如何在 Java 8 中按键和值对 HashMap 进行排序 - 完整教程

已发表: 2020-09-18

在 Java 8 中——如何对地图进行排序？

在 Crunchify 上，我们编写了近 400 篇 Java 教程，而这一篇是 Java8 类别的补充。

我喜欢 Java 集合，并且有多个关于如何迭代 Map 和 List、LinkedList、JSONArray 等的教程。

在本教程中，我们将介绍 Java8 中按键和值对 HashMap 进行排序的最佳方法。

让我们开始吧：

我们将创建 CrunchifySortMapByKeyValueJava8.java 类
创建 HashMap<String, Integer> crunchifyMap，这就是我们将用于按 Key 和 Value 排序的内容。
For KEY ：我们将从列表中添加随机公司
- 模式：1 到 10 之间的随机数 + (-) + 列表中的 1 家公司
- 公司名单：crunchify.com、google.com、twitter.com
For VALUE ：我们将添加一个介于 1 到 50 之间的随机数
我们将打印原始 Map，按 Key Map 排序，按 Value Map 排序

地图.入口。 comparingByKey()返回一个比较器，它按键的自然顺序比较 Map.Entry。

地图.入口。 comparingByValue()返回一个比较器，它按自然顺序比较 Map.Entry 的值。

这是一个完整的Java代码：

请仔细查看下面代码中提到的两个问题这些是简单的实用程序，以防万一您想在项目中使用它。

如何从 ArrayList 中获取随机值？
如何在 Java 8 中遍历 HashMap？

CrunchifySortMapByKeyValueJava8.java

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package crunchify . com . tutorial ;

import java . util . ArrayList ;

import java . util . HashMap ;

import java . util . LinkedHashMap ;

import java . util . Map ;

import java . util . Random ;

import java . util . stream . Stream ;

/**

* @author Crunchify.com

* Best way to sort HashMap by Key and Value in Java8 - Tutorial by App Shah

public class CrunchifySortMapByKeyValueJava8 {

private static final Random crunchifyRandom = new Random ( ) ;

public static void main ( String [ ] argv ) {

Map < String , Integer > crunchifyMap = new HashMap < > ( ) ;

// Let's first create companies ArrayList

ArrayList <String> companies = new ArrayList < > ( ) ;

companies . add ( "Crunchify.com" ) ;

companies . add ( "Google.com" ) ;

companies . add ( "Twitter.com" ) ;

// Let's add 10 entries to HashMap crunchifyMap

for ( int i = 1 ; i < = 10 ; ++ i ) {

// How to get Random value from ArrayList?

String company = companies . get ( crunchifyRandom . nextInt ( companies . size ( ) ) ) ;

// Basically we are creating

// Key with pattern: 1-Crunchify, 5-Google, and so on...

// Random Value: Number between 1 to 50

crunchifyMap . put ( crunchifyRandom . nextInt ( 10 ) + "-" + company , crunchifyRandom . nextInt ( 50 ) ) ;

}

crunchifyLog ( "~~~~~~~~~~~~~~Original HashMap (crunchifyMap value)~~~~~~~~~~~~~~" ) ;

crunchifyLog ( crunchifyMap ) ;

crunchifyLog ( "\n~~~~~~~~~~~~~~Updated HashMap after Sorting by Key~~~~~~~~~~~~~~" ) ;

// Map: An object that maps keys to values. A map cannot contain duplicate keys; each key can map to at most one value.

Map < String , Integer > key = crunchifySortByKey ( crunchifyMap ) ;

iterateThroughHashMapJava8 ( key ) ;

crunchifyLog ( "\n~~~~~~~~~~~~~~Updated HashMap after Sorting by Value~~~~~~~~~~~~~~" ) ;

Map < String , Integer > value = crunchifySortByValue ( crunchifyMap ) ;

iterateThroughHashMapJava8 ( value ) ;

}

// Simple Log Statement

private static void crunchifyLog ( Object string ) {

System . out . println ( string ) ;

}

// How to Iterate through HashMap in Java 8?

private static void iterateThroughHashMapJava8 ( Map < String , Integer > crunchifyMap ) {

crunchifyMap . forEach ( ( k , v ) - > {

System . out . println ( "Key: " + k + "\t\t\t Value: " + v ) ;

} ) ;

}

// Let's sort HashMap by Key

// Comparable: This interface imposes a total ordering on the objects of each class that implements it.

// This ordering is referred to as the class's natural ordering, and the class's compareTo method is referred to as its natural comparison method.

public static < K extends Comparable < ? super K > , V > Map < K , V > crunchifySortByKey ( Map < K , V > crunchifyMap ) {

Map < K , V > crunchifyResult = new LinkedHashMap < > ( ) ;

Stream < Map . Entry < K , V > > sequentialStream = crunchifyMap . entrySet ( ) . stream ( ) ;

// comparingByKey() returns a comparator that compares Map.Entry in natural order on key.

sequentialStream . sorted ( Map . Entry . comparingByKey ( ) ) . forEachOrdered ( c - > crunchifyResult . put ( c . getKey ( ) , c . getValue ( ) ) ) ;

return crunchifyResult ;

}

// Let's sort HashMap by Value

public static < K , V extends Comparable < ? super V > > Map < K , V > crunchifySortByValue ( Map < K , V > crunchifyMap ) {

Map < K , V > crunchifyResult = new LinkedHashMap < > ( ) ;

// Stream: A sequence of elements supporting sequential and parallel aggregate operations.

// The following example illustrates an aggregate operation using Stream and IntStream.

Stream < Map . Entry < K , V > > sequentialStream = crunchifyMap . entrySet ( ) . stream ( ) ;

// comparingByValue() returns a comparator that compares Map.Entry in natural order on value.

// sorted(): Returns a stream consisting of the elements of this stream, sorted according to the provided Comparator.

sequentialStream . sorted ( Map . Entry . comparingByValue ( ) ) . forEachOrdered ( c - > crunchifyResult . put ( c . getKey ( ) , c . getValue ( ) ) ) ;

// getValue(): Returns the value corresponding to this entry. If the mapping has been removed from the backing map (by the iterator's remove operation), the results of this call are undefined.

// getKey(): Returns the key corresponding to this entry.

return crunchifyResult ;

}

Eclipse 控制台输出：

只需将上面的程序作为 Java 应用程序运行，您应该会看到如下所示的结果。

~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Original HashMap ( crunchifyMap value ) ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

{ 9 - Google . com = 36 , 6 - Twitter . com = 17 , 3 - Google . com = 39 , 2 - Twitter . com = 43 , 5 - Crunchify . com = 2 , 8 - Google . com = 5 , 8 - Crunchify . com = 47 , 5 - Google . com = 10 , 7 - Google . com = 3 }

~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Updated HashMap after Sorting by Key ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Key : 2 - Twitter . com Value : 43

Key : 3 - Google . com Value : 39

Key : 5 - Crunchify . com Value : 2

Key : 5 - Google . com Value : 10

Key : 6 - Twitter . com Value : 17

Key : 7 - Google . com Value : 3

Key : 8 - Crunchify . com Value : 47

Key : 8 - Google . com Value : 5

Key : 9 - Google . com Value : 36

~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Updated HashMap after Sorting by Value ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~