01 /*
02 * Java Genetic Algorithm Library (jenetics-1.6.0).
03 * Copyright (c) 2007-2014 Franz Wilhelmstötter
04 *
05 * Licensed under the Apache License, Version 2.0 (the "License");
06 * you may not use this file except in compliance with the License.
07 * You may obtain a copy of the License at
08 *
09 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 *
17 * Author:
18 * Franz Wilhelmstötter (franz.wilhelmstoetter@gmx.at)
19 */
20 package org.jenetics.util;
21
22 import static java.lang.String.format;
23
24 /**
25 * This class is used to <i>tag</i> a class as <i>object</i> with static
26 * methods only. Such classes are not supposed to be treated as <i>types</i>.
27 * The protected constructor always throws an {@link AssertionError} and
28 * prevents the <i>static object</i> from being instantiated.
29 *
30 * The following <i>pattern</i> is used for creating such static helper
31 * classes—the only constructors is declared private to gain the wished
32 * compile-time safety:
33 * [code]
34 * public final class utils extends StaticObject {
35 * private utils() {}
36 *
37 * ...
38 * }
39 * [/code]
40 *
41 * By convention, {@code StaticObject} names are all lower-case in this library.
42 *
43 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
44 * @since 1.1
45 * @version 1.1 — <em>$Date: 2013-09-01 $</em>
46 */
47 public abstract class StaticObject {
48
49 /**
50 * Calling the constructor of an {@code StaticObject} will always throw an
51 * {@link AssertionError}.
52 *
53 * @throws AssertionError always.
54 */
55 protected StaticObject() {
56 String message = "Object instantiation is not allowed";
57
58 final StackTraceElement[] trace = Thread.currentThread().getStackTrace();
59 if (trace.length >= 3) {
60 message = format(
61 "Instantiation of '%s' is not allowed.",
62 trace[2].getClassName()
63 );
64 }
65
66 throw new AssertionError(message);
67 }
68
69 }
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