java集合类的相关转换

下面的的案例，基本上是以代码为主，文字的描述较少，后期有时间会继续添加。

ArrayToList

public void ArrayToList() {
    System.out.println("ArrayToList");
    Object[] objects = new Object[]{"纽约", "伦敦", "法兰克福", "东京", "多伦多"};
    //方法一
    List<Object> list = new ArrayList<>(Arrays.asList(objects));
    System.out.println(list);
    //方法二
    System.out.println("使用java8特性的方法");
    List<Object> list1 = Stream.of(objects).collect(Collectors.toList());
    System.out.println(list1);
}

ArrayToMap

public void ArrayToMap() {
    System.out.println("ArrayToMap");
    Object[] objects = new Object[]{"纽约", "伦敦", "法兰克福", "东京", "多伦多"};
    Map<Object, Object> map = new HashMap<>();
    int i = 1;
    for (Object o : objects) {
        map.put(i++, o);
    }
    System.out.println(map);
}

ArrayToSet

public void ArrayToSet() {
    System.out.println("ArrayToMap");
    Object[] objects = new Object[]{"纽约", "伦敦", "法兰克福", "东京", "多伦多"};
    //方法一
    Set<Object> set = new HashSet<>(Arrays.asList(objects));
    System.out.println(set);
    //方法二
    System.out.println("使用java8特性的方法");
    Set<Object> set1 = Stream.of(objects).collect(Collectors.toSet());
}

ListToArray

public void ListToArray() {
    System.out.println("ListToArray");
    List<String> list = new ArrayList<>();
    list.add("布朗克斯");
    list.add("布鲁克林");
    list.add("曼哈顿");
    list.add("皇后区");
    list.add("斯塔滕岛");
    //方法一
    String[] strings = list.toArray(new String[list.size()]);
    System.out.println(Arrays.toString(strings));
    //方法二
    System.out.println("使用java8特性的方法");
    String[] strings1 = list.stream().toArray(String[]::new);
    System.out.println(Arrays.toString(strings1));
}

ListToMap

新建一个Book类（model）

class Book {
    private String name;
    private Integer releaseYear;
    private String isbn;

    @Override
    public String toString() {
        return "Book{" +
                "name='" + name + '\'' +
                ", releaseYear=" + releaseYear +
                ", isbn='" + isbn + '\'' +
                '}';
    }

    public Book(String name, int releaseYear, String isbn) {
        this.name = name;
        this.releaseYear = releaseYear;
        this.isbn = isbn;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getReleaseYear() {
        return releaseYear;
    }

    public void setReleaseYear(int releaseYear) {
        this.releaseYear = releaseYear;
    }

    public String getIsbn() {
        return isbn;
    }

    public void setIsbn(String isbn) {
        this.isbn = isbn;
    }
}

主要方法

public void ListToMap() {
    System.out.println("ListToMap");
    Map<Object, Object> map = new HashMap<>();
    List<String> list = new ArrayList<>();
    list.add("布朗克斯");
    list.add("布鲁克林");
    list.add("曼哈顿");
    list.add("皇后区");
    list.add("斯塔滕岛");
    //方法一
    for (int i = 0; i < list.size(); i++) {
        map.put("第" + i + 1 + "区", list.get(i));
    }
    System.out.println(map);
    //方法二
    List<Book> bookList = new ArrayList<>();
    bookList.add(new Book("平凡的世界", 2004, "9787020048045"));
    bookList.add(new Book("战争与和平", 1989, "9787020014071"));
    bookList.add(new Book("百年孤独", 1775, "9787215069657"));
    for (int i = 0; i < bookList.size(); i++) {
        System.out.println(bookList.get(i).toString());
    }
    Map<String, Integer> map1 = bookList.stream().collect(Collectors.toMap(Book::getName, Book::getReleaseYear));
    System.out.println(map1);

}

ListToSet

public void ListToSet() {
    System.out.println("ListToSet");
    Set<Object> set = new HashSet<>();
    List<String> list = new ArrayList<>();
    list.add("布朗克斯");
    list.add("布鲁克林");
    list.add("曼哈顿");
    list.add("皇后区");
    list.add("斯塔滕岛");
    for (Object i : list) {
        set.add(i);
    }
    System.out.println(set);
}

MapToArray

public void MapToArray() {
    System.out.println("MapToArray");
    Map<String, String> map = new HashMap<>();
    map.put("甘肃", "兰州");
    map.put("陕西", "西安");
    map.put("新疆", "乌鲁木齐");
    map.put("青海", "西宁");
    map.put("宁夏", "银川");
    Object[][] strings = new Object[map.size()][2];
    Iterator iterator = map.entrySet().iterator();
    for (int i = 0; i < map.size(); i++) {
        Map.Entry entry = (Map.Entry) iterator.next();
        strings[i][0] = entry.getKey();
        strings[i][1] = entry.getValue();
    }
    for (Object[] objects : strings) {
        for (Object objects1 : objects) {
            System.out.print(objects1 + " ");
        }
        System.out.println();
    }
}

MapToList

public void MapToList() {
    System.out.println("MapToList");
    Map<String, String> map = new HashMap<>();
    map.put("甘肃", "兰州");
    map.put("陕西", "西安");
    map.put("新疆", "乌鲁木齐");
    map.put("青海", "西宁");
    map.put("宁夏", "银川");
    List<Object> objects = new ArrayList<>(map.keySet());
    System.out.println(objects);
    //list里面放置list
    List<List<Object>> lists = new ArrayList<>();
    for (Object o : map.keySet()) {
        List<Object> objects1 = new ArrayList<>();
        objects1.add(o);
        objects1.add(map.get(o));
        lists.add(objects1);
    }
    System.out.println(lists);
}

MapToSet

public void MapToSet() {
    System.out.println("MapToSet");
    Map<String, String> map = new HashMap<>();
    map.put("甘肃", "兰州");
    map.put("陕西", "西安");
    map.put("新疆", "乌鲁木齐");
    map.put("青海", "西宁");
    map.put("宁夏", "银川");
    Set<Object> objects = new HashSet<>(map.keySet());
    System.out.println(objects);
}

SetToArray

public void SetToArray() {
    System.out.println("SetToArray");
    Set<Object> set = new HashSet<>();
    set.add("北京");
    set.add("上海");
    set.add("深圳");
    set.add("广州");
    Object[] objects = set.toArray(new Object[set.size()]);
    System.out.println(Arrays.toString(objects));
}

SetToList

public void SetToList() {
    System.out.println("SetToList");
    Set<Object> set = new HashSet<>();
    set.add("北京");
    set.add("上海");
    set.add("深圳");
    set.add("广州");
    List<Object> list = new ArrayList<>(set);
    System.out.println(list);
}

SetToMap

public void SetToMap() {
    System.out.println("SetToMap");
    Set<Object> set = new HashSet<>();
    set.add("北京");
    set.add("上海");
    set.add("深圳");
    set.add("广州");
    Map<Object, Object> map = new HashMap<>();
    Iterator iterator = set.iterator();
    for (int i = 0; i < set.size(); i++) {
        map.put(i, iterator.next());
    }
    System.out.println(map);
}