对 Java 集合进行排序

sorting collections java

2022-08-31 11:56:16

我有一个 Java 集合：

Collection<CustomObject> list = new ArrayList<CustomObject>();

CustomObject现在在显示列表之前有一个字段，我想按该排序。idid

我有什么办法可以做到这一点吗？

答案 1

使用比较器：

List<CustomObject> list = new ArrayList<CustomObject>();
Comparator<CustomObject> comparator = new Comparator<CustomObject>() {
    @Override
    public int compare(CustomObject left, CustomObject right) {
        return left.getId() - right.getId(); // use your logic
    }
};

Collections.sort(list, comparator); // use the comparator as much as u want
System.out.println(list);

此外，如果实现，则只需使用CustomObjectComparableCollections.sort(list)

使用JDK 8，语法要简单得多。

List<CustomObject> list = getCustomObjectList();
Collections.sort(list, (left, right) -> left.getId() - right.getId());
System.out.println(list);

更简单

List<CustomObject> list = getCustomObjectList();
list.sort((left, right) -> left.getId() - right.getId());
System.out.println(list);

简单

List<CustomObject> list = getCustomObjectList();
list.sort(Comparator.comparing(CustomObject::getId));
System.out.println(list);

显然，初始代码也可以用于JDK 8。

答案 2

问题是：“排序集合”。所以你不能使用.Collections.sort(List<T> l, Comparator<? super T> comparator)

一些提示：

对于集合类型：

Comparator<String> defaultComparator = new Comparator<String>() {
   @Override
   public int compare(String o1, String o2) {
       return o1.compareTo(o2);
   }
};

Collection<String> collection = getSomeStringCollection();
String[] strings = collection.toArray(new String[collection.size()]);
Arrays.sort(strings, defaultComparator);
List<String> sortedStrings = Arrays.asList(strings);

Collection<String> collection = getSomeStringCollection();
List<String> list = new ArrayList(collection);
Collections.sort(list, defaultComparator);
collection = list; // if you wish

对于列表类型：

List<String> list = getSomeStringList();
Collections.sort(list, defaultComparator);

对于“设置类型”：

Set<String> set = getSomeStringSet();
// Than steps like in 'For Collection type' section or use java.util.TreeSet
// TreeSet sample:
// Sorted using java.lang.Comparable.
Set<String> naturalSorted = new TreeSet(set);

Set<String> set = getSomeStringSet();
Set<String> sortedSet = new TreeSet(defaultComparator);
sortedSet.addAll(set);

Java 8 版本。有java.util.List#sort（Comparator<？ super E> c） 方法

List<String> list = getSomeStringList();
list.sort(defaultComparator);

或

List<String> list = getSomeStringList();
list.sort((String o1, String o2) -> o1.compareTo(o2));

或对于实现可比较的类型：

List<String> list = getSomeStringList();
list.sort(String::compareTo);