Java之HashMap系列--排序的方法

妖狐艹你老母 2023-09-29 15:24 10阅读 0赞

原文网址：[Java之HashMap系列--排序的方法\_IT利刃出鞘的博客-CSDN博客][Java_HashMap_--_IT_-CSDN]

## 简介 ##

本文用示例介绍HashMap排序的方法。

## 排序已有数据 ##

### 按key排序 ###

**使用stream进行排序（按key升序/降序）**

package org.example.a;
    
    import java.util.*;
    
    public class Demo {
        public static void main(String[] args) {
            Map<String, String> map = new HashMap<>();
            map.put("ad", "dd");
            map.put("bc", "ee");
            map.put("cb", "ff");
            for (Map.Entry<String, String> entry : map.entrySet()) {
                System.out.println(entry.getKey() + ":" + entry.getValue());
            }
            System.out.println();
    
            Map<String, String> linkedHashMap = new LinkedHashMap<>();
            // 默认按照升序排列
            map.entrySet().stream().sorted(Map.Entry.comparingByKey())
                    .forEach(o -> linkedHashMap.put(o.getKey(), o.getValue()));
            for (Map.Entry<String, String> entry : linkedHashMap.entrySet()) {
                System.out.println(entry.getKey() + ":" + entry.getValue());
            }
            System.out.println();
    
            Map<String, String> linkedHashMap1 = new LinkedHashMap<>();
            // 自定义排序（降序）
            map.entrySet().stream().sorted(Map.Entry.comparingByKey(new Comparator<String>() {
                @Override
                public int compare(String o1, String o2) {
                    return o2.compareTo(o1);
                }
            })).forEach(o -> linkedHashMap1.put(o.getKey(), o.getValue()));
            for (Map.Entry<String, String> entry : linkedHashMap1.entrySet()) {
                System.out.println(entry.getKey() + ":" + entry.getValue());
            }
        }
    }

执行结果

bc:ee
    ad:dd
    cb:ff
    
    ad:dd
    bc:ee
    cb:ff
    
    cb:ff
    bc:ee
    ad:dd

**HashMap转TreeMap自定义排序（按key升序/降序）**

package org.example.a;
    
    import java.util.Comparator;
    import java.util.HashMap;
    import java.util.Map;
    import java.util.TreeMap;
    
    public class Demo {
        public static void main(String[] args) {
            Map<String, String> map = new HashMap<>();
            map.put("ad", "dd");
            map.put("bc", "ee");
            map.put("cb", "ff");
            for (Map.Entry<String, String> entry : map.entrySet()) {
                System.out.println(entry.getKey() + ":" + entry.getValue());
            }
            System.out.println();
            // 默认按照升序排序
            Map<String, String> map1 = new TreeMap<>();
            map.forEach(map1::put);
            for (Map.Entry<String, String> entry : map1.entrySet()) {
                System.out.println(entry.getKey() + ":" + entry.getValue());
            }
            System.out.println();
    
            // 自定义排序（降序）
            Map<String, String> map2 = new TreeMap<>(new Comparator<String>() {
                @Override
                public int compare(String o1, String o2) {
                    return o2.compareTo(o1);
                }
            });
            map.forEach(map2::put);
            for (Map.Entry<String, String> entry : map2.entrySet()) {
                System.out.println(entry.getKey() + ":" + entry.getValue());
            }
        }
    }

执行结果

bc:ee
    ad:dd
    cb:ff
    
    ad:dd
    bc:ee
    cb:ff
    
    cb:ff
    bc:ee
    ad:dd

### 按value排序 ###

**使用stream进行排序（按value升序/降序）**

package org.example.a;
    
    import java.util.*;
    
    public class Demo {
        public static void main(String[] args) {
            Map<String, String> map = new HashMap<>();
            map.put("ad", "dd");
            map.put("bc", "ee");
            map.put("cb", "ff");
            for (Map.Entry<String, String> entry : map.entrySet()) {
                System.out.println(entry.getKey() + ":" + entry.getValue());
            }
            System.out.println();
    
            Map<String, String> linkedHashMap = new LinkedHashMap<>();
            // 默认按照升序排列
            map.entrySet().stream().sorted(Map.Entry.comparingByValue())
                    .forEach(o -> linkedHashMap.put(o.getKey(), o.getValue()));
            for (Map.Entry<String, String> entry : linkedHashMap.entrySet()) {
                System.out.println(entry.getKey() + ":" + entry.getValue());
            }
            System.out.println();
    
