Java で List コレクションを初期化する 8 つの方法を説明した記事 (コード付き)

List list = new ArrayList<>();
list.add("1");
list.add("2");
list.add("3");
System.out.println("getList1: " + list);

getList1: [1, 2, 3]

// 生成的list不可变
List list = Arrays.asList("1", "2", "3");
System.out.println("getList2: " + list);
// 如果要可变需要用ArrayList包装一下
List numbers = new ArrayList<>(Arrays.asList("1", "2", "3"));
numbers.add("4");
System.out.println("numbers: " + numbers);

getList2: [1, 2, 3]
numbers: [1, 2, 3, 4]

// 生成的list不可变
List list = Collections.nCopies(3, "1");
System.out.println("getList3: " + list);
// 如果要可变需要用ArrayList包装一下
List dogs = new ArrayList<>(Collections.nCopies(3, "dog"));
dogs.add("dog");
System.out.println("dogs: " + dogs);

getList3: [1, 1, 1]
dogs: [dog, dog, dog, dog]

List list = Lists.newArrayList("1", "2", "3");
System.out.println("getList4: " + list);

getList4: [1, 2, 3]

List list = new ArrayList() {{
     add("1");
     add("2");
     add("3");
}};
System.out.println("getList5: " + list);

getList5: [1, 2, 3]

List list = ImmutableList.of("1", "2", "3");
System.out.println("getList6: " + list);

getList6: [1, 2, 3]

List list = Stream.of("1", "2", "3").collect(Collectors.toList());
System.out.println("getList7: " + list);

getList7: [1, 2, 3]

List list = List.of{"1", "2", "3"};
System.out.println("getList8: " + list);

getList8: [1, 2, 3]