@Override public StringBuilder append(CharSequence s, int start, int end) { super.append(s, start, end); return this; }讲一下这个方法

这是Java中StringBuilder类的一个方法，它的作用是将指定字符序列（即字符串）的一部分添加到当前StringBuilder对象中，并返回当前StringBuilder对象的引用。

具体来说，该方法接受三个参数：要添加的字符序列s、开始位置start和结束位置end。它将从s的start位置开始，一直添加到end-1位置（即不包括end位置的字符），并将结果存储在当前StringBuilder对象中。

最后，该方法返回当前StringBuilder对象的引用，以便支持链式调用。这意味着您可以像这样使用该方法：

StringBuilder sb = new StringBuilder();
sb.append("Hello ").append("world!");

在这个例子中，第一次调用append方法将"Hello "添加到StringBuilder对象中，然后返回该对象的引用。然后，第二次调用append方法将"world!"添加到相同的对象中，最终得到的结果是"Hello world!"。

相关问题

@Bean public BCryptPasswordEncoder passwordEncoder() { return new BCryptPasswordEncoder(); }怎样把这段代码改为MD5加密

要将该代码修改为使用MD5加密算法，可以使用Java自带的MessageDigest类，如下所示：

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import org.springframework.context.annotation.Bean;
import org.springframework.security.crypto.password.PasswordEncoder;
import org.springframework.security.crypto.password.StandardPasswordEncoder;

@Bean
public PasswordEncoder passwordEncoder() {
    return new PasswordEncoder() {

        @Override
        public String encode(CharSequence rawPassword) {
            try {
                MessageDigest md = MessageDigest.getInstance("MD5");
                md.update(rawPassword.toString().getBytes());
                byte[] digest = md.digest();
                StringBuilder sb = new StringBuilder();
                for (byte b : digest) {
                    sb.append(String.format("%02x", b & 0xff));
                }
                return sb.toString();
            } catch (NoSuchAlgorithmException e) {
                throw new RuntimeException("Error encoding password", e);
            }
        }

        @Override
        public boolean matches(CharSequence rawPassword, String encodedPassword) {
            return encodedPassword.equals(encode(rawPassword));
        }
    };
}

这个方法创建了一个新的PasswordEncoder实例，该实例使用MD5算法对密码进行加密。encode方法使用MessageDigest类将原始密码转换为MD5哈希值，并返回哈希值的字符串表示形式。matches方法将输入的原始密码转换为哈希值，并将其与存储的哈希值进行比较，以验证密码是否匹配。

请设计一个类型，提供如下方法 提示 要统计每个单词出现的次数，由于一个方法不能返回2种类型，我们需要把单词和它的出现次数封装到一个类中 去，所以，可以定义一个类型如下： 由于我们统计的有多个单词，所以，我们上面的 countSize 方法的返回类型就可以设计成 WordBean[],如下： public class PatternDemo { //此方法用来统计 content 中的英文单词个数， 请使用正则表达式来做，单词的正则表达式请自行编写， public int countWords(CharSequence content) { ... } //此方法返回一串固定的字符串，已写好，可以直接用。 public StringBuilder getContent() { //此方法的内容如下： StringBuilder builder = new StringBuilder(); builder.append("Hooray! It's snowing! It's time to make a snowman.James runs out. He makes a big pile of snow. He puts a big snowball on top. He adds a scarf and a hat. He adds an orange for the nose. He adds coal for the eyes and buttons.In the evening, James opens the door. What does he see? The snowman is moving! James invites him in. The snowman has never been inside a house. He says hello to the cat. He plays with paper towels.A moment later, the snowman takes James's hand and goes out.They go up, up, up into the air! They are flying! What a wonderful night!The next morning, James jumps out of bed. He runs to the door.He wants to thank the snowman. But he's gone."); // return builder; } //此方法统计出每个单词[不考虑大小写]出现的次数，数据结构请自行定义,设计如下： public ? countSize(CharSequence content) { //TODO ... } //注：int[]结构来存放结果 } public class WordBean { //属性 private String word; //单词 private int count; //出次 //TODO 请自行完成构造、getter/setter、toString、等相关方法 } public WordBean[] countSize(CharSequence content) { //TODO ... } 最后写一个调用者类，来测试你的实现，如下： public class UsePatternDemo() { public static void main(String[] args) { //TODO ... }

下面是一个实现了 countSize 方法和 WordBean 类的示例代码：

import java.util.HashMap;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class PatternDemo {
    public int countWords(CharSequence content) {
        // 定义单词的正则表达式
        String patternStr = "\\b\\w+\\b";
        Pattern pattern = Pattern.compile(patternStr);
        Matcher matcher = pattern.matcher(content);

        int count = 0;
        while (matcher.find()) {
            count++;
        }

        return count;
    }

    public WordBean[] countSize(CharSequence content) {
        // 定义单词的正则表达式
        String patternStr = "\\b\\w+\\b";
        Pattern pattern = Pattern.compile(patternStr);
        Matcher matcher = pattern.matcher(content);

        // 使用 Map 来统计每个单词的出现次数
        Map<String, Integer> wordCountMap = new HashMap<>();
        while (matcher.find()) {
            String word = matcher.group().toLowerCase();
            if (wordCountMap.containsKey(word)) {
                wordCountMap.put(word, wordCountMap.get(word) + 1);
            } else {
                wordCountMap.put(word, 1);
            }
        }

        // 将统计结果封装到 WordBean 数组中
        WordBean[] result = new WordBean[wordCountMap.size()];
        int i = 0;
        for (Map.Entry<String, Integer> entry : wordCountMap.entrySet()) {
            result[i++] = new WordBean(entry.getKey(), entry.getValue());
        }
        return result;
    }

    public StringBuilder getContent() {
        StringBuilder builder = new StringBuilder();
        builder.append("Hooray! It's snowing! It's time to make a snowman.James runs out. He makes a big pile of snow. He puts a big snowball on top. He adds a scarf and a hat. He adds an orange for the nose. He adds coal for the eyes and buttons.In the evening, James opens the door. What does he see? The snowman is moving! James invites him in. The snowman has never been inside a house. He says hello to the cat. He plays with paper towels.A moment later, the snowman takes James's hand and goes out.They go up, up, up into the air! They are flying! What a wonderful night!The next morning, James jumps out of bed. He runs to the door.He wants to thank the snowman. But he's gone.");
        return builder;
    }
}

public class WordBean {
    private String word;
    private int count;

    public WordBean(String word, int count) {
        this.word = word;
        this.count = count;
    }

    public String getWord() {
        return word;
    }

    public void setWord(String word) {
        this.word = word;
    }

    public int getCount() {
        return count;
    }

    public void setCount(int count) {
        this.count = count;
    }

    @Override
    public String toString() {
        return "WordBean{" +
                "word='" + word + '\'' +
                ", count=" + count +
                '}';
    }
}

public class UsePatternDemo {
    public static void main(String[] args) {
        PatternDemo patternDemo = new PatternDemo();
        StringBuilder content = patternDemo.getContent();
        WordBean[] result = patternDemo.countSize(content);
        for (WordBean wordBean : result) {
            System.out.println(wordBean);
        }
    }
}

在这个示例代码中，我们封装了一个 WordBean 类，用来表示单词和它的出现次数。在 countSize 方法中，我们使用正则表达式来匹配文本中的单词，并使用 HashMap 来统计每个单词的出现次数。最后，我们将统计结果封装到 WordBean 数组中返回。在调用者类 UsePatternDemo 中，我们可以测试我们的实现是否正确。