Java面试知识点：红黑树、Stream流

喜欢ヅ旅行 2022-09-07 12:21 148阅读 0赞

# 问题：Java面试知识点：红黑树、Stream流 #

答案：

1.红黑树

红黑树  
• 平衡二叉B树  
• 每一个节点可以是红或者黑  
• 红黑树不是高度平衡的，它的平衡是通过“自己的红黑规则”进行实现的

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmcxMzU2Mzc1ODEyOA_size_16_color_FFFFFF_t_70][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmcxMzU2Mzc1ODEyOA_size_16_color_FFFFFF_t_70 1][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmcxMzU2Mzc1ODEyOA_size_16_color_FFFFFF_t_70 2][]

2.Stream流

Stream流的常见中间操作方法  
• Stream<T> limit(long maxSize) : 截取指定参数个数的数据  
• Stream<T> skip(long n):跳过指定参数个数的数据  
• static <T> Stream<T> concat(Stream a, Stream b):合并a和b两个流为一个流  
• Stream<T> distinct() :去除流中重复的元素。依赖(hashCode和equals方法)

在流中无法直接修改数据源中的数据。

代码如下：

public class test15Stream {
        public static void main(String[] args) {
            ArrayList<String> list=new ArrayList<>();
            list.add("杨大大");
            list.add("恒大大");
    
    //        Stream<String> stream=list.stream();
    //        stream.forEach(s-> System.out.println(s));
            list.stream().forEach(s-> System.out.println(s));
            HashMap<String,Integer> map=new HashMap<>();
            map.put("杨大大",22);
            map.put("恒大大",22);
            Set<String> keySet = map.keySet();
            keySet.stream().forEach(s-> System.out.println(s));
            Set<Map.Entry<String, Integer>> entries = map.entrySet();
            entries.stream().forEach(s-> System.out.println(s));
    
            int[] arr={1,2};
            Arrays.stream(arr).forEach(s-> System.out.println(s));
            Stream.of(1,2).forEach(s-> System.out.println(s));
            list.stream().filter(new Predicate<String>() {
                @Override
                public boolean test(String s) {
                    boolean b = s.startsWith("杨");
                    return b;
                }
            }).forEach(s-> System.out.println(s));
            list.stream().filter(s->{
                boolean b = s.startsWith("杨");
                return b;
            }).forEach(s-> System.out.println(s));
            list.stream().filter(s->s.startsWith("杨")
            ).forEach(s-> System.out.println(s));
            list.stream().limit(2).forEach(s-> System.out.println(s));
            list.stream().skip(1).forEach(s-> System.out.println(s));
        }
    }

public class test16Stream {
        public static void main(String[] args) {
            ArrayList<String> list=new ArrayList<>();
            list.add("杨大大");
            list.add("恒大大");
    
    
            Stream.of(1,2).forEach(s-> System.out.println(s));
            list.stream().filter(new Predicate<String>() {
                @Override
                public boolean test(String s) {
                    boolean b = s.startsWith("杨");
                    return b;
                }
            }).forEach(s-> System.out.println(s));
            list.stream().filter(s->{
                boolean b = s.startsWith("杨");
                return b;
            }).forEach(s-> System.out.println(s));
            list.stream().filter(s->s.startsWith("杨")
            ).forEach(s-> System.out.println(s));
            list.stream().limit(2).forEach(s-> System.out.println(s));
            list.stream().skip(1).forEach(s-> System.out.println(s));
            ArrayList<String> list1=new ArrayList<>();
            list1.add("杨大大");
            list1.add("恒大大");
            Stream.concat(list.stream(),list1.stream()).forEach(s-> System.out.println(s));
            list1.add("恒大大");
            //forEach方法的底层，会循环获取到流中的每一个数据，
            //并循环调用accept方法，并把每一个数据传递给accept方法
            //s就依次表示了流中的每一个数据,
            //所以，我们只要在accept方法中，写上处理的业务逻辑就可以了。
            list1.stream().distinct().forEach(s-> System.out.println(s));
            long count = list1.stream().count();
            System.out.println(count);
        }
    }

public class test17Stream {
        public static void main(String[] args) {
            ArrayList<Integer> list=new ArrayList<>();
            for (int i = 1; i <= 10; i++) {
                list.add(i);
            }
            list.stream().filter(new Predicate<Integer>() {
                @Override
                public boolean test(Integer integer) {
                    return integer%2==0;
                }
            }).forEach(s-> System.out.println(s));
            list.stream().filter(integer -> integer%2==0).forEach(s-> System.out.println(s));
            List<Integer> collect = list.stream().filter(integer -> integer % 2 == 0).
                    collect(Collectors.toList());
            System.out.println(collect);
            Set<Integer> collect1 = list.stream().filter(integer -> integer % 2 == 0).
                    collect(Collectors.toSet());
            System.out.println(collect1);
    
        }
    }

public class Actor {
        private String name;
    
        @Override
        public String toString() {
            return "Actor{" +
                    "name='" + name + '\'' +
                    '}';
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public Actor(String name) {
            this.name = name;
        }
    
        public Actor() {
        }
    }
    
    
    
    public class test18Stream {
        public static void main(String[] args) {
            ArrayList<String> list = new ArrayList<>();
            list.add("杨大大,22");
            list.add("恒大大,23");
            Map<String, Integer> collect = list.stream().filter(s -> {
                String[] split = s.split(",");
                if (Integer.parseInt(split[1]) > 22) {
                    return true;
                }
                ;
                return false;
            }).collect(Collectors.toMap(
                    (String s) -> {
                        return s.split(",")[0];
                    },
                    (String s) -> {
                        return Integer.parseInt(s.split(",")[1]);
                    }
            ));
            System.out.println(collect);
    
            ArrayList<String> actors=new ArrayList<>();
            actors.add("杨洋");
            actors.add("李易峰");
            actors.add("易烊千玺");
            actors.add("胡歌");
            ArrayList<String> actors1=new ArrayList<>();
            actors1.add("杨幂");
            actors1.add("杨紫");
            actors1.add("杨颖");
            actors1.add("迪丽热巴");
    
            Stream<String> stream = actors.stream().filter(s -> s.length() == 3).limit(2);
            Stream<String> stream1 = actors1.stream().filter(s -> s.startsWith("杨")).skip(1);
            Stream.concat(stream,stream1).forEach(name->{
                Actor actor=new Actor(name);
                System.out.println(actor);
            });
        }
    }

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmcxMzU2Mzc1ODEyOA_size_16_color_FFFFFF_t_70]: /images/20220829/4261f426651341069c428185e844b5d1.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmcxMzU2Mzc1ODEyOA_size_16_color_FFFFFF_t_70 1]: /images/20220829/1774205b012e4702934ed3c18e88b791.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmcxMzU2Mzc1ODEyOA_size_16_color_FFFFFF_t_70 2]: /images/20220829/df354c3028534e52b7b7592f5f5dddd0.png