ExpressionTree.java

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package aud.example.expr;
 
import aud.BinaryTree;
 
import aud.util.GraphvizDecorator;
import aud.util.SimpleDecorator;
 
public class ExpressionTree extends BinaryTree<AtomicExpression> {
  public ExpressionTree(AtomicExpression atom,
                        ExpressionTree left,ExpressionTree right) {
    super(atom,left,right);
    if (atom.node_!=null)
      throw new RuntimeException("ExpressionTree: AtomicExpression "+
                                 "is already bound to another node!");
    atom.node_=this;
  }
  public ExpressionTree(AtomicExpression atom) {
    this(atom,null,null);
  }
 
  public double getValue() { return getData().getValue(); }
 
  @Override public void setData(AtomicExpression data) {
    if (data.node_!=null)
      throw new RuntimeException("ExpressionTree#setData: AtomicExpression "+
                                 "is already bound to an ExpressionTree node!");
    super.setData(data);
    data.node_=this; // Note: Side effect on data!
  }
 
  @Override public String toString() {
    if (getData().isTerminal())
      return getData().toString();
 
    assert(!isLeaf());
    assert(getData().isOperator());
 
    String term=(!isRoot() ? "(" : "");
    if (getRight()!=null)
      term+=getLeft().toString()+getData().toString()+getRight().toString();
    else
      term+=getData().toString()+getLeft().toString(); // unary operator
 
    if (!isRoot()) term+=")";
 
    return term;
  }
 
  static final GraphvizDecorator decorator = new SimpleDecorator();
  @Override public GraphvizDecorator getDecorator() {
    return decorator;
  }
 
 
  public static void main(String[] args) {
    ExpressionTree t=new ExpressionTree
      (new Minus(),
       new ExpressionTree
       (new Times(),
        new ExpressionTree(new Plus(),
                           new ExpressionTree(new Number(2)),
                           new ExpressionTree(new Number(3))),
        new ExpressionTree(new Number(4))
       ),
       new ExpressionTree(new Number(5))
      );
 
    System.out.println(t);
    System.out.println(t.getValue());
    System.out.println(t.postorder().toString());
 
    t=new ExpressionTree(new Plus(),
                         t,new ExpressionTree(new Symbol("x")));
    System.out.println(t);
    System.out.println(t.getValue()); // throws
  }
}