java - TreeMap 是如何排序的

Question

TreeMap 如何排序？例如，您有以下 map :

TreeMap<String, Integer> treemap = new TreeMap<>();
treemap.put("lol", 1);
treemap.put("Marc", 2);
treemap.put("Jesper", 3);

Iterator ittwo = treemap.entrySet().iterator();
    while (ittwo.hasNext()) {
    Map.Entry pairs = (Map.Entry)ittwo.next();
    System.out.println(pairs.getKey() + " = " + pairs.getValue());
    ittwo.remove();
}

这个的输出是:

Jesper = 3
Marc = 2
lol = 1

如果它不是按字母顺序排列的，那么它是什么？

Answer 1

它不仅按字母顺序排列，而且还区分大小写。

TreeMap<String, Integer> treemap = new TreeMap<String, Integer>();
treemap.put("Lol", 1);
treemap.put("Marc", 2);
treemap.put("Jesper", 3);
treemap.put("lol1", 1);
treemap.put("marc1", 2);
treemap.put("jesper1", 3);

输出:

Jesper = 3
Lol = 1
Marc = 2
jesper1 = 3
lol1 = 1
marc1 = 2

因此，如果您不需要它，您可以使用自定义比较器，并比较小写的字符串:

TreeMap<String, Integer> treemap = new TreeMap<String, Integer>(new Comparator<String>() {
    public int compare(String o1, String o2) {
        return o1.toLowerCase().compareTo(o2.toLowerCase());
    }
});
treemap.put("Lol", 1);
treemap.put("Marc", 2);
treemap.put("Jesper", 3);
treemap.put("lol1", 1);
treemap.put("marc1", 2);
treemap.put("jesper1", 3);

输出:

Jesper = 3
jesper1 = 3
Lol = 1
lol1 = 1
Marc = 2
marc1 = 2