Akka/Scala example source code file (Expression.java)

This example Akka source code file (Expression.java) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Akka and Scala source code examples by using tags.

All credit for the original source code belongs to akka.io; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Akka tags/keywords

abstractexpression, add, const, divide, expression, multiply, override, string

The Expression.java Akka example source code

package supervision;

// Represents an arithmetic expression involving integer numbers
public interface Expression {

  public Expression getLeft();

  public Expression getRight();

  // Basic arithmetic operations that are supported by the ArithmeticService. Every
  // operation except the constant value has a left and right side. For example
  // the addition in (3 * 2) + (6 * 6) has the left side (3 * 2) and the right
  // side (6 * 6).
  public static abstract class AbstractExpression implements Expression {
    private final Expression left;
    private final Expression right;
    private final String operator;

    protected AbstractExpression(Expression left, Expression right, String operator) {
      this.left = left;
      this.right = right;
      this.operator = operator;
    }

    public Expression getLeft() {
      return left;
    }

    public Expression getRight() {
      return right;
    }

    @Override
    public boolean equals(Object o) {
      if (this == o) return true;
      if (!(o instanceof AbstractExpression)) return false;

      AbstractExpression that = (AbstractExpression) o;

      if (!left.equals(that.left)) return false;
      if (!operator.equals(that.operator)) return false;
      if (!right.equals(that.right)) return false;

      return true;
    }

    @Override
    public int hashCode() {
      int result = left.hashCode();
      result = 31 * result + right.hashCode();
      result = 31 * result + operator.hashCode();
      return result;
    }

    @Override
    public String toString() {
      return "(" + getLeft() + " " + operator + " " + getRight() + ")";
    }
  }

  public static final class Add extends AbstractExpression {
    public Add(Expression left, Expression right) {
      super(left, right, "+");
    }
  }

  public static final class Multiply extends AbstractExpression {
    public Multiply(Expression left, Expression right) {
      super(left, right, "*");
    }
  }

  public static final class Divide extends AbstractExpression {
    public Divide(Expression left, Expression right) {
      super(left, right, "/");
    }
  }

  public static final class Const implements Expression{
    private final int value;

    public Const(int value) {
      this.value = value;
    }

    @Override
    public Expression getLeft() {
      return this;
    }

    @Override
    public Expression getRight() {
      return this;
    }

    public int getValue() {
      return value;
    }

    @Override
    public boolean equals(Object o) {
      if (this == o) return true;
      if (!(o instanceof Const)) return false;

      Const aConst = (Const) o;

      if (value != aConst.value) return false;

      return true;
    }

    @Override
    public int hashCode() {
      return value;
    }

    @Override
    public String toString() {
      return String.valueOf(value);
    }
  }
}