SE450: Composite: With a static factory [14/24] Previous pageContentsNext page

file:composite/two/Main.java [source] [doc-public] [doc-private]
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package composite.two;
public class Main {
  public static void main(String[] args) {
    Expr one = ExprFactory.newConst(1);
    Expr onePtwo = ExprFactory.newPlus
        (ExprFactory.newConst(1), ExprFactory.newConst(2));
    Expr threeMfour = ExprFactory.newMult
        (ExprFactory.newConst(3), ExprFactory.newConst(4));
    Expr m = ExprFactory.newMinus (onePtwo, threeMfour);
    Expr n = ExprFactory.newQuot (m, ExprFactory.newConst(5));

    System.out.println(n);
    System.out.println("Value: " + n.eval());
  }
}

file:composite/two/Expr.java [source] [doc-public] [doc-private]
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package composite.two;
public interface Expr {
  int eval();
}

file:composite/two/ExprFactory.java [source] [doc-public] [doc-private]
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package composite.two;
public class ExprFactory {
  private ExprFactory() {}
  static public Expr newConst(int v) {
    return new Const(v);
  }
  static public Expr newPlus(Expr l, Expr r) {
    return new Plus(l, r);
  }
  static public Expr newMinus(Expr l, Expr r) {
    return new Minus(l, r);
  }
  static public Expr newMult(Expr l, Expr r) {
    return new Mult(l, r);
  }
  static public Expr newQuot(Expr l, Expr r) {
    return new Quot(l, r);
  }

  private static class Const implements Expr {
    private final int v;
    public Const(int v) {
      this.v = v;
    }
    public int eval() {
      return v;
    }
    public String toString() {
      return Integer.toString(v);
    }
  }

  private static class Plus implements Expr {
    private final Expr l;
    private final Expr r;
    public Plus(Expr l, Expr r) {
      if ((l == null) || (r == null)) {
        throw new IllegalArgumentException();
      }
      this.l = l;
      this.r = r;
    }
    public int eval() {
      return l.eval() + r.eval();
    }
    public String toString() {
      return l.toString() + " " + r.toString() + " +";
    }
  }

  private static class Minus implements Expr {
    private final Expr l;
    private final Expr r;
    public Minus(Expr l, Expr r) {
      if ((l == null) || (r == null)) {
        throw new IllegalArgumentException();
      }
      this.l = l;
      this.r = r;
    }
    public int eval() {
      return l.eval() - r.eval();
    }
    public String toString() {
      return l.toString() + " " + r.toString() + " -";
    }
  }

  private static class Mult implements Expr {
    private final Expr l;
    private final Expr r;
    public Mult(Expr l, Expr r) {
      if ((l == null) || (r == null)) {
        throw new IllegalArgumentException();
      }
      this.l = l;
      this.r = r;
    }
    public int eval() {
      return l.eval() * r.eval();
    }
    public String toString() {
      return l.toString() + " " + r.toString() + " *";
    }
  }

  private static class Quot implements Expr {
    private final Expr l;
    private final Expr r;
    public Quot(Expr l, Expr r) {
      if ((l == null) || (r == null)) {
        throw new IllegalArgumentException();
      }
      this.l = l;
      this.r = r;
    }
    public int eval() {
      return l.eval() / r.eval();
    }
    public String toString() {
      return l.toString() + " " + r.toString() + " /";
    }
  }
}

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