com.shufudong.GuavaExample.collect.OptionalExample.java Source code

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Here is the source code for com.shufudong.GuavaExample.collect.OptionalExample.java

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/**
 * Copyright 2016 www.xling123.com
 * <p>
 * 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
 * <p>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * 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.shufudong.GuavaExample.collect;

import com.google.common.base.Optional;

import java.util.Set;

/**
 * @author <a href="mailto:shufudong@gmail.com"></a>
 * @ClassName OptionalExample
 * @category Optional
 * @since 2016-05-12
 */
public class OptionalExample {

    public static void main(String[] args) {
        System.out.println(OptionalExample.fromNullable("."));
        System.out.println(OptionalExample.fromNullable(null));
        try {
            OptionalExample.testOptional2();
        } catch (Exception e) {
            e.printStackTrace();
        }
        OptionalExample.testMethodReturn();
    }

    /**
     * @param object
     * @return
     * @category fromNullable?object??
     * ,?fromNullable???
     * @throw
     */
    public static Object fromNullable(Object object) {
        return Optional.fromNullable(object).or("?object,??.");
    }

    /**
     * @return
     * @category <p>??</p>
     * <ol>
     * <li>Optional.of(T)Optional??nullT?T=null</li>
     * <li>Optional.absent()Optional?</li>
     * <li>Optional.fromNullable(T)T?OptionalT???[Optional.fromNullable(null)Optional.absent()</li>
     * </ol>
     * @throw
     */
    public static void testOptional2() throws Exception {
        Optional<Integer> possible = Optional.of(6);
        Optional<Integer> absentOpt = Optional.absent();
        Optional<Integer> NullableOpt = Optional.fromNullable(null);
        Optional<Integer> NoNullableOpt = Optional.fromNullable(10);
        if (possible.isPresent()) {
            System.out.println("possible isPresent:" + possible.isPresent());
            System.out.println("possible value:" + possible.get());
        }
        if (absentOpt.isPresent()) {
            System.out.println("absentOpt isPresent:" + absentOpt.isPresent());
        }
        if (NullableOpt.isPresent()) {
            System.out.println("fromNullableOpt isPresent:" + NullableOpt.isPresent());
        }
        if (NoNullableOpt.isPresent()) {
            System.out.println("NoNullableOpt isPresent:" + NoNullableOpt.isPresent());
        }
    }

    /**
     * @return
     * @category <p></p>
     * <ol>
     * <li> boolean isPresent()Optional?T?nulltrueTnullfalse</li>
     * <li>T get()Optional?TT???nullOptionalget()IllegalStateException</li>
     * <li>T or(T)Optional?T?Optional?T?T</li>
     * <li>T orNull()Optional??TOptional?null?fromNullable()</li>
     * <li>Set<T> asSet()??SetSet?Optional??TSet?T??Optional?T??Set</li>
     * </ol>
     * @throw
     */
    public static void testMethodReturn() {
        Optional<Long> value = method();
        if (value.isPresent() == true) {
            System.out.println(": " + value.get());
        } else {

            System.out.println(": " + value.or(-12L));
        }

        System.out.println(" orNull: " + value.orNull());

        Optional<Long> valueNoNull = methodNoNull();
        if (valueNoNull.isPresent() == true) {
            Set<Long> set = valueNoNull.asSet();
            System.out.println(" set  size : " + set.size());
            System.out.println(": " + valueNoNull.get());
        } else {
            System.out.println(": " + valueNoNull.or(-12L));
        }

        System.out.println(" orNull: " + valueNoNull.orNull());
    }

    private static Optional<Long> method() {
        return Optional.fromNullable(null);
    }

    private static Optional<Long> methodNoNull() {
        return Optional.fromNullable(15L);
    }
}