// Textbook fragment 07.30
/** Class for a variable of an arithmetic expression. */
public class ExpressionVariable extends ExpressionTerm {
  protected Integer var;
  public ExpressionVariable(Integer x) { var = x; }
  public void setVariable(Integer x) { var = x; }
  public Integer getValue() { return var; }
  public String toString() { return var.toString(); }
}