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
请先 ！