null without altering this StringList.
   */
  public String set(int pos, String str) {
    if (pos < 0 || pos >= numStrings) {
      return null;
    } else {
      String oldString = strings[pos];
      strings[pos] = str;
      return oldString;
    }
  }
  
  
  /** Return whether this StringList contains str */
  public boolean contains(String str) {
    // linear search
    for (int k = 0; k < numStrings; k++) {
      if (str.equals(strings[k])) {
        return true;
      }
    }
    return false;
  }
  
  
  /** Return a string representation of this StringList */
  public String toString() {
    String result = "[";
    if (numStrings > 0) {
      result = result + strings[0];
      for (int k = 1; k < numStrings; k++) {
        result = result + ", " + strings[k];
      }
    }
    result = result + "]";
    return result;
  }
}