在列表的末尾放置null [英] Placing null at the end of the List

问题描述

我需要将空对象放在 List 的末尾。下面是我为此目的所做的一个例子：

I have a need to place null objects at the end of the List. Here is a sample what I have done for this purpose:

public static void main(String... args) {
    List<String> strings = Arrays.asList(new String[]{"A", null, "B"});

    for(String string : strings) {
        System.out.println(string);
    }

    System.out.println("==================");

    List<String> result = new ArrayList<String>();
    List<String> nullStrings = new ArrayList<String>();

    for(String string : strings) {
        if(string != null) {
            result.add(string);         
        } else {
            nullStrings.add(string);
        }
    }

    result.addAll(nullStrings);

    for(String string : result) {
        System.out.println(string);
    }
}

我期待着更高效，去做这个。是否可以在实际列表内部交换，以便将null节点放置在末尾，这样我不需要另外两个列表（nullStrings，result）和额外的迭代。

I am looking forward to a more efficient and intelligent way to do this. Is it possible to swap inside the actual list so that null node get placed at the end, so that I don't need the other two list(nullStrings, result) and extra iteration.

排序不适用于我的案例。这个示例代码我只是为了测试目的。其实我有一个不同类型的对象。

Sorting will not work for my case. This sample code I made just for testing purpose. Actually I have a different type of Object. Also Sorting will break the position.

说我有这个 null，Obj2，Obj1 ，如果做任何排序它可能发生 Obj1，Obj2，null 。但我需要 Obj2，Obj1，null 。

Say I have this null, Obj2, Obj1, if do anything like sorting it may happens Obj1, Obj2, null. But I need Obj2, Obj1, null.

推荐答案

它使用 Collections.sort 和自定义 Comparator 。

这里的比较代码：

@Override 
public int compare(String left, String right) {
 if (left == right) {
   return 0;
 }
 if (left == null) {
   return 1;
 }
 if (right == null) {
   return -1;
 }
 return 0;
 }

请注意，根据 Comparator 将不会重新排序。从 Collections.sort ：

Note that elements that have an equal value according to this Comparator won't be re-ordered. From Collections.sort:

：等于元素将不会作为排序的结果重新排序。

This sort is guaranteed to be stable: equal elements will not be reordered as a result of the sort.

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