Question

import java.util.*;

class MyComp implements Comparator<String>{
    public int compare(String aStr, String bStr) {
        return bStr.compareTo(aStr);
    }
}


public class CustomComparatorTest {

    public static void main(String[] args) {

        MyComp my = new MyComp();
        TreeSet<String> ts = new TreeSet<String>(my);
        ts.add("C");
        ts.add("A");
        ts.add("B");
        ts.add("Y");
        ts.add("T");
        ts.add("W");

        for(String element : ts)
        {
            System.out.println(element + " ");
        }
        System.out.println();
    }
}

Answer 1

假设你问的是如何在没有在main方法中显式调用的情况下执行compare方法，每次向其添加元素时都会通过TreeSet代码调用它，以便在TreeSet应该存储元素。这种方式TreeSet维护元素按照您传递给构造函数的Comparator所规定的顺序排序。

Answer 2

public boolean add(E e) {return m.put(e, PRESENT)==null;}

当你调用 add（x）函数时，在TreeSet中调用 TreeMap.put（）方法，在 TreeMap.put（）中，它将调用比较器。像这样的源代码：

public V put(K key, V value) {
        Entry<K,V> t = root;
        if (t == null) {
            compare(key, key); // type (and possibly null) check

            root = new Entry<>(key, value, null);
            size = 1;
            modCount++;
            return null;
        }
        int cmp;
        Entry<K,V> parent;
        // split comparator and comparable paths
        Comparator<? super K> cpr = comparator;
        if (cpr != null) {
            do {
                parent = t;
                cmp = cpr.compare(key, t.key);
                if (cmp < 0)
                    t = t.left;
                else if (cmp > 0)
                    t = t.right;
                else
                    return t.setValue(value);
            } while (t != null);
        }
        else {
            if (key == null)
                throw new NullPointerException();
            Comparable<? super K> k = (Comparable<? super K>) key;
            do {
                parent = t;
                cmp = k.compareTo(t.key);
                if (cmp < 0)
                    t = t.left;
                else if (cmp > 0)
                    t = t.right;
                else
                    return t.setValue(value);
            } while (t != null);
        }
        Entry<K,V> e = new Entry<>(key, value, parent);
        if (cmp < 0)
            parent.left = e;
        else
            parent.right = e;
        fixAfterInsertion(e);
        size++;
        modCount++;
        return null;
    }

如何在不调用main方法的情况下调用compare（）方法？

2 个答案: