org.apache.openjpa.meta.InheritanceComparator Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.openjpa.meta;
import java.io.Serializable;
import java.util.Comparator;
/**
* Comparator that keeps classes in inheritance order.
*
* @author Abe White
*/
public class InheritanceComparator
implements Comparator, Serializable {
private static final long serialVersionUID = 1L;
private Class _base = Object.class;
/**
* Set the least-derived type possible; defaults to null.
*/
public void setBase(Class base) {
_base = base;
}
public Class getBase() {
return _base;
}
/**
* Subclasses can override this method to extract the class to compare
* on from the elements of the collection.
*/
protected Class toClass(Object elem) {
return (Class) elem;
}
@Override
public int compare(Object o1, Object o2) {
if (o1 == o2)
return 0;
if (o1 == null)
return -1;
if (o2 == null)
return 1;
Class c1 = toClass(o1);
Class c2 = toClass(o2);
if (c1 == c2)
return 0;
if (c1 == null)
return -1;
if (c2 == null)
return 1;
int i1 = levels(c1);
int i2 = levels(c2);
if (i1 == i2) {
// sort simple interfaces as well as simple order test will fail.
if (c1.isAssignableFrom(c2))
return -1;
if (c2.isAssignableFrom(c1))
return 1;
return c1.getName().compareTo(c2.getName());
}
if (i1 < i2)
return -1;
else if (i1 > i2)
return 1;
else
return 0;
}
/**
* Count the levels of inheritance between this class and our base class.
*/
private int levels(Class to) {
if (to.isInterface())
return to.getInterfaces().length;
for (int i = 0; to != null; i++, to = to.getSuperclass())
if (to == _base)
return i;
return Integer.MAX_VALUE;
}
}