Java初始化List集合的7种方式

List<String> list1 = new ArrayList<>();
list1.add("money");
list1.add("study");
list1.add("health");
System.out.println("常规方法：  " + list1); //常规方法：  [money, study, health]

//生成的list不可变
List<String> list2 = Arrays.asList("money", "study", "health");
System.out.println("Arrays工具类：  " + list2); //Arrays工具类：  [money, study, health]
//list2.add("happy");  //报异常 java.lang.UnsupportedOperationException

List<String> list22 = new ArrayList<>(Arrays.asList("abc", "def", "ghi"));
list22.add("xyz");
System.out.println("Arrays工具类、ArrayList包装：  " + list22); //Arrays工具类、ArrayList包装：  [abc, def, ghi, xyz]

//生成的list不可变
List<String> list3 = Collections.nCopies(3, "happy");
System.out.println("Collections工具类：  " + list3); //Collections工具类：  [happy, happy, happy]
//list3.add("happy");  //报异常 java.lang.UnsupportedOperationException

List<String> list33 = new ArrayList<>(Collections.nCopies(3, "up"));
list33.add("down");
System.out.println("Collections工具类、ArrayList包装：  " + list33); //Collections工具类、ArrayList包装：  [up, up, up, down]

//可变
List<String> list4 = new ArrayList<String>() {{
    add("money");
    add("study");
    add("health");
}};
System.out.println("匿名内部类：  " + list4); //匿名内部类：  [money, study, health]

//可变
List<String> list5 = Stream.of("money", "study", "health").collect(Collectors.toList());
System.out.println("JDK8 Stream：  " + list5); //JDK8 Stream：  [money, study, health]

//生成的list不可变
List<String> list6 = List.of("money", "study", "health");
//JDK9 List.of：  [money, study, health]
System.out.println("JDK9 List.of：  " + list6);

//生成的list不可变
List<String> list7 = ImmutableList.of("money", "study", "health");
//ImmutableList:  [money, study, health]
System.out.println("ImmutableList:  " + list7);