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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;
import pl.edu.mimuw.cloudatlas.model.ValueNull;
/**
* A special null value of an unknown type. This class is a singleton.
*
* @see TypePrimitve#NULL
* @see Type#isCompatible(Value)
*/
public class ValueNull extends Value {
private static ValueNull instance = null;
private ValueNull() {}
/**
* Gets a singleton instance of the <code>ValueNull</code> class. Every call to this method returns the same
* reference.
*
* @return an instance of <code>ValueNull</code>
*/
public static ValueNull getInstance() {
if(instance == null)
instance = new ValueNull();
return instance;
}
@Override
public Value getDefaultValue() {
return instance;
}
@Override
public Value convertTo(Type type) {
switch(type.getPrimaryType()) {
case STRING:
return ValueString.NULL_STRING;
default:
return this;
}
}
@Override
public Type getType() {
return TypePrimitive.NULL;
}
@Override
public boolean isNull() {
return true;
}
@Override
public Value isEqual(Value value) {
return new ValueBoolean(isNull() && value.isNull());
}
@Override
public Value isLowerThan(Value value) {
if(value == getInstance())
return this;
return value.isLowerThan(this);
}
@Override
public Value addValue(Value value) {
if(value == getInstance())
return this;
return value.addValue(this);
}
@Override
public Value subtract(Value value) {
if(value == getInstance())
return this;
return value.subtract(this);
}
@Override
public Value multiply(Value value) {
if(value == getInstance())
return this;
return value.multiply(this);
}
@Override
public Value divide(Value value) {
if(value == getInstance())
return this;
return value.divide(this);
}
@Override
public Value modulo(Value value) {
if(value == getInstance())
return this;
return value.modulo(this);
}
@Override
public Value and(Value value) {
if(value == getInstance())
return this;
return value.and(this);
}
@Override
public Value or(Value value) {
if(value == getInstance())
return this;
return value.or(this);
}
@Override
public Value regExpr(Value value) {
if(value == getInstance())
return this;
return value.regExpr(this);
}
@Override
public Value negate() {
return this;
}
@Override
public Value valueSize() {
return this;
}
}
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