我怎样才能使我的类迭代，所以我可以使用foreach语法？ [英] How can I make my class iterable so I can use foreach syntax?

问题描述

我有 Book 和 BookList 类。 BookList 就像这样：

  public class BookList 
 {
 private final List< Book> bList = new ArrayList< Book>（）; 
 
 public int size（）{return bList.size（）; } 
 
 public boolean isEmpty（）{...} 
 
 public boolean contains（Book b）{...} 
 
 public boolean add （Book b）{...} 
 
 public boolean remove（Book b）{..} 
 
 public void clear（）{...} 
 
 public Object get（int index）{...} 
 
 $ b $ / code> 

在我的主类中，我想要在每个循环中打印书籍的标题：



  for（Book b ：bList）
 {
 b.print（）; 
 
 $ / code 
 
 
 
 Eclipse说：
 
 < blockquote> 
 
只能遍历数组或java.lang.Iterable的实例 
 
得到这个工作吗？
解决方案
您需要实现  Iterable  界面，这意味着您需要实现迭代器（）方法。在你的情况下，这可能看起来像这样：
  public class BookList implements Iterable< Book> {
 private final List< Book> bList = new ArrayList< Book>（）; 
 
 @Override 
 public Iterator< Book> iterator（）{
 return bList.iterator（）; 
} 
 
 ... 
} 
  
 
I have Book and BookList classes. BookList is something like this:
public class BookList 
{
    private final List<Book> bList = new ArrayList<Book>();

    public int size() { return bList.size(); }

    public boolean isEmpty() {  ... }

    public boolean contains(Book b) { ...  }

    public boolean add(Book b) { ...  }

    public boolean remove(Book b) {  .. } 

    public void clear() { ... }

    public Object get(int index) { ... }

}
In my main class I want to print titles of books with in a for each loop:
for(Book b : bList)
{
    b.print();
}
Eclipse says: 

  
Can only iterate over an array or an instance of java.lang.Iterable
How can I get this working?
解决方案
You need to implement the Iterable interface, which means you need to implement the iterator() method. In your case, this might look something like this:
public class BookList implements Iterable<Book> {
    private final List<Book> bList = new ArrayList<Book>();

    @Override
    public Iterator<Book> iterator() {
        return bList.iterator();
    }

    ...
}


                        
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