java字符编码 String和char

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本文链接： https://blog.csdn.net/u013501457/article/details/102661433

java字符编码

结合上图和下面的程序

public static void main(String[] args) {
        String s = "\uD835\uDD6B";
        print(s);
    }

    private static void print(String s) {
        System.out.println("s: "+s);
        System.out.println("s.length(): "+s.length());
        System.out.println("s.codePointCount(0,s.length()): "+s.codePointCount(0,s.length()));
        printBytes(s);
        printBytes(s,"GBK");
        printBytes(s,"UTF-8");
        printBytes(s,"UTF-16");
        printChars(s);
    }

    private static void printBytes(String s) {
        byte[] bytes = s.getBytes();
        System.out.print(String.format("%s: ","默认编码"));
        for(byte b :bytes) {
            System.out.printf(String.format("%02x ",b));
        }
        System.out.println();
    }

    private static void printBytes(String s,String charset) {
        byte[] bytes = new byte[0];
        try {
            bytes = s.getBytes(charset);
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        System.out.print(String.format("%s: ",charset));
        for(byte b :bytes) {
            System.out.printf(String.format("%02x ",b));
        }
        System.out.println();
    }

    private static void printChars(String s) {
        char[] bytes = s.toCharArray();
        System.out.print(String.format("%s: ","char底层"));
        for(char b :bytes) {
            System.out.printf(Integer.toHexString(b)+" ");
        }
        System.out.println();
    }

结果:

1. .java文件编码不影响程序运行时的字符编码
2. 任何编码格式的java文件,转换为class二进制时,字符串常量都会转换为UTF-8字节
3. 程序运行时,加载class,将UTF-8字符串常量转换为UTF-16编码保存在内存中,以char[]的形式保存UTF-16编码
4. String.length()获得的是UTF-16的char[]数组的长度,UTF-16存在2字节字符和4字节字符,2字节字符占用1个char,4字节字符占用2个char,所以,length() 不等于 字符数
5. String.codePointCount()获得的是对UTF-16的char[]数组对应的字符数(码点) 也就是真实的字符数
6. String.getBytes()时,将UTF-16的char[]转化为指定的编码字节数组,如果没有指定,使用UTF-8
7. java中 char[]的默认编码格式为UTF-16