Strings and arrays

 character string ：
     It is simply understood as ： A string composed of several strings by a signature , It's called string 
     Official understanding ：
         A string is a string of data consisting of multiple characters ( Character sequence )
         A string can be thought of as an array of characters  ******

     Through observation API Find out ：
        1、String Represents a string . Belong to java.lang It's a bag , Therefore, there is no need to guide the package when using 
        2、String Class represents string . Java All string text in the program （ for example "abc" ） Are implemented as instances of this class .( object )
        3、 The string doesn't change ;  Their values cannot be changed after creation .
             Strings are constants , Once assigned , The string itself cannot be modified .

 Construction method ：
    public String()
    public String(byte[] bytes)
     Create a string object from a byte array 
    public String(byte[] bytes,int offset,int length)
     Convert a part of the byte array into a string 
    public String(char[] value)
     Convert a character array to a string 
//public String(char[] value,int index,int length)
// Convert part of the character array to a string 
   public String(char[] value,int offset,int count)
   public String(String original)

public class StringDemo1 {
    public static void main(String[] args) {
        //public String()
        String s = new String();
        System.out.println(s); //String Class toString()
        // Look at the length of the string 
        //public int length() Returns the length of this string .
        System.out.println(" character string s The length of is ：" + s.length()); // If there are no characters in the string , return 0
           //         character string s The length of is ：0
        System.out.println("=====================================================");
        //public String(byte[] bytes)  // Create a string object from a byte array 
        byte[] bytes = {97, 98, 99, 100, 101};
        String s2 = new String(bytes);
        System.out.println("s2: " + s2);//abcde
        System.out.println(" character string s2 The length of is ：" + s2.length());// character string s2 The length of is ：5

        System.out.println("=====================================================");
        //public String(byte[] bytes,int index,int length)
        // Convert a part of the byte array into a string 
        String s3 = new String(bytes, 1, 3);
        System.out.println("s3: " + s3);//bcd
        System.out.println(" character string s3 The length of is ：" + s3.length());//3

        System.out.println("=====================================================");
        //public String(char[] value)
        // Convert a character array to a string 
        char[] c = {'a', 'b', 'c', 'd', ' I ', ' Love ', ' feng ', ' carry ', ' No '};
        String s4 = new String(c);
        System.out.println("s4: " + s4);//abcd I love von Timo 
        System.out.println(" character string s4 The length of is ：" + s4.length());//9

        System.out.println("=====================================================");
        //public String(char[] value,int index,int length)
        // Convert part of the character array to a string 
        String s5 = new String(c, 4, 5);
        System.out.println("s5: " + s5);// I love von Timo 
        System.out.println(" character string s5 The length of is ：" + s5.length());//5

        System.out.println("=====================================================");
        //StringIndexOutOfBoundsException
//        String s6 = new String(c,4,10);
//        System.out.println("s6: "+s6);
//        System.out.println(" character string s5 The length of is ：" + s6.length());

        System.out.println("=====================================================");
        //public String(String original)
        String s7 = " Hello ";
        String s8 = new String(s7);
        System.out.println("s8: " + s8);// Hello 
        System.out.println(" character string s8 The length of is ：" + s8.length());//2


    }
}

ring(String original)