String中编码和解码的问题你了解多少呢?

一: 编码的方法

getBytes()方法
public byte] getBytes();

此方法根据java命令运行时参数file.encoding设置的编码表进行编码的。(file.encoding在idea中一般设置默认是UTF-8,但是在电脑系统中就是用的GBK)

String str =“黑马";
byte[] bytes = str.getBytes();  //对"黑马"进行编码使用idea中默认的UTF-8进行编码.
//byte中高位为1则为负数
system. out.println(Array's.tostring(bytes));//[-23,-69,-111，-23，-87，-84]

查看getBytes()源码

 

 IDEA中验证: (idea中的编码格式也是可以改变的)

String propertya = System.getProperty("file.encoding");
system.out.println(property);  //UTE-8  可见idea中系统默认的环境为UTF-8
string str=“黑马";
byte[] bytes.=.str.getBytes()   
system.out.println(Arrays.toString(bytes));   //[-23,-69,-111,-23,-87,-84]

 电脑系统验证

 这个编码格式是可以改变的

二: 解码的方法

string(byte[] code)
public String(byte[] code);   //此方法根据file.encoding进行解码 (idea中默认是UTF-8编码)

1: 不乱码的情况

public static void main( string[] args) throws Exception{
   string str ="黑马";
   byte[] bytes = str.getBytes("UTF-8");
   System.out.println(Arrays.toString(bytes)); //[-23, -69， -111，-23，-87，-84]

   byte[] gbks = str.getBytes("GBK");
   system.out.println(Arrays.tostring(gbks)); //[-70, -38,-62，-19]
}

public static void main(String[ ] args) throws Exception{
    byte[] bytes =f-23，-69，-111,-23，-87,-84};
    string str = new String(bytes); // file.encoding(idea默认是UTF-8)
    system.out.println(str);//黑马

    string str1 = new String(bytes, "UTF-8" );
    system.out.println(str1); //黑马

    byte[] bys = {-70,-38,-62y -19};
    String str2 = new string(bys, charsetName: "GBK");
    system.out.println(str2); //黑马
}

2: 乱码的情况(可逆的)

public static void main(string[] args) throws Exception{
    string str =“黑马";
    byte[] gbks = str.getBytes( charsetName: "GBK");  //对"用GBK对黑马进行编码"
    system.out.println(Arrays.toString(gbks)); //[-70， -38，-62，-19]I

    string s = new string(gbks, charsetName: "UTF-8"); //用UTF-8对gbks数组进行解码
    system.out.println(s); //???? 乱码

    string s1 = new string(gbks, charsetName: "GBK");
    system.out.println(s1); //黑马
}

3: 乱码的情况(不可逆的)

public static void main(string[] args) throws Exception{
      string str ="黑马";
      byte[] bytes = str.getBytes( charsetName: "IS0-8859-1"); // ?? 63 63(在ASCII码中代表?)
      system.out.println(Arrays.tostring(bytes)); //[63，63]

      string s = new String(bytes, charsetName: "IS0-8859-1");
      system.out.println(s); // ? ? 
     //原因(因为黑马在iso-8859-1中是不存在对应编码的,所以被当做?处理了,从本质上改变了它的字节, 
       所以后面无论以什么来解码它都是无效的)

      string s1 = new String(bytes, charsetName: "GBK");
      system. out.print1n(s1); // ? ?

      string s2 = new String(bytes, charsetName: "UTF-8"); 
      System.out.println(s2); // ? ?
}

string str = "\uD842\UDFB7"; 
//代表中文"吉(上短下长,因为打不出来)"在GBK中也不存在,所以编码的时候被当做?来处理了
byte[] gbks = str.getBytes( charsetName: "GBK");
system.out.print1n(Arrays.tostring(gbks)); //[63] 

string s = new string(gbks , charsetName: "gbk");
system.out.println(s); //?

string str = "♥";    
byte[] gbks = str.getBytes( charsetName: "GBK");
system.out.println( Arrays.toString(gbks)); //[63]   
//跟前面一样的道理

String s = new String(gbks, charsetName:"gbk"");
system.out.println(s);   //?

大家在思考一下这个问题.

public static vo1d main( str1ng[] args) throws Except1on{
    string s =“黑马";
    byte[] bytes = s.getBytes( charsetName: "GBK");
    system.out.println(Arrays.toString(bytes)); //[-70, -38, -62， -19]

    string str = new String(bytes, charsetName: "UTF-8");
    system.out.println(str); //实心????(当没有办法解析或者解析不了的时候)    //(注意:实心?在UTF-8中有对应的编码)

    byte[] bytes1 = str.getBytes( charsetName: "UTF-8");
    system.out.println(Arrays.toString(bytes1)); //[-17, -65, -67，-17，-65, -67，-17,
-65,-67,-17，-65，-67]

    string str1 = new String(bytes1, charsetName: "GBK");
    system.out.println(str1); //银斤拷银斤拷

ISO8859-1解决上述场景所遇到的问题

String s =“黑马";
byte[] bytes = s.getBytes( charsetName: "GBK");
system.out.println(Arrays.tostring(bytes)); //[-70,-38，-62， -19]

String str = new string(bytes, charsetName: "IS0-8859-1"); //关键在于:(一个字节对应一个字符)
system.out.println(str): //-oii

byte[] bytes1 = str.getBytes( charsetName: "ISO-8859-1");
system.out.println(Arrays.tostring(bytes1)); //[-70，-38, -62，-19]

string str1 = new String(bytes1, charsetName: "GBK");
system.out.println(str1); //黑马