Map的集中创建方式整理

Bertha 。 2023-06-13 06:29 14阅读 0赞

package com.zsx.test;
    
    import com.google.common.collect.ArrayListMultimap;
    import com.google.common.collect.ImmutableMap;
    import com.google.common.collect.Maps;
    import com.google.common.collect.Multimap;
    import org.junit.jupiter.api.Test;
    
    import java.util.HashMap;
    import java.util.List;
    import java.util.Map;
    
    /**
     *  测试背景：JDK13、Junit5、IDEA2019.2.3、guava
     */
    public class MapTest {
    
        @Test
        void testCreate1() {
            var map = new HashMap<>();
            map.put("Name", "zhaoyun");
            map.put("age", "20");
            map.put("height", null);
            map.put(null, null);
            System.out.println(map);
        }
    
        @Test
        void testCreate2() {
            var map = new HashMap<>() {
                {
                    put("Name", "zhaoyun");
                    put("age", "20");
                    put("height", null);
                    put(null, null);
                }
    
            };
            System.out.println(map);
        }
    
        /**
         * key和value都不能为空
         */
        @Test
        void testCreate3() {
            // 不可变集合ImmutableCollections
            var map = Map.of("Name", "zhaoyun", "age", "20");
            try {
                // key与value都不能为空 java.lang.NullPointerException
                map = Map.of("Name", "zhaoyun", "age", "20", "height", null);
            } catch (NullPointerException e) {
                e.printStackTrace();
            }
            try {
                map = Map.of("Name", "zhaoyun", "age", "20", null, "null");
            } catch (NullPointerException e) {
                e.printStackTrace();
            }
            // 不能再添加新元素，否则报异常java.lang.UnsupportedOperationException
    //        map.put("height", null);
            System.out.println(map);
            map = Map.of("Name", "zhaoyun", "age", "20");
            System.out.println(map);
        }
    
        @Test
        void testCreate4() {
            var map = Maps.newHashMap();
            map.put("Name", "zhaoyun");
            map.put("age", "20");
            map.put("height", null);
            map.put(null, null);
            System.out.println(map);
        }
    
        /**
         * key和value不能为空
         */
        @Test
        void testCreate5() {
            var map = ImmutableMap. builder()
                .put("Name", "zhaoyun")
                .put("age", "20").build();
            try {
                map = ImmutableMap. builder()
                        .put("Name", "zhaoyun")
                        .put("age", "20")
                        // value不能为空 java.lang.NullPointerException
                        .put("height", null).build();
            } catch (NullPointerException e) {
                e.printStackTrace();
            }
            try {
                map = ImmutableMap. builder()
                        .put("Name", "zhaoyun")
                        .put("age", "20")
                        // key不能为空 java.lang.NullPointerException
                        .put(null, "abc").build();
                System.out.println(map);
            } catch (NullPointerException e) {
                e.printStackTrace();
            }
            System.out.println(map);
        }
    
        @Test
        void testCreate6() {
            Multimap multimap = ArrayListMultimap.create();
            multimap.put("java", "first");
            multimap.put("c#", "second");
            multimap.put("php", "third");
            multimap.put(null, "fourth");
            multimap.put("fifth", null);
            multimap.put("java", Map.of("name", "zsx", "age", 30));
            multimap.put("c#", List.of("name", "age", ""));
            System.out.println(multimap);
        }
    }