CharSequence源码分析

CharSequence是一个接口，表示一个char值的可读序列，此接口为多种char序列提供统一的、只读的通道。既然是接口，就不能通过new来进行赋值，只能通过以下方式赋值：

CharSequence cs = "ss";

该接口有4个常规方法和两个default方法（这两个暂时先不分析了）。

    int length();  
    char charAt(int index);
    CharSequence subSequence(int start, int end);
    public String toString();
     
     *
     * @return an IntStream of char values from this sequence
     * @since 1.8
     */
    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);
    }
　　　　
     *
     * @return an IntStream of Unicode code points from this sequence
     * @since 1.8
     */
    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);
    }

测试：

package com.test;

public class Test {
    @org.junit.Test
    public void test(){
        CharSequence cs = "welcome";
        System.out.println("字符序列的长度："+cs.length());
        System.out.println("截取第一位字符（原字符序列不改变）："+cs.subSequence(0, 2));
        System.out.println("字符序列转换成字符串表示："+cs.toString());
        System.out.println("返回第一个字符："+cs.charAt(6));
    }
}

结果：