温故而知新（一）TreeMap

最新推荐文章于 2022-01-24 20:41:27 发布

原创最新推荐文章于 2022-01-24 20:41:27 发布 · 410 阅读

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本文深入探讨了Java中TreeMap的使用方法，特别是如何通过自定义Comparator实现不同排序方式，包括正序、倒序等，并提供了丰富的示例代码。

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TreeMap一种”有序”的Map

import java.util.Map;
import java.util.TreeMap;
import java.util.Iterator;
import java.util.Map.Entry;
import java.util.Comparator;

public class SortMap {
    public static void main(String[] args) {
        TreeMap<String, Integer> map = new TreeMap<String, Integer>();
        for (String s : args) {
            map.put(s, 1);
        }
        System.out.println("------------------------------default----------------------------");
        print(map);
        System.out.println("------------------------------o2 compareTo o1----------------------------");
        map = new TreeMap<String, Integer>(new Comparator<String>() {

            @Override
            public int compare(String o1, String o2) {
                return o2.compareTo(o1);
            }

        });
        for (String s : args) {
            map.put(s, 1);
        }
        print(map);
        System.out.println("------------------------------0----------------------------");
        map = new TreeMap<String, Integer>(new Comparator<String>() {

            @Override
            public int compare(String o1, String o2) {
                return 0;
            }

        });
        for (String s : args) {
            map.put(s, 1);
        }
        print(map);
        System.out.println("------------------------------1----------------------------");
        map = new TreeMap<String, Integer>(new Comparator<String>() {

            @Override
            public int compare(String o1, String o2) {
                return 1;
            }

        });
        for (String s : args) {
            map.put(s, 1);
        }
        print(map);
        System.out.println("------------------------------2----------------------------");
        map = new TreeMap<String, Integer>(new Comparator<String>() {

            @Override
            public int compare(String o1, String o2) {
                return 2;
            }

        });
        for (String s : args) {
            map.put(s, 1);
        }
        print(map);

        System.out.println("------------------------------- -1----------------------------");
        map = new TreeMap<String, Integer>(new Comparator<String>() {

            @Override
            public int compare(String o1, String o2) {
                return -1;
            }

        });
        for (String s : args) {
            map.put(s, 1);
        }
        print(map);
        System.out.println("------------------------------ -2----------------------------");
        map = new TreeMap<String, Integer>(new Comparator<String>() {

            @Override
            public int compare(String o1, String o2) {
                return -2;
            }

        });
        for (String s : args) {
            map.put(s, 1);
        }
        print(map);
    }


    public static void print(Map<String, Integer> map) {
        Iterator<Entry<String, Integer>> it = map.entrySet().iterator();
        while (it.hasNext()) {
            Entry<String, Integer> entry = it.next();
            System.out.println(entry.getKey() + " --- ");
        }
    }
}