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Java example source code file (UniqueAnnotations.java)

This example Java source code file (UniqueAnnotations.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

annotation, atomicinteger, bindingannotation, class, internal, override, retention, string, uniqueannotations

The UniqueAnnotations.java Java example source code

 * Copyright (C) 2008 Google Inc.
 * 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,
 * See the License for the specific language governing permissions and
 * limitations under the License.

package com.google.inject.internal;

import static java.lang.annotation.RetentionPolicy.RUNTIME;

import com.google.inject.BindingAnnotation;

import java.lang.annotation.Annotation;
import java.lang.annotation.Retention;
import java.util.concurrent.atomic.AtomicInteger;

 * @author jessewilson@google.com (Jesse Wilson)
public class UniqueAnnotations {
  private UniqueAnnotations() {}
  private static final AtomicInteger nextUniqueValue = new AtomicInteger(1);

   * Returns an annotation instance that is not equal to any other annotation
   * instances, for use in creating distinct {@link com.google.inject.Key}s.
  public static Annotation create() {
    return create(nextUniqueValue.getAndIncrement());

  static Annotation create(final int value) {
    return new Internal() {
      public int value() {
        return value;

      public Class<? extends Annotation> annotationType() {
        return Internal.class;

      @Override public String toString() {
        return "@" + Internal.class.getName() + "(value=" + value + ")";

      @Override public boolean equals(Object o) {
        return o instanceof Internal
            && ((Internal) o).value() == value();

      @Override public int hashCode() {
        return (127 * "value".hashCode()) ^ value;

  @Retention(RUNTIME) @BindingAnnotation
  @interface Internal {
    int value();

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