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+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+import pl.edu.mimuw.cloudatlas.model.Value;
+
+/**
+ * A single value stored as an attribute.
+ */
+public abstract class Value {
+	/**
+	 * An operation that may be performed on values.
+	 */
+	public enum Operation {
+		EQUAL, COMPARE, ADD, SUBTRACT, MULTIPLY, DIVIDE, MODULO, AND, OR, REG_EXPR, NEGATE, VALUE_SIZE,
+	}
+	
+	/**
+	 * Gets type of this value.
+	 * 
+	 * @return type of this value
+	 */
+	public abstract Type getType();
+	
+	/**
+	 * Indicates whether this value is null. Distinct from a <code>Value</code> reference that is <code>null</code>
+	 * itself.
+	 * 
+	 * @return true if and only if this value is null
+	 */
+	public abstract boolean isNull();
+	
+	protected final void sameTypesOrThrow(Value value, Operation operation) {
+		if(!getType().isCompatible(value.getType()))
+			throw new IncompatibleTypesException(getType(), value.getType(), operation);
+	}
+	
+	/**
+	 * Checks whether this value is equal to the specified one (operator ==).
+	 * 
+	 * @param value the right side of the operator
+	 * @return a <code>ValueBoolean</code> representing true if and only if both values are equal
+	 * @throws UnsupportedValueOperationException if this operation is unsupported for these values
+	 */
+	public Value isEqual(Value value) {
+		throw new UnsupportedValueOperationException(getType(), Operation.EQUAL);
+	}
+	
+	/**
+	 * Indicates whether this object is equal to another one.
+	 * 
+	 * @param object the object to check
+	 * @return whether two objects are equal
+	 */
+	@Override
+	public boolean equals(Object object) {
+		if(!(object instanceof Value))
+			return false;
+		return ((ValueBoolean)isEqual((Value)object)).getValue();
+	}
+	
+	/**
+	 * Checks whether this value is lower than the specified one (operator <=).
+	 * 
+	 * @param value the right side of the operator
+	 * @return a <code>ValueBoolean</code> representing true if and only if this value is lower than the provided one
+	 * @throws UnsupportedValueOperationException if this operator is unsupported for these values (for example
+	 * incompatible or non-numeric types)
+	 */
+	public Value isLowerThan(Value value) {
+		throw new UnsupportedValueOperationException(getType(), Operation.COMPARE);
+	}
+	
+	/**
+	 * Returns a new value created by adding argument to this value (operator +).
+	 * 
+	 * @param the right side of the operator
+	 * @return a sum of two values
+	 * @throws UnsupportedValueOperationException if this operator is unsupported for these values (for example
+	 * incompatible or non-numeric types)
+	 */
+	public Value addValue(Value value) {
+		// name clash with add from List interface
+		throw new UnsupportedValueOperationException(getType(), Operation.ADD);
+	}
+	
+	/**
+	 * Returns a new value created by subtracting argument from this value (operator -).
+	 * 
+	 * @param the right side of the operator
+	 * @return a difference of two values
+	 * @throws UnsupportedValueOperationException if this operator is unsupported for these values (for example
+	 * incompatible or non-numeric types)
+	 */
+	public Value subtract(Value value) {
+		throw new UnsupportedValueOperationException(getType(), Operation.SUBTRACT);
+	}
+	
+	/**
+	 * Returns a new value created by multiplying this value by an argument (operator *).
+	 * 
+	 * @param the right side of the operator
+	 * @return a product of two values
+	 * @throws UnsupportedValueOperationException if this operator is unsupported for these values (for example
+	 * incompatible or non-numeric types)
+	 */
+	public Value multiply(Value value) {
+		throw new UnsupportedValueOperationException(getType(), Operation.MULTIPLY);
+	}
+	
+	/**
+	 * Returns a new value created by dividing this value by an argument (operator /).
+	 * 
+	 * @param the right side of the operator
+	 * @return a quotient of two values
+	 * @throws UnsupportedValueOperationException if this operator is unsupported for these values (for example
+	 * incompatible or non-numeric types)
+	 */
+	public Value divide(Value value) {
+		throw new UnsupportedValueOperationException(getType(), Operation.DIVIDE);
+	}
+	
+	/**
+	 * Returns a remainder of a division of this value by an argument (operator %).
+	 * 
+	 * @param the right side of the operator
+	 * @return a remainder
+	 * @throws UnsupportedValueOperationException if this operator is unsupported for these values (for example
+	 * incompatible or non-numeric types)
+	 */
+	public Value modulo(Value value) {
+		throw new UnsupportedValueOperationException(getType(), Operation.MODULO);
+	}
+	
+	/**
+	 * Returns a result of a logical and (operator &&).
+	 * 
+	 * @param value the right side of the operator
+	 * @return a conjunction of two values
+	 * @throws UnsupportedValueOperationException if this operator is unsupported for these values (for example
+	 * non-boolean types)
+	 */
+	public Value and(Value value) {
+		throw new UnsupportedValueOperationException(getType(), Operation.AND);
+	}
+	
+	/**
+	 * Returns a result of a logical or (operator ||).
+	 * 
+	 * @param value the right side of the operator
+	 * @return an alternative of two values
+	 * @throws UnsupportedValueOperationException if this operator is unsupported for these values (for example
+	 * non-boolean types)
+	 */
+	public Value or(Value value) {
+		throw new UnsupportedValueOperationException(getType(), Operation.OR);
+	}
+	
+	/**
+	 * Returns a result of applying to this value a regular expression specified as an argument..
+	 * 
+	 * @param value the regular expression
+	 * @return a <code>ValueBoolean</code> representing true if and only if this value matches provided regular
+	 * expression
+	 * @throws UnsupportedValueOperationException if this operator is unsupported for these values
+	 */
+	public Value regExpr(Value value) {
+		throw new UnsupportedValueOperationException(getType(), Operation.REG_EXPR);
+	}
+	
+	/**
+	 * Returns a negation (numeric or logical) of this value. This may refer to operator - or !, depending on type.
+	 * 
+	 * @return a value that is negation of this value
+	 * @throws UnsupportedValueOperationException if this operator is unsupported for this value
+	 */
+	public Value negate() { // !, -
+		throw new UnsupportedValueOperationException(getType(), Operation.NEGATE);
+	}
+	
+	/**
+	 * Returns a size of this value. Semantic depends on type.
+	 * 
+	 * @return a size of this value
+	 * @throws UnsupportedValueOperationException if this operation is unsupported for this value
+	 */
+	public Value valueSize() {
+		// name clash with size from List interface
+		throw new UnsupportedValueOperationException(getType(), Operation.VALUE_SIZE);
+	}
+	
+	/**
+	 * Returns this value converted to another type.
+	 * 
+	 * @param to a desired type
+	 * @return this value converted to the <code>type</code>
+	 * @throws UnsupportedConversionException if a requested conversion is unsupported
+	 */
+	public abstract Value convertTo(Type to);
+	
+	/**
+	 * Returns a textual representation of this value. This method uses conversion to <code>ValueString</code>.
+	 * 
+	 * @return a textual representation of this value
+	 * @see #convertTo(Type)
+	 */
+	@Override
+	public String toString() {
+		return ((ValueString)convertTo(TypePrimitive.STRING)).getValue();
+	}
+	
+	/**
+	 * Returns a default value (such as uninitialized variable). This may be <code>0</code> for integer types,
+	 * <code>false</code> for boolean, <code>null</code> for complex types etc.
+	 * 
+	 * @return a default value of this type
+	 */
+	public abstract Value getDefaultValue();
+}