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Java 8 将地图转换为列表

最编程 2024-06-29 08:02:31
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将一个Java示例转换Map为List

汇总：

Map map = new HashMap<>();

// Convert all Map keys to a List

List result = new ArrayList(map.keySet());

// Convert all Map values to a List

List result2 = new ArrayList(map.values());

// Java 8, Convert all Map keys to a List

List result3 = map.keySet().stream()

.collect(Collectors.toList());

// Java 8, Convert all Map values to a List

List result4 = map.values().stream()

.collect(Collectors.toList());

// Java 8, seem a bit long, but you can enjoy the Stream features like filter and etc.

List result5 = map.values().stream()

.filter(x -> !“apple”.equalsIgnoreCase(x))

.collect(Collectors.toList());

// Java 8, split a map into 2 List, it works!

// refer example 3 below

~~~~~~~~~~~~~~~~~~~~~~~~~~

分类：

1.映射到List

为了简单Map的List转换，只需使用下面的代码：

ConvertMapToList.java

package com.mkyong;

import java.util.ArrayList;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

public class ConvertMapToList {

public static void main(String[] args) {

Map map = new HashMap<>();

map.put(10, “apple”);

map.put(20, “orange”);

map.put(30, “banana”);

map.put(40, “watermelon”);

map.put(50, “dragonfruit”);

System.out.println(" 1. Export Map Key to List…");

List result = new ArrayList(map.keySet());

result.forEach(System.out::println);

System.out.println(" 2. Export Map Value to List…");

List result2 = new ArrayList(map.values());

result2.forEach(System.out::println);

}

}

Output

1. Export Map Key to List…

50

20

40

10

30

2. Export Map Value to List…

dragonfruit

orange

watermelon

apple

banana

2.Java 8 - 映射到List

对于Java 8，您可以将其Map转换为流，将其处理并将其返回List

ConvertMapToList.java

package com.mkyong;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

import java.util.stream.Collectors;

public class ConvertMapToList {

public static void main(String[] args) {

Map map = new HashMap<>();

map.put(10, “apple”);

map.put(20, “orange”);

map.put(30, “banana”);

map.put(40, “watermelon”);

map.put(50, “dragonfruit”);

System.out.println(" 1. Export Map Key to List…");

List result = map.keySet().stream()

.collect(Collectors.toList());

result.forEach(System.out::println);

System.out.println(" 2. Export Map Value to List…");

List result2 = map.values().stream()

.collect(Collectors.toList());

result2.forEach(System.out::println);

System.out.println(" 3. Export Map Value to List…, say no to banana");

List result3 = map.keySet().stream()

.filter(x -> !“banana”.equalsIgnoreCase(x))

.collect(Collectors.toList());

result3.forEach(System.out::println);

}

}

Output

1. Export Map Key to List…

50

20

40

10

30

2. Export Map Value to List…

dragonfruit

orange

watermelon

apple

banana

3. Export Map Value to List…, say no to banana

dragonfruit

orange

watermelon

apple

3.Java 8 - 将Map转换成List

这个例子有点极端，map.entrySet()用来转换Map成List

ConvertMapToList.java

package com.mkyong;

import java.util.ArrayList;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

import java.util.stream.Collectors;

//https://www.mkyong.com/java8/java-8-how-to-sort-a-map/

public class ConvertMapToList {

public static void main(String[] args) {

Map map = new HashMap<>();

map.put(10, “apple”);

map.put(20, “orange”);

map.put(30, “banana”);

map.put(40, “watermelon”);

map.put(50, “dragonfruit”);

// split a map into 2 List

List resultSortedKey = new ArrayList<>();

List resultValues = map.entrySet().stream()

//sort a Map by key and stored in resultSortedKey

.sorted(Map.Entry.comparingByKey().reversed())

.peek(e -> resultSortedKey.add(e.getKey()))

.map(x -> x.getValue())

// filter banana and return it to resultValues

.filter(x -> !“banana”.equalsIgnoreCase(x))

.collect(Collectors.toList());

resultSortedKey.forEach(System.out::println);

resultValues.forEach(System.out::println);

}

}

Output

//resultSortedKey

50

40

30

20

10

//resultValues

dragonfruit

watermelon

orange

apple

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