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/*
* Copyright 2006-2012 Amazon Technologies, Inc. or its affiliates.
* Amazon, Amazon.com and Carbonado are trademarks or registered trademarks
* of Amazon Technologies, Inc. or its affiliates. All rights reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.amazon.carbonado.util;
import java.util.Comparator;
import org.cojen.classfile.TypeDesc;
/**
* Compares type conversions, finding the one that is nearest.
*
* @author Brian S O'Neill
* @since 1.2
*/
public class ConversionComparator implements Comparator<Class> {
private final TypeDesc mFrom;
public ConversionComparator(Class fromType) {
mFrom = TypeDesc.forClass(fromType);
}
/**
* Returns true if a coversion is possible to the given type.
*/
public boolean isConversionPossible(Class toType) {
return isConversionPossible(mFrom, TypeDesc.forClass(toType));
}
@SuppressWarnings("unchecked")
private static boolean isConversionPossible(TypeDesc from, TypeDesc to) {
if (from == to) {
return true;
}
if (from.toPrimitiveType() != null && to.toPrimitiveType() != null) {
from = from.toPrimitiveType();
to = to.toPrimitiveType();
} else {
from = from.toObjectType();
to = to.toObjectType();
}
switch (from.getTypeCode()) {
case TypeDesc.OBJECT_CODE: default:
return to.toClass().isAssignableFrom(from.toClass());
case TypeDesc.BOOLEAN_CODE:
return to == TypeDesc.BOOLEAN;
case TypeDesc.BYTE_CODE:
return to == TypeDesc.BYTE || to == TypeDesc.SHORT
|| to == TypeDesc.INT || to == TypeDesc.LONG
|| to == TypeDesc.FLOAT || to == TypeDesc.DOUBLE;
case TypeDesc.SHORT_CODE:
return to == TypeDesc.SHORT
|| to == TypeDesc.INT || to == TypeDesc.LONG
|| to == TypeDesc.FLOAT || to == TypeDesc.DOUBLE;
case TypeDesc.CHAR_CODE:
return to == TypeDesc.CHAR;
case TypeDesc.INT_CODE:
return to == TypeDesc.INT || to == TypeDesc.LONG || to == TypeDesc.DOUBLE;
case TypeDesc.FLOAT_CODE:
return to == TypeDesc.FLOAT || to == TypeDesc.DOUBLE;
case TypeDesc.LONG_CODE:
return to == TypeDesc.LONG;
case TypeDesc.DOUBLE_CODE:
return to == TypeDesc.DOUBLE;
}
}
/**
* Evaluates two types, to see which one is nearest to the from type.
* Return {@literal <0} if "a" is nearest, 0 if both are equally good,
* {@literal >0} if "b" is nearest.
*/
public int compare(Class toType_a, Class toType_b) {
TypeDesc from = mFrom;
TypeDesc a = TypeDesc.forClass(toType_a);
TypeDesc b = TypeDesc.forClass(toType_b);
if (from == a) {
if (from == b) {
return 0;
}
return -1;
} else if (from == b) {
return 1;
}
int result = compare(from, a, b);
if (result != 0) {
return result;
}
if (from.isPrimitive()) {
// Try boxing.
if (from.toObjectType() != null) {
from = from.toObjectType();
return compare(from, a, b);
}
} else {
// Try unboxing.
if (from.toPrimitiveType() != null) {
from = from.toPrimitiveType();
result = compare(from, a, b);
if (result != 0) {
return result;
}
// Try boxing back up. Test by unboxing 'to' types.
if (!toType_a.isPrimitive() && a.toPrimitiveType() != null) {
a = a.toPrimitiveType();
}
if (!toType_b.isPrimitive() && b.toPrimitiveType() != null) {
b = b.toPrimitiveType();
}
return compare(from, a, b);
}
}
return 0;
}
private static int compare(TypeDesc from, TypeDesc a, TypeDesc b) {
if (isConversionPossible(from, a)) {
if (isConversionPossible(from, b)) {
if (from.isPrimitive()) {
if (a.isPrimitive()) {
if (b.isPrimitive()) {
// Choose the one with the least amount of widening.
return primitiveWidth(a) - primitiveWidth(b);
} else {
return -1;
}
} else if (b.isPrimitive()) {
return 1;
}
} else {
// Choose the one with the shortest distance up the class
// hierarchy.
Class fromClass = from.toClass();
if (!fromClass.isInterface()) {
if (a.toClass().isInterface()) {
if (!b.toClass().isInterface()) {
return -1;
}
} else if (b.toClass().isInterface()) {
return 1;
} else {
return distance(fromClass, a.toClass())
- distance(fromClass, b.toClass());
}
}
}
} else {
return -1;
}
} else if (isConversionPossible(from, b)) {
return 1;
}
return 0;
}
// 1 = boolean, 2 = byte, 3 = short, 4 = char, 5 = int, 6 = float, 7 = long, 8 = double
private static int primitiveWidth(TypeDesc type) {
switch (type.getTypeCode()) {
default:
return 0;
case TypeDesc.BOOLEAN_CODE:
return 1;
case TypeDesc.BYTE_CODE:
return 2;
case TypeDesc.SHORT_CODE:
return 3;
case TypeDesc.CHAR_CODE:
return 4;
case TypeDesc.INT_CODE:
return 5;
case TypeDesc.FLOAT_CODE:
return 6;
case TypeDesc.LONG_CODE:
return 7;
case TypeDesc.DOUBLE_CODE:
return 8;
}
}
private static int distance(Class from, Class to) {
int distance = 0;
while (from != to) {
from = from.getSuperclass();
if (from == null) {
return Integer.MAX_VALUE;
}
distance++;
}
return distance;
}
}
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