• Donald H. (Donnie) Pinkston, III's avatar
    Documents and code changes for Assignment 3 · c7b4e8f9
    Donald H. (Donnie) Pinkston, III authored
    The design document and information document are included under the doc
    directory now.
    
    Added a lot of documentation, particularly to the Schema class.
    
    Made a few changes to the ArithmeticOperator and BooleanOperator
    classes' simplify() methods so that we can do some basic
    simplifications.
    
    Added the StatisticsUpdater so that it's easier for students to modify
    statistics based on selection predicates.
    
    Fixed a bug in SelectClause where ORDER BY clauses were using the
    FROM-clause schema rather than the SELECT-clause schema.
    c7b4e8f9
ArithmeticOperator.java 24.7 KB
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package edu.caltech.nanodb.expressions;


import java.math.BigDecimal;
import java.math.BigInteger;
import java.math.RoundingMode;
import java.time.Duration;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.Period;
import java.time.temporal.TemporalAmount;

import edu.caltech.nanodb.relations.ColumnInfo;
import edu.caltech.nanodb.relations.ColumnType;
import edu.caltech.nanodb.relations.SQLDataType;
import edu.caltech.nanodb.relations.Schema;
import edu.caltech.nanodb.relations.SchemaNameException;
import edu.caltech.nanodb.util.Pair;


/**
 * This class implements simple binary arithmetic operations.  The supported
 * operations are:
 * <ul>
 *   <li>addition, <tt>+</tt></li>
 *   <li>subtraction, <tt>-</tt></li>
 *   <li>multiplication, <tt>*</tt></li>
 *   <li>division, <tt>/</tt></li>
 *   <li>remainder, <tt>%</tt></li>
 *   <li>exponentiation, <tt>^</tt></li>
 * </ul>
 */
public class ArithmeticOperator extends Expression {

    /**
     * This enum specifies the arithmetic operations that this class can provide.
     * Each arithmetic operation also holds its string representation, which is
     * used when converting an arithmetic expression into a string for display.
     */
    public enum Type {
        ADD("+"),
        SUBTRACT("-"),
        MULTIPLY("*"),
        DIVIDE("/"),
        REMAINDER("%"),
        POWER("^");


        /** The string representation for each operator.  Used for printing. */
        private final String stringRep;

        /**
         * Construct a Type enum with the specified string representation.
         *
         * @param rep the string representation of the arithmetic operation
         */
        Type(String rep) {
            stringRep = rep;
        }

        /**
         * Accessor for the operator type's string representation.
         *
         * @return the string representation of the arithmetic operation
         */
        public String stringRep() {
            return stringRep;
        }


        /**
         * Given a string representation of an arithmetic operator, this
         * method returns the corresponding {@code Type} value.
         *
         * @param stringRep the string representation of the arithmetic
         *        operator
         *
         * @return the operator's corresponding type, or {@code null} if the
         *         type cannot be found
         */
        public static Type find(String stringRep) {
            for (Type t : values()) {
                if (t.stringRep.equals(stringRep))
                    return t;
            }

            // Couldn't find the corresponding operator type.
            return null;
        }
    }


    /** The kind of comparison, such as "subtract" or "multiply." */
    private Type type;

    /** The left expression in the comparison. */
    private Expression leftExpr;

    /** The right expression in the comparison. */
    private Expression rightExpr;



    public ArithmeticOperator(Type type, Expression lhs, Expression rhs) {
        if (type == null || lhs == null || rhs == null)
            throw new NullPointerException();

        leftExpr = lhs;
        rightExpr = rhs;

        this.type = type;
    }


    @Override
    public ColumnInfo getColumnInfo(Schema schema) throws SchemaNameException {
        ColumnInfo ltColInfo = leftExpr.getColumnInfo(schema);
        ColumnInfo rtColInfo = rightExpr.getColumnInfo(schema);

        SQLDataType resultSQLType = getSQLResultType(
            ltColInfo.getType().getBaseType(), rtColInfo.getType().getBaseType());

        ColumnType colType = new ColumnType(resultSQLType);
        return new ColumnInfo(toString(), colType);
    }


    private SQLDataType getSQLResultType(SQLDataType lType, SQLDataType rType) {
        // This array specifies the type-conversion sequence.  If at least one of
        // the arguments is type typeOrder[i], then both arguments are coerced to
        // that type.  (This is not entirely accurate at the moment, but is
        // sufficient for our needs.)
        SQLDataType[] typeOrder = {
            SQLDataType.NUMERIC, SQLDataType.DOUBLE, SQLDataType.FLOAT,
            SQLDataType.BIGINT, SQLDataType.INTEGER, SQLDataType.SMALLINT,
            SQLDataType.TINYINT
        };

        for (SQLDataType aTypeOrder : typeOrder) {
            if (lType == aTypeOrder || rType == aTypeOrder)
                return aTypeOrder;
        }