            Map<String, String> linkedHashMap1 = new LinkedHashMap<>();
            // 自定义排序（降序）
            map.entrySet().stream().sorted(Map.Entry.comparingByValue(new Comparator<String>() {
                @Override
                public int compare(String o1, String o2) {
                    return o2.compareTo(o1);
                }
            })).forEach(o -> linkedHashMap1.put(o.getKey(), o.getValue()));
            for (Map.Entry<String, String> entry : linkedHashMap1.entrySet()) {
                System.out.println(entry.getKey() + ":" + entry.getValue());
            }
        }
    }

执行结果

bc:ee
    ad:dd
    cb:ff
    
    ad:dd
    bc:ee
    cb:ff
    
    cb:ff
    bc:ee
    ad:dd

**借助List进行排序（按value升序/降序）**

原理：将待排序Map中的所有元素置于一个列表中，接着使用Collections的一个静态方法 sort(List<T> list, Comparator<? super T> c) 来排序列表，同样是用比较器定义比较规则。排序后的列表中的元素再依次装入Map，为了肯定的保证Map中元素与排序后的List中的元素的顺序一致，使用了LinkedHashMap数据类型。

本处只写升序代码，降序只是调换个顺序而已。

package org.example.a;
    
    import java.util.*;
    
    public class Demo {
        public static void main(String[] args) {
            Map<String, String> map = new HashMap<>();
            map.put("ad", "dd");
            map.put("bc", "ee");
            map.put("cb", "ff");
            for (Map.Entry<String, String> entry : map.entrySet()) {
                System.out.println(entry.getKey() + ":" + entry.getValue());
            }
            System.out.println();
    
            Map<String, String> sortedMap = new LinkedHashMap<>();
            List<Map.Entry<String, String>> entryList = new ArrayList<Map.Entry<String, String>>(
                    map.entrySet());
            Collections.sort(entryList, new Comparator<Map.Entry<String, String>>() {
                @Override
                public int compare(Map.Entry<String, String> me1, Map.Entry<String, String> me2) {
                    return me1.getValue().compareTo(me2.getValue());
                }
            });
            for (Map.Entry<String, String> stringStringEntry : entryList) {
                sortedMap.put(stringStringEntry.getKey(), stringStringEntry.getValue());
            }
    
            for (Map.Entry<String, String> entry : sortedMap.entrySet()) {
                System.out.println(entry.getKey() + ":" + entry.getValue());
            }
        }
    }

运行结果

bc:ee
    ad:dd
    cb:ff
    
    ad:dd
    bc:ee
    cb:ff

## **按插入顺序存放** ##

### HashMap不按插入顺序存放 ###

package org.example.a;
    
    import java.util.*;
    
    public class Demo{
        public static List arrayList = new ArrayList();
        public static void main(String[] args) {
            Map<String, String> hashMap = new HashMap<String, String>();
            hashMap.put("name1", "josan1");
            hashMap.put("name2", "josan2");
            hashMap.put("name3", "josan3");
            
            Set<Map.Entry<String, String>> set = hashMap.entrySet();
            Iterator<Map.Entry<String, String>> iterator = set.iterator();
            while(iterator.hasNext()) {
                Map.Entry entry = iterator.next();
                String key = (String) entry.getKey();
                String value = (String) entry.getValue();
                System.out.println("key:" + key + ", value:" + value);
            }
        }
    }

执行结果（未按照插入顺序输出）

key:name3, value:josan3
    key:name2, value:josan2
    key:name1, value:josan1

### LinkedHashMap会按照插入顺序存放 ###

package org.example.a;
    
    import java.util.*;
    
    public class Demo{
        public static List arrayList = new ArrayList();
        public static void main(String[] args) {
            Map<String, String> hashMap = new LinkedHashMap<String, String>();
            hashMap.put("name1", "josan1");
            hashMap.put("name2", "josan2");
            hashMap.put("name3", "josan3");
    
            Set<Map.Entry<String, String>> set = hashMap.entrySet();
            Iterator<Map.Entry<String, String>> iterator = set.iterator();
            while(iterator.hasNext()) {
                Map.Entry entry = iterator.next();
                String key = (String) entry.getKey();
                String value = (String) entry.getValue();
                System.out.println("key:" + key + ", value:" + value);
            }
        }
    }

执行结果（按照插入顺序输出）

key:name1, value:josan1
    key:name2, value:josan2
    key:name3, value:josan3

[Java_HashMap_--_IT_-CSDN]: https://knife.blog.csdn.net/article/details/124903172