[indexof] [lastIndexOf] [split] [substring] usage details

1. IndexOf() and lastIndexOf() What's the difference ？ 

indexOf() and lastIndexOf() It's all index files

indexOf() Is to check the first occurrence of a specified string in the string （ Index value ）（ From left to right ）

lastIndexOf() Is to check the position of a specified string at the last occurrence of the string （ Index value ）（ From left to right ）
lastIndexOf() The method is to search from back to front , But the returned position is the same as before .

let arr = [1, 2, 4, 4, 5, 3, 3, 7, 8, 5]

   console.log(arr.indexOf(4));  // 2
   console.log(arr.lastIndexOf(4));  // 3

2. Java String indexOf() Method

indexOf() The method has the following four forms ：

• public int indexOf(int ch):  Returns the index of the first occurrence of the specified character in the string , If there is no such character in this string , Then return to -1.

• public int indexOf(int ch, int fromIndex):  Return from fromIndex Position starts to find the index of the first occurrence of the specified character in the string , If there is no such character in this string , Then return to -1.

• int indexOf(String str):  Returns the index of the first occurrence of the specified character in the string , If there is no such character in this string , Then return to -1.

• int indexOf(String str, int fromIndex):  Return from fromIndex Position starts to find the index of the first occurrence of the specified character in the string , If there is no such character in this string , Then return to -1.

public class Main {
    public static void main(String args[]) {
        String string = "aaa456ac";  
        // Finds the subscript where the specified character is in the string . In, it returns the subscript of the string ; If not, return to -1. 
        System.out.println(string.indexOf("b")); // indexOf(String str);  Return results ：-1,"b" non-existent  
 
        //  Start at the fourth character position and continue to find , Contains the current location  
        System.out.println(string.indexOf("a",3));//indexOf(String str, int fromIndex);  Return results ：6 
 
        //（ The difference from before ： The above parameter is  String  type , The following parameters are  int  type ） Reference data ：a-97,b-98,c-99 
 
        //  Find whether the specified character exists from the beginning  
        System.out.println(string.indexOf(99));//indexOf(int ch); Return results ：7 
        System.out.println(string.indexOf('c'));//indexOf(int ch); Return results ：7 
 
        // from fromIndex lookup ch, This is a character variable , It's not a string . character a The corresponding number is 97. 
        System.out.println(string.indexOf(97,3));//indexOf(int ch, int fromIndex);  Return results ：6 
        System.out.println(string.indexOf('a',3));//indexOf(int ch, int fromIndex);  Return results ：6 
    }
}


//  Output results 
// -1
// 6
// 7
// 7
// 6
// 6

3. Java ArrayList lastIndexOf() Method  

lastIndexOf() Method returns the position of the last occurrence of the specified element in the dynamic array .

lastIndexOf() The syntax of the method is ：arraylist.lastIndexOf(Object obj)

class Main {
    public static void main(String[] args){

        //  Create an array 
        ArrayList<String> sites = new ArrayList<>();

        sites.add("Google");
        sites.add("Runoob");
        sites.add("Taobao");
        sites.add("Runoob");
        System.out.println(" Website list : " + sites);


        //  obtain  Runoob  The last location 
        int position1 = sites.lastIndexOf("Runoob");
        System.out.println("Runoob  The last place : " + position1);

        // Wiki  be not in  arraylist  in 
        //  return  -1
        int position2 = sites.lastIndexOf("Wiki");
        System.out.println("Wiki  The last place : " + position2);
    }
}

//  The output of the above program is ：

//  Website list : [Google, Runoob, Taobao, Runoob]
// Runoob  The last place : 3
// Wiki  The last place : -1

4. split() Method splits the string by matching the given regular expression

Be careful ： . 、 $、 |  and  *  Wait for escape characters , Must add  \\.

Be careful ： Multiple separators , It can be used  |  As a hyphen .

grammar

public String[] split(String regex, int limit)

Parameters

• regex -- Regular expression separator .

• limit -- The number of split copies .

public class Test {
    public static void main(String args[]) {
        String str = new String("Welcome-to-Runoob");
 
        System.out.println("-  The separator returns the value  :" );
        for (String retval: str.split("-")){
            System.out.println(retval);
        }
 
        System.out.println("");
        System.out.println("-  The separator sets the number of splits and the return value  :" );
        for (String retval: str.split("-", 2)){
            System.out.println(retval);
        }
 
        System.out.println("");
        String str2 = new String("www.runoob.com");
        System.out.println(" Escape character return value  :" );
        for (String retval: str2.split("\\.", 3)){
            System.out.println(retval);
        }
 
        System.out.println("");
        String str3 = new String("acount=? and uu =? or n=?");
        System.out.println(" Multiple separator return values  :" );
        for (String retval: str3.split("and|or")){
            System.out.println(retval);
        }
    }
}

The execution result of the above procedure is ：

The separator returns the value :
        Welcome
        to
        Runoob

The separator sets the number of splits and the return value :
        Welcome
        to-Runoob

Escape character return value :
        www
        runoob
        com

Multiple separator return values :
        acount=?
        uu =?
        n=?

5. String Of substring（） Used to intercept strings

substring（） Substring used to return a string , That is, the function of intercepting strings .

substring（） Common overloading methods are as follows ：

substring（int beginIndex,int endIndex） Return subscript from beginIndex Start （ Include ）, To endIndex（ barring ） The ending substring .

               eg： String str = "http://www.oracle.com";

                       String subStr = str.substring(11, 17);

                       System.out.println(subStr); // oracle

substring（int beginIndex） Return subscript from beginIndex Start （ Include ）, Substring to the end of the string .

             eg： String str = "http://www.oracle.com";

                       String subStr = str.substring(7);

                      System.out.println(subStr); // www.oracle.com