        // Just guess INTEGER.  Works for C...
        return SQLDataType.INTEGER;
    }


    public Object evaluate(Environment env) throws ExpressionException {
        // Evaluate the left and right subexpressions.
        Object lhsValue = leftExpr.evaluate(env);
        Object rhsValue = rightExpr.evaluate(env);

        // If either the LHS value or RHS value is NULL (represented by Java
        // null value) then the entire expression evaluates to NULL.
        if (lhsValue == null || rhsValue == null)
            return null;

        return evalObjects(type, lhsValue, rhsValue);
    }


    /**
     * This static helper method can be used to compute basic arithmetic
     * operations between two arguments.  It is of course used to evaluate
     * <tt>ArithmeticOperator</tt> objects, but it can also be used to evaluate
     * specific arithmetic operations within other components of the database
     * system.
     *
     * @param type the arithmetic operation to perform
     * @param aObj the first operand value for the operation
     * @param bObj the second operand value for the operation
     *
     * @return the result of the arithmetic operation
     *
     * @throws ExpressionException if the operand type is unrecognized
     */
    public static Object evalObjects(Type type, Object aObj, Object bObj) {
        // Coerce the values to both have the same numeric type.

        Pair coerced = TypeConverter.coerceArithmetic(aObj, bObj);

        Object result;

        if (coerced.value1 instanceof BigInteger) {
            result = evalBigIntegers(type, (BigInteger) coerced.value1,
                                           (BigInteger) coerced.value2);
        }
        else if (coerced.value1 instanceof BigDecimal) {
            result = evalBigDecimals(type, (BigDecimal) coerced.value1,
                                           (BigDecimal) coerced.value2);
        }
        else if (coerced.value1 instanceof Double) {
            result = evalDoubles(type, (Double) coerced.value1,
                                       (Double) coerced.value2);
        }
        else if (coerced.value1 instanceof Float) {
            result = evalFloats(type, (Float) coerced.value1,
                                      (Float) coerced.value2);
        }
        else if (coerced.value1 instanceof Long) {
            result = evalLongs(type, (Long) coerced.value1,
                                     (Long) coerced.value2);
        }
        else if (coerced.value1 instanceof Integer) {
            result = evalIntegers(type, (Integer) coerced.value1,
                                        (Integer) coerced.value2);
        }
        else if (coerced.value1 instanceof LocalDate &&
                 coerced.value2 instanceof LocalDate) {
            result = evalDates(type, (LocalDate) coerced.value1,
                                     (LocalDate) coerced.value2);
        }
        else if (coerced.value1 instanceof LocalTime &&
                 coerced.value2 instanceof LocalTime) {
            result = evalTimes(type, (LocalTime) coerced.value1,
                                     (LocalTime) coerced.value2);
        }
        else if (coerced.value1 instanceof LocalDateTime &&
                 coerced.value2 instanceof LocalDateTime) {
            result = evalDateTimes(type, (LocalDateTime) coerced.value1,
                                         (LocalDateTime) coerced.value2);
        }
        else if (coerced.value1 instanceof LocalDate &&
            coerced.value2 instanceof TemporalAmount) {
            result = evalDateInterval(type, (LocalDate) coerced.value1,
                (TemporalAmount) coerced.value2);
        }
        else if (coerced.value1 instanceof LocalTime &&
            coerced.value2 instanceof TemporalAmount) {
            result = evalTimeInterval(type, (LocalTime) coerced.value1,
                (TemporalAmount) coerced.value2);
        }
        else if (coerced.value1 instanceof LocalDateTime &&
            coerced.value2 instanceof TemporalAmount) {
            result = evalDateTimeInterval(type, (LocalDateTime) coerced.value1,
                (TemporalAmount) coerced.value2);
        }
        else if (coerced.value1 instanceof TemporalAmount &&
            coerced.value2 instanceof LocalDate) {
            result = evalIntervalDate(type, (TemporalAmount) coerced.value1,
                (LocalDate) coerced.value2);
        }
        else if (coerced.value1 instanceof TemporalAmount &&
            coerced.value2 instanceof LocalTime) {
            result = evalIntervalTime(type, (TemporalAmount) coerced.value1,
                (LocalTime) coerced.value2);
        }
        else if (coerced.value1 instanceof TemporalAmount &&
            coerced.value2 instanceof LocalDateTime) {
            result = evalIntervalDateTime(type, (TemporalAmount) coerced.value1,
                (LocalDateTime) coerced.value2);
        }
        else {
            throw new IllegalArgumentException("Cannot perform arithmetic on " +
                coerced.value1.getClass() + " and " + coerced.value2.getClass());
        }

