如何编写比较器以将列表的所有元素与输入进行比较并移动到顶部

Question

我有一个列表

List<String> myList = Arrays.asList("1234", "1214", "1334");

我的输入是:

String mInput = "1214"

如何写一个比较器来比较myList和mInput的所有元素，如果相等，则将其移动到列表的顶部

Answer 1

您不需要可以使用的比较器：

List<String> myList = new ArrayList<>(Arrays.asList("1234", "1214", "1334"));
String mInput = "1214";
if (myList.contains(mInput)) {
    myList.remove(mInput);// remove mInput 
    myList.add(0, mInput);// add it to to index 0 (top of list)
}
System.out.println(myList);// Input [1214, 1234, 1334]

注意你必须使用new ArrayList<>(Arrays.asList("1234", "1214", "1334"))来理解为什么，你可以阅读这个UnsupportedOperationException when trying to remove from the list returned by Array.asList

Answer 2

如果你真的需要这里的比较器，你可以这样做（假设mInput不是null）：
myList.sort((String o1, String o2) -> mInput.equals(o1) && !mInput.equals(o2) ? -1 : o1.compareTo(o2));

Answer 3

你可以自己写Comparator:

class BringToFrontComparator<T extends Comparable<T>> implements Comparator<T> {
    T front;

    public BringToFrontComparator(T front) {
        this.front = front;
    }

    @Override
    public int compare(T o1, T o2) {
        return o1.equals(front) && !o2.equals(front)
                // Front one is always less than anything other than itself.
                ? -1
                // Normal comparison elsewhere.
                : o1.compareTo(o2);
    }
}

public void test(String[] args) throws Exception {
    List<String> myList = Arrays.asList("1234", "1214", "1334");
    String mInput = "1334";
    Collections.sort(myList, new BringToFrontComparator<>(mInput));
    System.out.println(myList);
}

打印

[1334, 1214, 1234]

如何编写比较器以将列表的所有元素与输入进行比较并移动到顶部

How to write a comparator to compare all the elements of a list to a input and move to top

java

arraylist

comparator