SE450: Composite: Example [12/24] Previous pageContentsNext page

I will discuss these notes.

file:composite/one/Main.java [source] [doc-public] [doc-private]
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package composite.one;
public class Main {
  public static void main(String[] args) {
    Expr one = new Const(1);
    Expr onePtwo = new Plus (new Const(1), new Const(2));
    Expr threeMfour = new Mult (new Const(3), new Const(4));
    Expr m = new Minus (onePtwo, threeMfour);
    Expr n = new Quot (m, new Const(5));

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

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

final 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);
  }
}

final 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() + " +";
  }
}

final 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() + " -";
  }
}

final 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() + " *";
  }
}

final 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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