Java 8 将Map转换为List

将一个Java示例转换Map为List

Map<String, String> map = new HashMap<>();

// Convert all Map keys to a List
List<String> result = new ArrayList(map.keySet());

// Convert all Map values to a List
List<String> result2 = new ArrayList(map.values());

// Java 8, Convert all Map keys to a List
List<String> result3 = map.keySet().stream()
	.collect(Collectors.toList());

// Java 8, Convert all Map values  to a List
List<String> 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<String> 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

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<Integer, String> 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("\n1. Export Map Key to List...");

        List<Integer> result = new ArrayList(map.keySet());

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

        System.out.println("\n2. Export Map Value to List...");

        List<String> 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

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<Integer, String> 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("\n1. Export Map Key to List...");

        List<Integer> result = map.keySet().stream()
                .collect(Collectors.toList());

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

        System.out.println("\n2. Export Map Value to List...");

        List<String> result2 = map.values().stream()
                .collect(Collectors.toList());

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

        System.out.println("\n3. Export Map Value to List..., say no to banana");
        List<String> 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

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<Integer, String> 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<Integer> resultSortedKey = new ArrayList<>();
        List<String> resultValues = map.entrySet().stream()
                //sort a Map by key and stored in resultSortedKey
                .sorted(Map.Entry., String>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