        return result;
    }


    private static BigDecimal evalBigDecimals(Type type, BigDecimal a, BigDecimal b) {
        BigDecimal result;

        switch (type) {
        case ADD:
            result = a.add(b);
            break;

        case SUBTRACT:
            result = a.subtract(b);
            break;

        case MULTIPLY:
            result = a.multiply(b);
            break;

        case DIVIDE:
            if (b.equals(BigDecimal.ZERO))
                throw new DivideByZeroException();

            int scale = 10;  // TODO:  Scale?
            result = a.divide(b, scale, RoundingMode.HALF_UP);
            break;

        case REMAINDER:
            if (b.equals(BigDecimal.ZERO))
                throw new DivideByZeroException();

            result = a.remainder(b);
            break;

        case POWER:
            throw new ExpressionException("POWER is unsupported for BigDecimal");

        default:
            throw new ExpressionException("Unrecognized arithmetic type " + type);
        }

        return result;
    }


    private static BigInteger evalBigIntegers(Type type, BigInteger a, BigInteger b) {
        BigInteger result;

        switch (type) {
        case ADD:
            result = a.add(b);
            break;

        case SUBTRACT:
            result = a.subtract(b);
            break;

        case MULTIPLY:
            result = a.multiply(b);
            break;

        case DIVIDE:
            if (b.equals(BigInteger.ZERO))
                throw new DivideByZeroException();

            result = a.divide(b);
            break;

        case REMAINDER:
            if (b.equals(BigInteger.ZERO))
                throw new DivideByZeroException();

            result = a.remainder(b);
            break;

        case POWER:
            throw new ExpressionException("POWER is unsupported for BigInteger");

        default:
            throw new ExpressionException("Unrecognized arithmetic type " + type);
        }

        return result;
    }


    /**
     * This helper implements the arithmetic operations for <tt>Double</tt>
     * values.  Note that division of two <tt>Double</tt>s will produce a
     * <tt>Double</tt>.
     *
     * @param type the arithmetic operation to perform
     * @param a the first operand value for the operation
     * @param b the second operand value for the operation
     *
     * @return the result of the arithmetic operation
     *
     * @throws ExpressionException if the operand type is unrecognized
     */
    private static Double evalDoubles(Type type, Double a, Double b) {
        double result;

        switch (type) {
        case ADD:
            result = a + b;
            break;

        case SUBTRACT:
            result = a - b;
            break;

        case MULTIPLY:
            result = a * b;
            break;

        case DIVIDE:
            if (b == 0)
                throw new DivideByZeroException();

            result = a / b;
            break;

        case REMAINDER:
            if (b == 0)
                throw new DivideByZeroException();

            result = a % b;
            break;

        case POWER:
            if (a == 0 && b == 0)
                throw new ExpressionException("0**0 is undefined");

            result = Math.pow(a, b);
            break;

        default:
            throw new ExpressionException("Unrecognized arithmetic type " + type);
        }

        return result;
    }


    /**
     * This helper implements the arithmetic operations for <tt>Float</tt>
     * values.  Note that division of two <tt>Float</tt>s will produce a
     * <tt>Float</tt>.
     *
     * @param type the arithmetic operation to perform
     * @param a the first operand value for the operation
     * @param b the second operand value for the operation
     *
     * @return the result of the arithmetic operation
     *
     * @throws ExpressionException if the operand type is unrecognized
     */
    private static Float evalFloats(Type type, Float a, Float b) {
        float result;

        switch (type) {
        case ADD:
            result = a + b;
            break;

        case SUBTRACT:
            result = a - b;
            break;

        case MULTIPLY:
            result = a * b;
            break;

        case DIVIDE:
            if (b == 0)
                throw new DivideByZeroException();

            result = a / b;
            break;

        case REMAINDER:
            if (b == 0)
                throw new DivideByZeroException();

            result = a % b;
            break;

        case POWER:
            if (a == 0 && b == 0)
                throw new ExpressionException("0**0 is undefined");

            result = (float) Math.pow(a, b);
            break;

        default:
            throw new ExpressionException("Unrecognized arithmetic type " + type);
        }

