| /* |
| * Copyright 2000-2009 JetBrains s.r.o. |
| * |
| * 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.intellij.openapi.util; |
| |
| import org.jetbrains.annotations.NotNull; |
| import org.jetbrains.annotations.Nullable; |
| |
| /** |
| * @author dsl |
| */ |
| public interface Computable <T> { |
| |
| T compute(); |
| |
| class PredefinedValueComputable<T> implements Computable<T> { |
| |
| private final T myValue; |
| |
| public PredefinedValueComputable(@Nullable T value) { |
| myValue = value; |
| } |
| |
| @Override |
| public T compute() { |
| return myValue; |
| } |
| } |
| |
| abstract class NotNullCachedComputable<T> implements Computable<T> { |
| private T myValue; |
| |
| @NotNull |
| protected abstract T internalCompute(); |
| |
| @NotNull |
| @Override |
| public final T compute() { |
| if (myValue == null) { |
| myValue = internalCompute(); |
| } |
| return myValue; |
| } |
| } |
| |
| abstract class NullableCachedComputable<T> implements Computable<T> { |
| private static final Object NULL_VALUE = new Object(); |
| private Object myValue; |
| |
| @Nullable |
| protected abstract T internalCompute(); |
| |
| @Nullable |
| @Override |
| public final T compute() { |
| if (myValue == null) { |
| final T value = internalCompute(); |
| myValue = value != null ? value : NULL_VALUE; |
| } |
| return myValue != NULL_VALUE ? (T)myValue : null; |
| } |
| } |
| } |