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Java String substring()

The Java String class substring() method returns a part of the string.

We pass beginIndex and endIndex number position in the Java substring method where beginIndex is inclusive, and endIndex is exclusive. In other words, the beginIndex starts from 0, whereas the endIndex starts from 1.

There are two types of substring methods in Java string.

Signature

public String substring(int startIndex)  // type - 1
and  
public String substring(int startIndex, int endIndex)  // type - 2

If we don't specify endIndex, the method will return all the characters from startIndex.

Parameters

startIndex : starting index is inclusive

endIndex : ending index is exclusive

Returns

specified string

Exception Throws

StringIndexOutOfBoundsException is thrown when any one of the following conditions is met.

if the start index is negative value
end index is lower than starting index.
Either starting or ending index is greater than the total number of characters present in the string.

Internal implementation substring(int beginIndex)

public String substring(int beginIndex) {  
       if (beginIndex < 0) {  
           throw new StringIndexOutOfBoundsException(beginIndex);  
       }  
       int subLen = value.length - beginIndex;  
       if (subLen < 0) {  
           throw new StringIndexOutOfBoundsException(subLen);  
       }  
       return (beginIndex == 0) ? this : new String(value, beginIndex, subLen);  
   } 

Internal implementation substring(int beginIndex, int endIndex)

public String substring(int beginIndex, int endIndex) 
{
if (beginIndex < 0) 
{
throw new StringIndexOutOfBoundsException(beginIndex);
}
if (endIndex > value.length) 
{
throw new StringIndexOutOfBoundsException(endIndex);
}
int subLen = endIndex - beginIndex;
if (subLen < 0) 
{
throw new StringIndexOutOfBoundsException(subLen);
}
return ((beginIndex == 0) && (endIndex == value.length)) ? this : new String(value, beginIndex, subLen);
}

Java String substring() method example

FileName: SubstringExample.java

public class SubstringExample{
public static void main(String args[]){
String s1="javatpoint";
System.out.println(s1.substring(2,4));//returns va
System.out.println(s1.substring(2));//returns vatpoint
}}

Output:

va
vatpoint

Java String substring() Method Example 2

FileName: SubstringExample2.java

public class SubstringExample2 {
	public static void main(String[] args) {
		String s1="Javatpoint";  
		String substr = s1.substring(0); // Starts with 0 and goes to end
		System.out.println(substr);
		String substr2 = s1.substring(5,10); // Starts from 5 and goes to 10
		System.out.println(substr2);  
		String substr3 = s1.substring(5,15); // Returns Exception
	}
}

Output:

Javatpoint
point
Exception in thread "main" java.lang.StringIndexOutOfBoundsException: begin 5, end 15, length 10

Applications of substring() Method

1) The substring() method can be used to do some prefix or suffix extraction. For example, we can have a list of names, and it is required to filter out names with surname as "singh". The following program shows the same.

FileName: SubstringExample3.java

public class SubstringExample3 
{
// main method
public static void main(String argvs[])
{
String str[] =
{
"Praveen Kumar",
"Yuvraj Singh",
"Harbhajan Singh",
"Gurjit Singh",
"Virat Kohli",
"Rohit Sharma",
"Sandeep Singh",
"Milkha Singh"
};

String surName = "Singh";
int surNameSize = surName.length();

int size = str.length;

for(int j = 0; j < size; j++)
{
    int length = str[j].length();
    // extracting the surname
    String subStr = str[j].substring(length - surNameSize);
    
    // checks whether the surname is equal to "Singh" or not
    if(subStr.equals(surName))
    {
        System.out.println(str[j]);
    }
}

}
}

Output:

Yuvraj Singh
Harbhajan Singh
Gurjit Singh
Sandeep Singh
Milkha Singh

2) The substring() method can also be used to check whether a string is a palindrome or not.

FileName: SubstringExample4.java

public class SubstringExample4 
{
public boolean isPalindrome(String str)
{
int size = str.length();

// handling the base case
if(size == 0 || size == 1)
{
// an empty string 
// or a string of only one character 
// is always a palindrome
return true;
}
String f = str.substring(0, 1);
String l = str.substring(size - 1);
// comparing first and the last character of the string
if(l.equals(f))
{
// recursively finding the solution using the substring() method
// reducing the number of characters of the by 2 for the next recursion
return isPalindrome(str.substring(1, size - 1));
}
return false;
}
// main method
public static void main(String argvs[])
{
// instantiating the class SubstringExample4 
SubstringExample4 obj = new SubstringExample4();
String str[] =
{
"madam",
"rock",
"eye",
"noon",
"kill"
};
int size = str.length;

for(int j = 0; j < size; j++)
{
if(obj.isPalindrome(str[j]))
{
System.out.println(str[j] + " is a palindrome.");
}
else
{
System.out.println(str[j] + " is not a palindrome.");
}
}
}
}

Output:

madam is a palindrome.
rock is not a palindrome.
eye is a palindrome.
noon is a palindrome.
kill is not a palindrome.

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