Java 8类数组的数组流转换
我不熟悉Java8。我需要使用以下方法在Java 8中创建字符串数组: 我拥有如下所述的学校、学科、出版商和书籍的POJO-Java 8类数组的数组流转换,java,java-8,java-stream,collectors,Java,Java 8,Java Stream,Collectors,我不熟悉Java8。我需要使用以下方法在Java 8中创建字符串数组: 我拥有如下所述的学校、学科、出版商和书籍的POJO- public class School { private Subject[] subjects; public Subject[] getSubjects() { return subjects; } public void setSubjects(Subject[] subjects) { thi
public class School {
private Subject[] subjects;
public Subject[] getSubjects() {
return subjects;
}
public void setSubjects(Subject[] subjects) {
this.subjects = subjects;
}
}
public class Subject {
private String subjectName;
private String subjectId;
private Publisher publisher;
public String getSubjectName() {
return subjectName;
}
public void setSubjectName(String subjectName) {
this.subjectName = subjectName;
}
public String getSubjectId() {
return subjectId;
}
public void setSubjectId(String subjectId) {
this.subjectId = subjectId;
}
public Publisher getpublisher() {
return publisher;
}
public void setPublisher(Publisher publisher) {
this.publisher = publisher;
}
}
public class Publisher{
private String name;
private String sinNo;
private Book[] books;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSinNo() {
return sinNo;
}
public void setSinNo(String sinNo) {
this.sinNo = sinNo;
}
public Book[] getBooks() {
return books;
}
public void setBooks(Book[] books) {
this.books = books;
}
}
public class Book {
private String bookName;
private String bookId;
public String getBookName() {
return bookName;
}
public void setBookName(String bookName) {
this.bookName = bookName;
}
public String getBookId() {
return bookId;
}
public void setBookId(String bookId) {
this.bookId = bookId;
}
}
现在,我的任务是创建一个数组,其中包含我拥有的学校对象的所有bookid。下面的旧java代码是必需的代码
public static void main(String[] args) {
List<String> list = new ArrayList<>();
School first = <<School Object>>;
for(Subject sub : first.getSubjects()){
Publisher p = sub.getpublisher();
for(Book b : p.getBooks()) {
list.add(b.getBookId());
}
}
//desired result
String[] bookIds = (String[]) list.toArray();
}
publicstaticvoidmain(字符串[]args){
列表=新的ArrayList();
学校优先=;
for(Subject sub:first.getSubjects()){
Publisher p=sub.getpublisher();
for(Book b:p.getBooks()){
添加(b.getBookId());
}
}
//期望结果
String[]bookIds=(String[])list.toArray();
}
}
这可以通过Java8流、收集器和映射来实现吗?
另外,如果我们只想得到那些奇数/偶数的图书ID 是的,你需要一个团队来实现这一点
Stream.of(first.getSubjects())
.map(Subject::getPublisher)
.map(Publisher::getBooks)
.flatMap(Arrays::stream)
.map(Book::getBookId)
.collect(Collectors.toList());
如果你想让它空安全,你需要添加额外的过滤,如
List<String> collect = Stream.of(first.getSubjects())
.map(Subject::getPublisher)
.filter(Objects::nonNull) // filter all null publishers
.map(Publisher::getBooks)
.filter(Objects::nonNull) // filter all null book lists
.flatMap(Arrays::stream)
.map(Book::getBookId)
.filter(Objects::nonNull) // filter all null book ids
.collect(Collectors.toList());
List collect=Stream.of(first.getSubjects())
.map(主题::getPublisher)
.filter(Objects::nonNull)//筛选所有空发布服务器
.map(Publisher::getBooks)
.filter(Objects::nonNull)//筛选所有空的图书列表
.flatMap(数组::流)
.map(Book::getBookId)
.filter(Objects::nonNull)//筛选所有空的图书ID
.collect(Collectors.toList());
Yes,first.getSubjects(),stream,map,map,flatMap,map,collect:)我建议您使用List
s而不是数组。谢谢,另外,如果我们只想得到奇偶图书ID,在m.antkowicz的回答中,您可能会得到duplucate ID,如果您想遵守这种情况,那么您应该添加distinct()在收集项目之前。只需在将项目收集到列表之前添加适当的过滤器
。我还将使用数组.stream
来初始创建流,而不是stream.of
。