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/*
* esodata - data structures and other things, of varying utility
* Copyright 2022, Ben Culkin
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
package bjc.data;
import java.util.*;
/**
* Utility methods for dealing with contexts.
*
* @author Ben Culkin
*
*/
public class Contexts {
/**
* The null context, which always throws an exception.
*/
public static final Context NULL = new NullContextImpl();
private Contexts() {
throw new UnsupportedOperationException();
}
/**
* Create a new context with no parent.
*
* @return A context with no parent.
*/
public static Context create() {
return new ContextImpl(NULL);
}
/**
* Create a context with the specified parent.
*
* @param parent The parent of this context.
*
* @return A context with the given context as its parent.
*/
public static Context create(Context parent) {
return new ContextImpl(parent);
}
}
class NullContextImpl implements Context {
@Override
public Context getParent() {
return this;
}
@Override
public void register(String name, Object o) {
throw new UnsupportedOperationException();
}
@Override
public Object get(String name) {
throw new NoSuchElementException();
}
@Override
public <T> T get(Class<T> contract) {
throw new NoSuchElementException();
}
}
class ContextImpl implements Context {
private final Context parent;
private final Map<String, Object> objects;
public ContextImpl(Context parent) {
this.parent = parent;
this.objects = new HashMap<>();
}
@Override
public void register(String name, Object o) {
objects.put(name, o);
}
@Override
public Object get(String name) {
if (objects.containsKey(name)) {
return objects.get(name);
}
return parent.get(name);
}
@SuppressWarnings("unchecked")
@Override
public <T> T get(Class<T> contract) {
for (Object o : objects.values()) {
if (contract.isInstance(o)) {
return (T) o;
}
}
return parent.get(contract);
}
@Override
public Context getParent() {
return parent;
}
}
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