如何初始化Map，java

 

 原來路徑：https://www.itranslater.com/qa/details/2104117160695038976

java - 如何初始化靜態Map？

import com.google.common.collect.ImmutableMap;

import java.util.AbstractMap.SimpleEntry;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
import java.util.stream.Collectors;
import java.util.stream.Stream;

/**
 * @Auther: Liruilong
 * @Date: 2020/7/25 13:40
 * @Description:
 */
public class test {

    // 靜態Map的初始化，實際情況中，可以使用枚舉代替
    // 方法一
    public static final Map<Integer, String> myMap_0 = new HashMap<Integer, String>();

    static {
        myMap_0.put(1, "one");
        myMap_0.put(2, "two");
    }
    // 方法二 JDK5
    public static final Map<Integer, String> myMap_1 = new HashMap<Integer, String>() {{
        put(1, "one");
        put(2, "two");
    }};
    // 方法三  Guava
    static final Map<Integer,String> myMap_2 = ImmutableMap.<Integer, String> builder().put(1, "one").put(2, "two").build();

    // 方法四，不超過5個的時候  Guava
    static final Map<Integer, String> myMap_3 = ImmutableMap.of(
        1, "one",
        2, "two"
    );

    // 方法五  Collections.unmodifiableMap()  通過工具類實現


    // 方法六 JDK8
    static final Map<Integer, String> MY_MAP = Arrays.stream(new Object[][]{
        {1, "one"},
        {2, "two"},
    }).collect(Collectors.toMap(kv -> (Integer) kv[0], kv -> (String) kv[1]));


    private static final Map<Integer, String> myMap = Stream.of(
        new SimpleEntry<>(1, "one"),
        new SimpleEntry<>(2, "two"),
        new SimpleEntry<>(3, "three"),
        new SimpleEntry<>(4, "four"),
        new SimpleEntry<>(5, "five"),
        new SimpleEntry<>(6, "six"),
        new SimpleEntry<>(7, "seven"),
        new SimpleEntry<>(8, "eight"),
        new SimpleEntry<>(9, "nine"),
        new SimpleEntry<>(10, "ten"))
        .collect(Collectors.toMap(SimpleEntry::getKey, SimpleEntry::getValue));

}