Summary of search methods for substrings in Java strings

There are four methods for searching substrings in strings in Java, as follows:
1. int indexOf(String str): Returns the index of the first occurrence of the specified substring in this string.
2. int indexOf(String str, int startIndex): Starting from the specified index, return the index of the first occurrence of the specified substring in this string.
3. int lastIndexOf(String str): Returns the index of the specified substring that appears on the rightmost side of this string.
4. int lastIndexOf(String str, int startIndex): Search backward from the specified index and return the index of the last occurrence of the specified substring in this string.

indexof() usage instructions

indexof()

Returns the character position of the first occurrence of the substring in the String object.

string.indexOf(subString[, startIndex])

Parameters

string

Required. String object or literal.

subString Required.

The substring to be found in the String object.

starIndex Optional.

This integer value indicates the index within the String object to start searching. If omitted, the search is from the beginning of the string.

Description
The indexOf method returns an integer value indicating the starting position of the substring within the String object. If the substring is not found, -1 is returned.

If startindex is a negative number, startindex is treated as zero. If it is greater than the largest character position index, it is treated as the largest possible index.

Perform the search from left to right. Otherwise, the method is the same as lastIndexOf.

Example
The following example illustrates the use of the indexOf method.

function IndexDemo(str2){
var str1 = "BABEBIBOBUBABEBIBOBU"
var s = str1.indexOf(str2);
return(s);
}

java finds the number of substrings in a string
1. Use the indexof method:

public class Test11
{
 
 private static int counter = 0;
 /**
 * @param args
 */
 public static void main(String[] args)
 {
 String str ="sdSS**&HGJhadHCASch& ^^";
 int i = stringNumbers(str);
 System.out.println(i);
 }
  
 public static int stringNumbers(String str)
 {
 if (str.indexOf("java")==-1)
 {
 return 0;
 }
 else if(str.indexOf("java") != -1)
 {
 counter++;
 stringNumbers(str.substring(str.indexOf("java")+4));
 return counter;
 }
 return 0;
 }
}

2. If the substring is not a string with the same beginning and end, it can also be implemented like this:

if(str.indexOf("java") != -1)
 {
 String[] str1 = str.split("java");
 System.out.println(str1.length-1);
 }
 else
 {
 System.out.println(0);
 }

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