java—List，Set，数组的互相转换

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1. 数组与 List
1. List -> 数组
public static void main(String[] args) {
List<String> list = new ArrayList<>();
for (int i = 0; i < 5; i++) {
list.add(“i=” + i);
}

//1. 通过 toArray 方法
String[] array = list.toArray(new String[0]);

//2. stream
String[] array2 = list.stream().toArray(String[]::new);

System.out.println(Arrays.toString(array));
System.out.println(Arrays.toString(array2));
}
2. 数组 -> List
public static void main(String[] args) {
String[] str =new String[] {“aaa”,”bbb”,”ccc”,”ddd”};
List<String> list2 = new ArrayList<>();
//1. Arrays.asList()
List<String> list = Arrays.asList(str);

//2. Collections.addAll(list, arrays)
Collections.addAll(list2, str);

//3. stream
List<String> list3 = Stream.of(str).collect(Collectors.toList());

System.out.println(list.toString());
System.out.println(list2.toString());
System.out.println(list3.toString());
}
2. 数组与 Set
1. 数组 -> Set
public static void main(String[] args) {
String[] str =new String[] {“aaa”,”bbb”,”ccc”,”ddd”};

//1. 通过先转 List 之后引入 Set
Set<String> set = new HashSet<>(Arrays.asList(str));

//2. stream
Set<String> set2 = Stream.of(str).collect(Collectors.toSet());

System.out.println(set);
System.out.println(set2);
}
2. Set -> 数组
public static void main(String[] args) {
Set<String> set = new HashSet<>();
set.add(“aaa”);
set.add(“bbb”);
set.add(“ccc”);
set.add(“ddd”);

//1. 通过 toArray()
String[] array = set.toArray(new String[0]);
//2. stream
String[] array2 = set.stream().toArray(String[]::new);

System.out.println(Arrays.toString(array));
System.out.println(Arrays.toString(array2));
}
3. List 与 Set
1. List -> Set
public static void main(String[] args) {
List<String> list = new ArrayList<>();
list.add(“aaa”);
list.add(“bbb”);
list.add(“ccc”);
list.add(“ddd”);

Set<String> set = new HashSet<>(list);

Set<String> set2 = list.stream().collect(Collectors.toSet());

System.out.println(set.toString());
System.out.println(set2.toString());
}
2. Set -> List
public static void main(String[] args) {
Set<String> set = new HashSet<>();
set.add(“aaa”);
set.add(“bbb”);
set.add(“ccc”);
set.add(“ddd”);

//1. list 构造方法
List<String> list = new ArrayList<>(set);

//2. stream
List<String> list2 = set.stream().collect(Collectors.toList());

System.out.println(list.toString());
System.out.println(list2.toString());
}