Java 8 bekommt auch eine Optional-Klasse (wie Guava und Scala)

+/*

+ * Copyright (c) 2012, Oracle and/or its affiliates. All rights reserved.

+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

+ *

+ * This code is free software; you can redistribute it and/or modify it

+ * under the terms of the GNU General Public License version 2 only, as

+ * published by the Free Software Foundation. Oracle designates this

+ * particular file as subject to the "Classpath" exception as provided

+ * by Oracle in the LICENSE file that accompanied this code.

+ *

+ * This code 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

+ * version 2 for more details (a copy is included in the LICENSE file that

+ * accompanied this code).

+ *

+ * You should have received a copy of the GNU General Public License version

+ * 2 along with this work; if not, write to the Free Software Foundation,

+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

+ *

+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

+ * or visit www.oracle.com if you need additional information or have any

+ * questions.

+ */

+package java.util;

+

+import java.util.functions.Factory;

+import java.util.functions.Mapper;

+

+/**

+ * Optional

+ *

+ * @author Brian Goetz

+ */

+public class Optional<T> {

+ private final static Optional<?> EMPTY = new Optional<>();

+

+ private final T value;

+ private final boolean present;

+

+ public Optional(T value) {

+ this.value = value;

+ this.present = true;

+ }

+

+ private Optional() {

+ this.value = null;

+ this.present = false;

+ }

+

+ public static<T> Optional<T> empty() {

+ return (Optional<T>) EMPTY;

+ }

+

+ public T get() {

+ if (!present)

+ throw new NoSuchElementException();

+ return value;

+ }

+

+ public boolean isPresent() {

+ return present;

+ }

+

+ public T orElse(T other) {

+ return present ? value : other;

+ }

+

+ public T orElse(Factory<T> other) {

+ return present ? value : other.make();

+ }

+

+ public<V extends Throwable> T orElseThrow(Factory<V> exceptionFactory) throws V {

+ if (present)

+ return value;

+ else

+ throw exceptionFactory.make();

+ }

+

+ public<V extends Throwable> T orElseThrow(Class<V> exceptionClass) throws V {

+ if (present)

+ return value;

+ else

+ try {

+ throw exceptionClass.newInstance();

+ }

+ catch (InstantiationException | IllegalAccessException e) {

+ throw new IllegalStateException("Unexpected exception: " + e, e);

+ }

+ }

+

+ public<V> Optional<V> map(Mapper<T, V> mapper) {

+ return present ? new Optional<>(mapper.map(value)) : Optional.<V>empty();

+ }

+

+ @Override

+ public boolean equals(Object o) {

+ if (this == o) return true;

+ if (o == null || getClass() != o.getClass()) return false;

+

+ Optional optional = (Optional) o;

+

+ if (present != optional.present) return false;

+ if (value != null ? !value.equals(optional.value) : optional.value != null) return false;

+

+ return true;

+ }

+

+ @Override

+ public int hashCode() {

+ int result = value != null ? value.hashCode() : 0;

+ result = 31 * result + (present ? 1 : 0);

+ return result;

+ }

+}


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