Java：如何根据条件从数组中删除对象？
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Java: How to remove objects from an Array depending on the condition?
提问by marioosh
I have an array of Objects (file list excatly). How to iterate through this array and delete some Objects (in Java) - depending on the condition ?
我有一个对象数组（文件列表）。如何遍历这个数组并删除一些对象（在 Java 中） - 取决于条件？
File[] files = file.listFiles();
for(File f: files) {
if(someCondition) {
// remove
}
}
回答by Jean Logeart
I think the best Java way to tackle your problem is to convert your array into a list and use an iterator which allows you to remove objects:
我认为解决您的问题的最佳 Java 方法是将您的数组转换为列表并使用允许您删除对象的迭代器：
List<File> files = new ArrayList<File>(Arrays.asList(file.listFiles()));
Iterator<File> iterator = files.iterator();
while(iterator.hasNext()){
File currentFile = iterator.next();
if(someCondition){
iterator.remove();
}
// other operations
}
You can even convert it again into an array if necessary -even though handling a list is probably more convenient ...:
如有必要，您甚至可以将其再次转换为数组 - 即使处理列表可能更方便...：
File[] filesArray = files.toArray();
回答by Alex Gitelman
You may be better off giving FilenameFilter to listFilesand apply condition there. See File documentation http://download.oracle.com/javase/6/docs/api/java/io/File.html
您最好给 FilenameFilterlistFiles并在那里应用条件。请参阅文件文档http://download.oracle.com/javase/6/docs/api/java/io/File.html
回答by Andreas Dolk
We can't deleteelements and resizethe arrays in one step/operation. Arrays can't be resized.
我们无法在一个步骤/操作中删除元素和调整数组大小。数组无法调整大小。
Either use a Listor (1) flag the elements you want to delete and (2) write the elements you want to keep, to a new array.
使用 aList或 (1) 标记要删除的元素并 (2) 将要保留的元素写入新数组。
Here's a solution if you wantto continue with arrays (Listis much easier):
如果您想继续使用数组，这是一个解决方案（List更容易）：
private File[] filter(File[] files) {
boolean[] deleteFlags = new boolean[files.length];
int deleteCounter = 0;
// collection
for (int i = 0; i < files.length; i++) {
if (deleteConditionIsTrue()) {
deleteFlags[i] = true;
deleteCounter++;
}
}
// create result
File[] result = new File[files.length-deleteCounter];
int gapCounter = 0;
for (int i = 0; i < deleteFlags.length; i++) {
if (deleteFlags[i]) {
gapCounter++; // skip entry, has been filtered/deleted
} else {
result[i-gapCounter] = files[i];
}
}
return result;
}
回答by paulsm4
JB Nizet has it exactly right:
JB Nizet 说得完全正确：
You can't "delete" elements from an array
You canset elements to "null". This effectively deletes them (in a C kind of way), but it requires extra logic so you don't accidentally try to reference a null element.
All things being equal, you're probably better off with a List<>, which doesallow you to insert and delete elements.
您不能从数组中“删除”元素
您可以将元素设置为“null”。这有效地删除了它们（以 C 类的方式），但它需要额外的逻辑，因此您不会意外地尝试引用空元素。
所有的事情都是平等的，你可能有过一个更好的名单<>，这也允许你插入和删除元素。
PS: If you know a priori what elements you don't want, the FileFilter idea is an excellent way to keep from getting them in the first place.
PS：如果您事先知道哪些元素是您不想要的，那么 FileFilter 想法是一个很好的方法，可以避免从一开始就获得它们。
回答by JB Nizet
You need to have the index of the object in the array to be able to remove it:
您需要在数组中拥有对象的索引才能将其删除：
File[] files = file.listFiles();
for (int i = 0; i < files.length; i++) {
if(someCondition) {
files[i] = null;
}
}
Note that an array has a fixed length. Removing an element won't shrink the array. If you want this, use a List<File>, iterate through the list using an Iterator, and use the iterator's removemethod to remove the current element.
请注意，数组具有固定长度。删除元素不会缩小数组。如果需要，请使用 a List<File>，使用 an 遍历列表Iterator，并使用迭代器的remove方法删除当前元素。
回答by dbf
I suggest to convert it to list and use LambdaJ filter operation: http://code.google.com/p/lambdaj/wiki/LambdajFeatures. Also filter for lists is available in other libraries, like Guava.
我建议将其转换为列表并使用 LambdaJ 过滤器操作：http: //code.google.com/p/lambdaj/wiki/LambdajFeatures。在其他库中也可以过滤列表，比如 Guava。
