IO习题

/**
* 一致student_info.txt文件中有一组数据按照格式【姓名-年龄-分数】存储
* 运用IO获取将该文件中的数据分别封装成5个student对象存入到集合中
* 要求根据学生的总分进行排序（降序），如果分数相同则比较年龄（降序）。并且输出展示
*/
private static void demo4() {
List students=new ArrayList<>(10);
try (
BufferedReader reader = new BufferedReader(new FileReader("student_info.txt"))
) {
String s;
while ((s=reader.readLine())!=null){
String[] split = s.split("-");
students.add(new Student(split[0],Integer.parseInt(split[1]),Integer.parseInt(split[2])));
}
List collect = students.stream().sorted(new Comparator() {
@Override
public int compare(Student o1, Student o2) {
return o2.getScore() - o1.getScore();
}
}.thenComparing(Student::getAge).reversed()).collect(Collectors.toList());
collect.forEach(System.out::println);
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}

/**
 * 使用集合相关功能，存储10个数据（1~50的随机偶数），要求数字不能重复，添加完成后从大到小倒序遍历输出到控制台
 * 并且使用io流将集合中的元素按照指定格式输出到置顶文件中
 */
private static void demo3() {
    ThreadLocalRandom random = ThreadLocalRandom.current();
    Set<Integer> set = new HashSet<>(10);
    while (set.size() < 20) {
        int i = random.nextInt(1, 51);
        if (i % 2 == 0)
            set.add(i);
    }
    List<Integer> collect = set.stream().collect(Collectors.toList());
    Collections.sort(collect, ((Integer o1, Integer o2) -> o2 - o1));
    try (
            OutputStream stream = new FileOutputStream("e.txt")
    ) {
        String string = collect.toString();
        stream.write(string.getBytes());
        //[46, 44, 42, 40, 38, 36, 34, 32, 28, 24, 22, 20, 18, 16, 14, 12, 10, 8, 6, 4]
    } catch (FileNotFoundException e) {

    } catch (IOException e) {
        e.printStackTrace();
    }

}

/**
 * 读取任意txt文件内容，并统计出这个文本中每个字符以及每个字符出现的次数，并且以下格式：
 * 字符=次数，持久化保存在文件中
 */
private static void demo2() {
    Map<String, Integer> map = new HashMap<>(16);
    try (
            BufferedReader reader = new BufferedReader(new FileReader("a.txt"));
            BufferedWriter writer = new BufferedWriter(new FileWriter("c.txt"))
    ) {
        int len;
        while ((len = reader.read()) != -1) {
            char a = (char) len;
            String s = String.valueOf(a);
            if (map.get(s) != null) {
                map.put(s, map.get(s) + 1);
            } else {
                map.put(s, 1);
            }
        }
        System.out.println(map);
        Set<Map.Entry<String, Integer>> entries = map.entrySet();
        for (Map.Entry<String, Integer> entry : entries) {
            writer.write(entry.getKey());
            writer.write("=");
            writer.write(String.valueOf(entry.getValue()));
            writer.newLine();
        }
    } catch (FileNotFoundException e) {
    } catch (IOException e) {
        e.printStackTrace();
    }
}

/**
 * 已知文件a.txt中的内容为：AAbcdea22dfewplkCC321ou1,
 * 请编写程序读取该文件内容，要求去掉重复字母，并且按照自然顺序后输出到b.txt
 */
private static void demo1() {
    try (
            BufferedReader reader = new BufferedReader(new FileReader("a.txt"));
            BufferedWriter writer = new BufferedWriter(new FileWriter("b.txt"))
    ) {
        String s = reader.readLine();
        char[] chars = s.toCharArray();
        Arrays.sort(chars);
        s = new String(chars);
        s = s.replaceAll("(.)\\1+", "$1");
        writer.write(s);
    } catch (IOException e) {
        e.printStackTrace();
    }
}