删除ArrayList对象问题 [英] Removing ArrayList object issue

问题描述

我遇到了在处理赋值时从ArrayList中删除对象的问题
如果我使用normalfor循环，它的工作方式如下

I got an issue with deleting an object from ArrayList when working on the assignment If I use the "normal" for loop, it works as following

public void returnBook(String isbn){        
    for (int i = 0; i < booksBorrowed.size(); i++){            
        if (booksBorrowed.get(i).getISBN() == isbn){
            booksBorrowed.get(i).returnBook();
            booksBorrowed.remove(i);                
        }
    }
}

然而，当我是尝试使用增强的for循环来简化代码，这不起作用并显示java.util.ConcurrentModificationException错误：

However, when I'm trying to simplify the code with enhanced for-loop, that doesn't work and showing java.util.ConcurrentModificationException error:

public void returnBook(String isbn){        
        for (Book book: booksBorrowed){            
            if (book.getISBN() == isbn){
                book.returnBook();
                booksBorrowed.remove(book);                
            }
        }
}

希望你们能照亮我up ..

Hope you guys could lighten me up..

推荐答案

避免ConcurrentModificationException的替代方案是：

Your alternatives to avoid a ConcurrentModificationException are:

List<Book> books = new ArrayList<Book>();
books.add(new Book(new ISBN("0-201-63361-2")));
books.add(new Book(new ISBN("0-201-63361-3")));
books.add(new Book(new ISBN("0-201-63361-4")));

收集您要在增强型for循环中删除的所有记录，并在完成迭代后，删除所有找到的记录。

Collect all the records that you want to delete on enhanced for loop, and after you finish iterating, you remove all found records.

ISBN isbn = new ISBN("0-201-63361-2");
List<Book> found = new ArrayList<Book>();
for(Book book : books){
    if(book.getIsbn().equals(isbn)){
        found.add(book);
    }
}
books.removeAll(found);

或者您可以使用 ListIterator 在迭代过程中支持remove方法。

Or you may use a ListIterator which has support for a remove method during the iteration itself.

ListIterator<Book> iter = books.listIterator();
while(iter.hasNext()){
    if(iter.next().getIsbn().equals(isbn)){
        iter.remove();
    }
}

或者您可以使用第三方库，如< a href =http://code.google.com/p/lambdaj/> LambdaJ ，它会在幕后为您完成所有工作>

Or you may use a third-party library like LambdaJ and it makes all the work for you behind the scenes>

List<Book> filtered = select(books, 
                having(on(Book.class).getIsbn(), 
                        is(new ISBN("0-201-63361-2"))));

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