org.apache.logging.log4j.util.Lazy 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.logging.log4j.util;
import java.util.Objects;
import java.util.function.Function;
import java.util.function.Supplier;
/**
* Provides a lazily-initialized value from a {@code Supplier}.
*
* @param type of value
*/
public interface Lazy extends Supplier {
/**
* Returns the value held by this lazy. This may cause the value to initialize if it hasn't been already.
*/
T value();
/**
* Returns the value held by this lazy. This may cause the value to initialize if it hasn't been already.
*/
@Override
default T get() {
return value();
}
/**
* Creates a new lazy value derived from this lazy value using the provided value mapping function.
*/
default Lazy map(final Function function) {
return lazy(() -> function.apply(value()));
}
/**
* Indicates whether this lazy value has been initialized.
*/
boolean isInitialized();
/**
* Sets this lazy value to the provided value.
*
* @throws UnsupportedOperationException if this type of lazy value cannot be updated
*/
void set(final T newValue);
/**
* Creates a strict lazy value using the provided Supplier. The supplier is guaranteed to only be invoked by at
* most one thread, and all threads will see the same published value when this returns.
*/
static Lazy lazy(final Supplier supplier) {
Objects.requireNonNull(supplier);
return new LazyUtil.SafeLazy<>(supplier);
}
/**
* Creates a lazy value using the provided constant value.
*/
static Lazy value(final T value) {
return new LazyUtil.Constant<>(value);
}
/**
* Creates a lazy value using a weak reference to the provided value.
*/
static Lazy weak(final T value) {
return new LazyUtil.WeakConstant<>(value);
}
/**
* Creates a pure lazy value using the provided Supplier to initialize the value. The supplier may be invoked more
* than once, and the return value should be a purely computed value as the result may be a different instance
* each time. This is useful for building cache tables and other pure computations.
*/
static Lazy pure(final Supplier supplier) {
Objects.requireNonNull(supplier);
return new LazyUtil.PureLazy<>(supplier);
}
}