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 map = new HashMap<>();
map.put("ad", "dd");
map.put("bc", "ee");
map.put("cb", "ff");
for (Map.Entry entry : map.entrySet()) {
System.out.println(entry.getKey() + ":" + entry.getValue());
}
System.out.println();
Map 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 entry : linkedHashMap.entrySet()) {
System.out.println(entry.getKey() + ":" + entry.getValue());
}
System.out.println();
Map linkedHashMap1 = new LinkedHashMap<>();
// 自定义排序（降序）
map.entrySet().stream().sorted(Map.Entry.comparingByKey(new Comparator() {
@Override
public int compare(String o1, String o2) {
return o2.compareTo(o1);
}
})).forEach(o -> linkedHashMap1.put(o.getKey(), o.getValue()));
for (Map.Entry 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 map = new HashMap<>();
map.put("ad", "dd");
map.put("bc", "ee");
map.put("cb", "ff");
for (Map.Entry entry : map.entrySet()) {
System.out.println(entry.getKey() + ":" + entry.getValue());
}
System.out.println();
// 默认按照升序排序
Map map1 = new TreeMap<>();
map.forEach(map1::put);
for (Map.Entry entry : map1.entrySet()) {
System.out.println(entry.getKey() + ":" + entry.getValue());
}
System.out.println();
// 自定义排序（降序）
Map map2 = new TreeMap<>(new Comparator() {
@Override
public int compare(String o1, String o2) {
return o2.compareTo(o1);
}
});
map.forEach(map2::put);
for (Map.Entry 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 map = new HashMap<>();
map.put("ad", "dd");
map.put("bc", "ee");
map.put("cb", "ff");
for (Map.Entry entry : map.entrySet()) {
System.out.println(entry.getKey() + ":" + entry.getValue());
}
System.out.println();
Map 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 entry : linkedHashMap.entrySet()) {
System.out.println(entry.getKey() + ":" + entry.getValue());
}
System.out.println();
Map linkedHashMap1 = new LinkedHashMap<>();
// 自定义排序（降序）
map.entrySet().stream().sorted(Map.Entry.comparingByValue(new Comparator() {
@Override
public int compare(String o1, String o2) {
return o2.compareTo(o1);
}
})).forEach(o -> linkedHashMap1.put(o.getKey(), o.getValue()));
for (Map.Entry 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
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 map = new HashMap<>();
map.put("ad", "dd");
map.put("bc", "ee");
map.put("cb", "ff");
for (Map.Entry entry : map.entrySet()) {
System.out.println(entry.getKey() + ":" + entry.getValue());
}
System.out.println();
Map sortedMap = new LinkedHashMap<>();
List> entryList = new ArrayList>(
map.entrySet());
Collections.sort(entryList, new Comparator>() {
@Override
public int compare(Map.Entry me1, Map.Entry me2) {
return me1.getValue().compareTo(me2.getValue());
}
});
for (Map.Entry stringStringEntry : entryList) {
sortedMap.put(stringStringEntry.getKey(), stringStringEntry.getValue());
}
for (Map.Entry 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 hashMap = new HashMap();
hashMap.put("name1", "josan1");
hashMap.put("name2", "josan2");
hashMap.put("name3", "josan3");
Set> set = hashMap.entrySet();
Iterator> 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 hashMap = new LinkedHashMap();
hashMap.put("name1", "josan1");
hashMap.put("name2", "josan2");
hashMap.put("name3", "josan3");
Set> set = hashMap.entrySet();
Iterator> 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
以上就是Java实现HashMap排序方法的示例详解的详细内容，更多关于Java HashMap排序的资料请关注脚本之家其它相关文章！