        return result;  // Rely on boxing
    }


    /**
     * This helper implements the arithmetic operations for <tt>Long</tt>
     * values.  Note that division of two <tt>Long</tt>s will produce a
     * <tt>Double</tt>, not a <tt>Long</tt>.
     *
     * @param type the arithmetic operation to perform
     * @param a the first operand value for the operation
     * @param b the second operand value for the operation
     *
     * @return the result of the arithmetic operation
     *
     * @throws ExpressionException if the operand type is unrecognized
     */
    private static Object evalLongs(Type type, Long a, Long b) {
        long result;

        switch (type) {
        case ADD:
            result = a + b;
            break;

        case SUBTRACT:
            result = a - b;
            break;

        case MULTIPLY:
            result = a * b;
            break;

        case DIVIDE:
            if (b == 0)
                throw new DivideByZeroException();

            result = a / b;
            break;

        case REMAINDER:
            if (b == 0)
                throw new DivideByZeroException();

            result = a % b;
            break;

        case POWER:
            if (a == 0 && b == 0)
                throw new ExpressionException("0**0 is undefined");

            result = (long) Math.pow(a, b);
            break;

        default:
            throw new ExpressionException("Unrecognized arithmetic type " + type);
        }

        return result;  // Rely on boxing
    }


    /**
     * This helper implements the arithmetic operations for <tt>Integer</tt>
     * values.  Note that division of two <tt>Integer</tt>s will produce a
     * <tt>Double</tt>, not an <tt>Integer</tt>.
     *
     * @param type the arithmetic operation to perform
     * @param a the first operand value for the operation
     * @param b the second operand value for the operation
     *
     * @return the result of the arithmetic operation
     *
     * @throws ExpressionException if the operand type is unrecognized
     */
    private static Object evalIntegers(Type type, Integer a, Integer b) {
        int result;

        switch (type) {
        case ADD:
            result = a + b;
            break;

        case SUBTRACT:
            result = a - b;
            break;

        case MULTIPLY:
            result = a * b;
            break;

        case DIVIDE:
            if (b == 0)
                throw new DivideByZeroException();

            result = a / b;
            break;

        case REMAINDER:
            if (b == 0)
                throw new DivideByZeroException();

            result = a % b;
            break;

        case POWER:
            if (a == 0 && b == 0)
                throw new ExpressionException("0**0 is undefined");

            result = (int) Math.pow(a, b);
            break;

        default:
            throw new ExpressionException("Unrecognized arithmetic type " + type);
        }

        return result;  // Rely on boxing
    }


    private static Object evalDateTimes(Type type, LocalDateTime a, LocalDateTime b) {
        if (a == null || b == null)
            return null;

        if (type == Type.SUBTRACT) {
            return Duration.between(b, a);
        }
        else {
            throw new IllegalArgumentException(
                "Cannot perform requested operation " + type +
                " on LocalDateTime objects");
        }
    }


    private static Object evalDates(Type type, LocalDate a, LocalDate b) {
        if (a == null || b == null)
            return null;

        if (type == Type.SUBTRACT) {
            return Period.between(b, a);
        }
        else {
            throw new IllegalArgumentException(
                "Cannot perform requested operation " + type +
                    " on LocalDate objects");
        }
    }


    private static Object evalTimes(Type type, LocalTime a, LocalTime b) {
        if (a == null || b == null)
            return null;

        if (type == Type.SUBTRACT) {
            return Duration.between(b, a);
        }
        else {
            throw new IllegalArgumentException(
                "Cannot perform requested operation " + type +
                    " on LocalTime objects");
        }
    }


    private static Object evalDateInterval(Type type, LocalDate a, TemporalAmount b) {
        if (a == null || b == null)
            return null;

        if (type == Type.ADD) {
            return a.plus(b);
        }
        else if (type == Type.SUBTRACT) {
            return a.minus(b);
        }
        else {
            throw new IllegalArgumentException(
                "Cannot perform requested operation " + type +
                    " on LocalDate and TemporalAmount objects");
        }
    }


    private static Object evalTimeInterval(Type type, LocalTime a,
                                           TemporalAmount b) {
        if (a == null || b == null)
            return null;

        if (type == Type.ADD) {
            return a.plus(b);
        }
        else if (type == Type.SUBTRACT) {
            return a.minus(b);
        }
        else {
            throw new IllegalArgumentException(
                "Cannot perform requested operation " + type +
                    " on LocalTime and TemporalAmount objects");
        }
    }


    private static Object evalDateTimeInterval(Type type, LocalDateTime a,
                                               TemporalAmount b) {
        if (a == null || b == null)
            return null;

