我發(fā)現(xiàn)使用基于Java的應(yīng)用程序時(shí)， 裝飾器和適配器有時(shí)會(huì)很有用。 這些“包裝器”在各種情況下都能很好地工作，并且相當(dāng)容易理解和實(shí)現(xiàn)，但是當(dāng)需要包裝對(duì)象的層次結(jié)構(gòu)而不是單個(gè)對(duì)象時(shí)，事情可能會(huì)變得有些棘手。 在這篇博客文章中，我研究了Java 8流如何使在對(duì)象集合和包裝這些對(duì)象的對(duì)象集合之間轉(zhuǎn)換變得更加容易。

在此討論中，我將應(yīng)用兩個(gè)簡(jiǎn)單的Java類，分別表示Movie類和“包裝”該類的類MovieWrapper 。 我在有關(guān)Java集合的JDK 8增強(qiáng)功能的 帖子中使用了Movie類。 接下來(lái)顯示Movie類和包裝它的類。

電影.java

package dustin.examples.jdk8.streams;import java.util.Objects;/*** Basic characteristics of a motion picture.** @author Dustin*/ public class Movie {/** Title of movie. */private final String title;/** Year of movie's release. */private final int yearReleased;/** Movie genre. */private final Genre genre;/** MPAA Rating. */private final MpaaRating mpaaRating;/** imdb.com Rating. */private final int imdbTopRating;public Movie(final String newTitle, final int newYearReleased,final Genre newGenre, final MpaaRating newMpaaRating,final int newImdbTopRating){this.title = newTitle;this.yearReleased = newYearReleased;this.genre = newGenre;this.mpaaRating = newMpaaRating;this.imdbTopRating = newImdbTopRating;}public String getTitle(){return this.title;}public int getYearReleased(){return this.yearReleased;}public Genre getGenre(){return this.genre;}public MpaaRating getMpaaRating(){return this.mpaaRating;}public int getImdbTopRating(){return this.imdbTopRating;}@Overridepublic boolean equals(Object other){if (!(other instanceof Movie)){return false;}final Movie otherMovie = (Movie) other;return Objects.equals(this.title, otherMovie.title)&& Objects.equals(this.yearReleased, otherMovie.yearReleased)&& Objects.equals(this.genre, otherMovie.genre)&& Objects.equals(this.mpaaRating, otherMovie.mpaaRating)&& Objects.equals(this.imdbTopRating, otherMovie.imdbTopRating);}@Overridepublic int hashCode(){return Objects.hash(this.title, this.yearReleased, this.genre, this.mpaaRating, this.imdbTopRating);}@Overridepublic String toString(){return "Movie: " + this.title + " (" + this.yearReleased + "), " + this.genre + ", " + this.mpaaRating + ", "+ this.imdbTopRating;} }

MovieWrapper.java

package dustin.examples.jdk8.streams;/*** Wraps a movie like a Decorator or Adapter might.* * @author Dustin*/ public class MovieWrapper {private Movie wrappedMovie;public MovieWrapper(final Movie newMovie){this.wrappedMovie = newMovie;}public Movie getWrappedMovie(){return this.wrappedMovie;}public void setWrappedMovie(final Movie newMovie){this.wrappedMovie = newMovie;}public String getTitle(){return this.wrappedMovie.getTitle();}public int getYearReleased(){return this.wrappedMovie.getYearReleased();}public Genre getGenre(){return this.wrappedMovie.getGenre();}public MpaaRating getMpaaRating(){return this.wrappedMovie.getMpaaRating();}public int getImdbTopRating(){return this.wrappedMovie.getImdbTopRating();}@Overridepublic String toString(){return this.wrappedMovie.toString();} }

通過(guò)上面定義的Movie和MovieWrapper類，我現(xiàn)在看一下將其中一個(gè)的集合轉(zhuǎn)換為另一個(gè)的集合。 在JDK 8之前，將Movie對(duì)象的集合轉(zhuǎn)換為MovieWrapper對(duì)象的集合的典型方法是迭代Movie對(duì)象的源集合，并將每個(gè)對(duì)象添加到MovieWrapper對(duì)象的新集合中。 下一個(gè)代碼清單對(duì)此進(jìn)行了演示。

將包裝對(duì)象的集合轉(zhuǎn)換為包裝對(duì)象的集合

// movies previously defined as Set<Movie> final Set<MovieWrapper> wrappedMovies1 = new HashSet<>(); for (final Movie movie : movies) {wrappedMovies1.add(new MovieWrapper(movie)); }

使用JDK 8流，現(xiàn)在可以如下面的代碼清單所示實(shí)現(xiàn)上述操作。

將包裝對(duì)象的集合轉(zhuǎn)換為包裝對(duì)象的集合– JDK 8

// movies previously defined as Set<Movie> final Set<MovieWrapper> wrappedMovies2 =movies.stream().map(movie -> new MovieWrapper(movie)).collect(Collectors.toSet());

可以類似地比較轉(zhuǎn)換另一個(gè)方向（從包裝對(duì)象的集合到包裝對(duì)象的集合），以演示JDK 8如何改變這一方向。 接下來(lái)的兩個(gè)代碼清單顯示了舊方法和JDK 8方法。

將包裝對(duì)象的集合轉(zhuǎn)換為包裝對(duì)象的集合

final Set<Movie> newMovies1 = new HashSet(); for (final MovieWrapper wrappedMovie : wrappedMovies1) {newMovies1.add(wrappedMovie.getWrappedMovie()); }

將包裝對(duì)象的集合轉(zhuǎn)換為包裝對(duì)象的集合– JDK 8

final Set<Movie> newMovies2 =wrappedMovies2.stream().map(MovieWrapper::getWrappedMovie).collect(Collectors.toSet());

就像我在JDK 8中的“流支持集合功能”一文中的一些示例一樣，本文中的示例展示了JDK 8中提供的聚合操作的強(qiáng)大功能。這些聚合操作相對(duì)于傳統(tǒng)迭代的優(yōu)勢(shì)包括代碼中的簡(jiǎn)潔性，可以說(shuō)是（也許最終）更大的可讀性，以及內(nèi)部迭代的優(yōu)勢(shì)（包括更容易的潛在流支持的并行化）。 Java 8將轉(zhuǎn)換對(duì)象轉(zhuǎn)換為另一種類型，顯示了使用流和更復(fù)雜的Function在不太相關(guān)的對(duì)象的集合之間進(jìn)行轉(zhuǎn)換的一個(gè)很好的示例。

翻譯自: https://www.javacodegeeks.com/2015/02/using-jdk-8-streams-convert-collections-wrapped-objects-collections-wrapper-objects.html

總結(jié)

以上是生活随笔為你收集整理的使用JDK 8流在包装对象的集合和包装对象的集合之间转换的全部?jī)?nèi)容，希望文章能夠幫你解決所遇到的問(wèn)題。

如果覺(jué)得生活随笔網(wǎng)站內(nèi)容還不錯(cuò)，歡迎將生活随笔推薦給好友。