Java源码赏析（六）Java String 三顾

在大致了解了String之后，可能有的读者发现了，我们并没有谈到CharSequence接口。

原因是在这一节，CharSequence要和StringBuilder（Java1.5）、StringBuffer（Java1.0）一起讨论。

package java.lang;

import java.util.NoSuchElementException;
import java.util.PrimitiveIterator;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.IntConsumer;
import java.util.stream.IntStream;
import java.util.stream.StreamSupport;

/**
 * 
 */
public interface CharSequence {

    /**
     * 返回字符串长度
     */
    int length();

    /**
     * 返回索引位置的字符
     */
    char charAt(int index);

    /**
     *   返回索引位置的子串
     */
    CharSequence subSequence(int start, int end);

    /**
     * 转化为String
     */
    public String toString();

    /**
     * 转化为int流
     */
    public default IntStream chars() {
        class CharIterator implements PrimitiveIterator.OfInt {
            int cur = 0;

            public boolean hasNext() {
                return cur < length();
            }

            public int nextInt() {
                if (hasNext()) {
                    return charAt(cur++);
                } else {
                    throw new NoSuchElementException();
                }
            }

            @Override
            public void forEachRemaining(IntConsumer block) {
                for (; cur < length(); cur++) {
                    block.accept(charAt(cur));
                }
            }
        }

        return StreamSupport.intStream(() ->
                Spliterators.spliterator(
                        new CharIterator(),
                        length(),
                        Spliterator.ORDERED),
                Spliterator.SUBSIZED | Spliterator.SIZED | Spliterator.ORDERED,
                false);
    }

    /**
     * 转化为int流
     */
    public default IntStream codePoints() {
        class CodePointIterator implements PrimitiveIterator.OfInt {
            int cur = 0;

            @Override
            public void forEachRemaining(IntConsumer block) {
                final int length = length();
                int i = cur;
                try {
                    while (i < length) {
                        char c1 = charAt(i++);
                        if (!Character.isHighSurrogate(c1) || i >= length) {
                            block.accept(c1);
                        } else {
                            char c2 = charAt(i);
                            if (Character.isLowSurrogate(c2)) {
                                i++;
                                block.accept(Character.toCodePoint(c1, c2));
                            } else {
                                block.accept(c1);
                            }
                        }
                    }
                } finally {
                    cur = i;
                }
            }

            public boolean hasNext() {
                return cur < length();
            }

            public int nextInt() {
                final int length = length();

                if (cur >= length) {
                    throw new NoSuchElementException();
                }
                char c1 = charAt(cur++);
                if (Character.isHighSurrogate(c1) && cur < length) {
                    char c2 = charAt(cur);
                    if (Character.isLowSurrogate(c2)) {
                        cur++;
                        return Character.toCodePoint(c1, c2);
                    }
                }
                return c1;
            }
        }

        return StreamSupport.intStream(() ->
                Spliterators.spliteratorUnknownSize(
                        new CodePointIterator(),
                        Spliterator.ORDERED),
                Spliterator.ORDERED,
                false);
    }
}

chars、codePoints是Java8的新增方法，主要用于int流操作，下面举个例子

//判断字符序列是否存在空格
boolean containsWhitespaces(CharSequence actual) {
    return actual.chars().anyMatch(Character::isWhitespace);
}

//判断字符序列不为空，而且存在空格
public static boolean containsWhitespace(String str) {
    return Objects.nonNull(str) && str.codePoints().anyMatch(Character::isWhitespace);
}

StringBuffer（线程安全）和StringBuilder（线程不安全）都是可变字符串
未完待续