        if (type == Type.ADD) {
            return a.plus(b);
        }
        else if (type == Type.SUBTRACT) {
            return a.minus(b);
        }
        else {
            throw new IllegalArgumentException(
                "Cannot perform requested operation " + type +
                    " on LocalDateTime and TemporalAmount objects");
        }
    }


    private static Object evalIntervalDate(Type type, TemporalAmount a,
                                           LocalDate b) {
        if (a == null || b == null)
            return null;

        if (type == Type.ADD) {
            return b.plus(a);
        }
        else {
            throw new IllegalArgumentException(
                "Cannot perform requested operation " + type +
                    " on TemporalAmount and LocalDate objects");
        }
    }


    private static Object evalIntervalTime(Type type, TemporalAmount a,
                                           LocalTime b) {
        if (a == null || b == null)
            return null;

        if (type == Type.ADD) {
            return b.plus(a);
        }
        else {
            throw new IllegalArgumentException(
                "Cannot perform requested operation " + type +
                    " on TemporalAmount and LocalTime objects");
        }
    }


    private static Object evalIntervalDateTime(Type type, TemporalAmount a,
                                               LocalDateTime b) {
        if (a == null || b == null)
            return null;

        if (type == Type.ADD) {
            return b.plus(a);
        }
        else {
            throw new IllegalArgumentException(
                "Cannot perform requested operation " + type +
                    " on TemporalAmount and LocalDateTime objects");
        }
    }


    @Override
    public Expression traverse(ExpressionProcessor p) {
        p.enter(this);
        leftExpr = leftExpr.traverse(p);
        rightExpr = rightExpr.traverse(p);
        return p.leave(this);
    }


    /**
     * Returns a string representation of this arithmetic expression and its
     * subexpressions, including parentheses where necessary to specify
     * precedence.
     */
    @Override
    public String toString() {
        // Convert all of the components into string representations.
        String leftStr = leftExpr.toString();
        String rightStr = rightExpr.toString();
        String opStr = " " + type.stringRep() + " ";

        // Figure out if I need parentheses around the subexpressions.

        if (type == Type.MULTIPLY || type == Type.DIVIDE || type == Type.REMAINDER) {
            if (leftExpr instanceof ArithmeticOperator) {
                ArithmeticOperator leftOp = (ArithmeticOperator) leftExpr;
                if (leftOp.type == Type.ADD || leftOp.type == Type.SUBTRACT)
                    leftStr = "(" + leftStr + ")";
            }

            if (rightExpr instanceof ArithmeticOperator) {
                ArithmeticOperator rightOp = (ArithmeticOperator) rightExpr;
                if (rightOp.type == Type.ADD || rightOp.type == Type.SUBTRACT)
                    rightStr = "(" + rightStr + ")";
            }
        }

        return leftStr + opStr + rightStr;
    }


    /**
     * Simplifies an arithmetic expression, computing as much of the expression
     * as possible.
     */
    @Override
    public Expression simplify() {
        leftExpr = leftExpr.simplify();
        rightExpr = rightExpr.simplify();

        if (!leftExpr.hasSymbols())
            leftExpr = new LiteralValue(leftExpr.evaluate());

        if (!rightExpr.hasSymbols())
            rightExpr = new LiteralValue(rightExpr.evaluate());

        if (!hasSymbols())
            return new LiteralValue(evaluate());

        return this;
    }


    /**
     * Checks if the argument is an expression with the same structure, but not
     * necesarily the same references.
     *
     * @param obj the object to which we are comparing
     */
    @Override
    public boolean equals(Object obj) {
        if (obj instanceof ArithmeticOperator) {
            ArithmeticOperator other = (ArithmeticOperator) obj;
            return (type.equals(other.type) &&
                    leftExpr.equals(other.leftExpr) &&
                    rightExpr.equals(other.rightExpr));
        }
        return false;
    }


    /**
     * Computes the hashcode of an Expression.  This method is used to see if
     * two expressions CAN be equal.
     */
    @Override
    public int hashCode() {
        int hash = 7;

        hash = 31 * hash + type.hashCode();

        hash = 31 * hash + leftExpr.hashCode();
        hash = 31 * hash + rightExpr.hashCode();

        return hash;
    }


    /** Creates a copy of expression. */
    @Override
    protected Object clone() throws CloneNotSupportedException {
        ArithmeticOperator expr = (ArithmeticOperator)super.clone();

        // Type is immutable, copy it.
        expr.type = this.type;

        // Clone the subexpressions
        expr.leftExpr = (Expression) leftExpr.clone();
        expr.rightExpr = (Expression) rightExpr.clone();

        return expr;
    }
}