如何獲取ArrayList的最後一個值

本文翻譯自：How to get the last value of an ArrayList

How can I get the last value of an ArrayList? 如何獲取ArrayList的最後一個值？

I don't know the last index of the ArrayList. 我不知道ArrayList的最後一個索引。

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#1樓

參考：https://stackoom.com/question/2sw5/如何獲取ArrayList的最後一個值

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#2樓

There isn't an elegant way in vanilla Java. 在香草Java中沒有一種優雅的方式。

Google Guava 谷歌番石榴

The Google Guava library is great - check out their Iterables class . Google Guava庫很棒 - 查看他們的Iterables類 。 This method will throw a NoSuchElementException if the list is empty, as opposed to an IndexOutOfBoundsException , as with the typical size()-1 approach - I find a NoSuchElementException much nicer, or the ability to specify a default: 如果列表爲空，此方法將拋出NoSuchElementException ，而不是IndexOutOfBoundsException ，與典型的size()-1方法一樣 - 我發現NoSuchElementException更好，或者指定默認值的能力：

lastElement = Iterables.getLast(iterableList);

You can also provide a default value if the list is empty, instead of an exception: 如果列表爲空，您還可以提供默認值，而不是例外：

lastElement = Iterables.getLast(iterableList, null);

or, if you're using Options: 或者，如果您使用選項：

lastElementRaw = Iterables.getLast(iterableList, null);
lastElement = (lastElementRaw == null) ? Option.none() : Option.some(lastElementRaw);

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#3樓

I use micro-util class for getting last (and first) element of list: 我使用micro-util類來獲取列表的最後一個（和第一個）元素：

public final class Lists {

    private Lists() {
    }

    public static <T> T getFirst(List<T> list) {
        return list != null && !list.isEmpty() ? list.get(0) : null;
    }

    public static <T> T getLast(List<T> list) {
        return list != null && !list.isEmpty() ? list.get(list.size() - 1) : null;
    }
}

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Slightly more flexible: 稍微靈活一點：

import java.util.List;

/**
 * Convenience class that provides a clearer API for obtaining list elements.
 */
public final class Lists {

  private Lists() {
  }

  /**
   * Returns the first item in the given list, or null if not found.
   *
   * @param <T> The generic list type.
   * @param list The list that may have a first item.
   *
   * @return null if the list is null or there is no first item.
   */
  public static <T> T getFirst( final List<T> list ) {
    return getFirst( list, null );
  }

  /**
   * Returns the last item in the given list, or null if not found.
   *
   * @param <T> The generic list type.
   * @param list The list that may have a last item.
   *
   * @return null if the list is null or there is no last item.
   */
  public static <T> T getLast( final List<T> list ) {
    return getLast( list, null );
  }

  /**
   * Returns the first item in the given list, or t if not found.
   *
   * @param <T> The generic list type.
   * @param list The list that may have a first item.
   * @param t The default return value.
   *
   * @return null if the list is null or there is no first item.
   */
  public static <T> T getFirst( final List<T> list, final T t ) {
    return isEmpty( list ) ? t : list.get( 0 );
  }

  /**
   * Returns the last item in the given list, or t if not found.
   *
   * @param <T> The generic list type.
   * @param list The list that may have a last item.
   * @param t The default return value.
   *
   * @return null if the list is null or there is no last item.
   */
  public static <T> T getLast( final List<T> list, final T t ) {
    return isEmpty( list ) ? t : list.get( list.size() - 1 );
  }

  /**
   * Returns true if the given list is null or empty.
   *
   * @param <T> The generic list type.
   * @param list The list that has a last item.
   *
   * @return true The list is empty.
   */
  public static <T> boolean isEmpty( final List<T> list ) {
    return list == null || list.isEmpty();
  }
}

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#4樓

如果可以，可以將ArrayList替換爲ArrayDeque ，它具有removeLast等方便的方法。

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#5樓

How about this.. Somewhere in your class... 怎麼樣......你班上的某個地方......

List<E> list = new ArrayList<E>();
private int i = -1;
    public void addObjToList(E elt){
        i++;
        list.add(elt);
    }


    public E getObjFromList(){
        if(i == -1){ 
            //If list is empty handle the way you would like to... I am returning a null object
            return null; // or throw an exception
        }

        E object = list.get(i);
        list.remove(i); //Optional - makes list work like a stack
        i--;            //Optional - makes list work like a stack
        return object;
    }

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#6樓

The last item in the list is list.size() - 1 . 列表中的最後一項是list.size() - 1 。 The collection is backed by an array and arrays start at index 0. 該集合由數組支持，數組從索引0開始。

So element 1 in the list is at index 0 in the array 因此列表中的元素1位於數組中的索引0處

Element 2 in the list is at index 1 in the array 列表中的元素2位於數組中的索引1處

Element 3 in the list is at index 2 in the array 列表中的元素3位於數組中的索引2處

and so on.. 等等..