Technology

Understanding Substring in Java: A Basic Guide

In this text, we are going to allow you to perceive substrings in Java. We is not going to solely offer you a theoretical clarification but in addition offer you actual code examples that will help you visualize. We will educate you the right way to create substrings and allow you to discover substrings inside a string.

But earlier than studying them, we’ve got to have the fundamentals of substrings.

What are strings and substrings?

In the context of Java, a string represents a sequence of characters. Every string in Java is an object. A string in Java can include characters, symbols, and even whitespace. On the opposite hand, a substring in Java is a portion or a subset of a Java string. 

For instance, “Geek” is a substring of “GeekFlare”. Substrings allow you to get a particular a part of a string.

If you’ve gotten the title “John Doe” and also you need solely the primary title “John”, you possibly can simply get it with substrings. Moreover, contemplating you’ve gotten an inventory of names “John, Jack, Jolly” and also you need to discover out if “John” is in it, you may also do it with substrings. These are solely mere examples. We can use substrings in varied operations as soon as we perceive them.

As we are actually conscious of the idea of substrings in Java, now, let’s get to know the right way to create and work with substrings in Java.

#1. Using the ‘substring()’ methodology

The ‘substring()’ methodology lets us create substrings very simply. It takes as much as two parameters as enter – beginIndex or each beginIndex and finishIndex and returns us the substring we wish.

Depending on the variety of parameters, we are able to use it in two methods. Now, let’s get to study them in element.

substring(int beginIndex)

To begin, we are able to use the tactic in ‘substring(startIndex)’ type. Here, this methodology takes an integer worth as enter, the place the enter is the beginning place of the substring. It returns a string ranging from the offered begin index until the tip of the unique string.

As an instance, let’s take a look at the next code:

public class Substrings{    
    public static void primary(String args[]){    
    String str="GeekFlare";    
    System.out.println("Given String: " + str);  
    System.out.println("Substring: " +str.substring(4)); //index of strings begin from 0
    }  
   }

OUTPUT:

Given String: GeekFlare
Substring: Flare

From the output, we see for the enter string is “GeekFlare”, and the return worth is the substring “Flare”. It makes a substring from the given index (4), that’s, from place 5 to the tip of the string.

substring(int beginIndex, int finishIndex)

This is one other approach to make use of the substring methodology of the String class. We can go two integers to the substring methodology. A begin index and an finish index. To use this, we’ve got to make use of the tactic in the ‘substring(startIndex,endIndex)’ format.

To perceive it additional, let’s take a look at some instance code:

public class Substrings{    
    public static void primary(String args[]){    
    String str="GeekFlareFans";    
    System.out.println("Given String: " + str);  
    System.out.println("Substring: " +str.substring(4,9));  //You get a substring ranging from index no. 4 to index 8.

    }  
   }

OUTPUT:

Given String: GeekFlareFollowers
Substring: Flare

As we are able to see, given the string “GeekFlareFans”, it outputs the substring “Flare”. We gave the beginning index of 4 and the tip index of 9. It begins from the aspect with an index of 4 and ends earlier than 9. We have to notice that it doesn’t print the aspect with the tip index. It offers us a substring that features all parts until the tip index however excludes the aspect with the tip index.

#2. Using the ‘split()’ methodology

The ‘split()’ is one other methodology of the String class in Java that helps us create a substring. It is beneficial when a number of items of data are saved inside one string with a typical separator character.

The syntax mentions the time period “regex” which can appear a bit of intimidating to you, so let’s perceive what regex is earlier than continuing. Regex is the brief time period for “Regular Expressions”. A regex is a sequence of characters that describes a sample inside a string or textual content. In the context of the break up methodology, the regex is our separator.

The ‘split()’ methodology can take as much as two variables as enter, they’re a regex string and a restrict integer. The regex is the separator, which, when discovered, outcomes in splitting the unique string into 2 components – the half earlier than the regex and the half after the regex.

For instance, assume you are attempting to separate the string “abcdef” with “bcd” as regex. We would get the substrings “a” and “ef” because the outcome.

The methodology returns an array with the separated strings. We can both specify solely the regex or each the regex and the restrict. Let’s get to know concerning the a number of methods to name this methodology one after the other.

break up(String regex)

The first methodology receives solely the regex string in the ‘split(regex)’ format. It doesn’t have a restrict variable; subsequently returns all of the separated substrings in an array. 

Let’s get a transparent understanding with some code:

public class Substrings{    
    public static void primary(String args[]){    
    String str="Geek%Flare";
    String[] substrings=str.break up("%");
    System.out.println("Given String: " + str);
    System.out.println("First Substring: " + substrings[0]);
    System.out.println("Second Substring: " + substrings[1]);
     
    }  
}

OUTPUT:

Given String: Geek%Flare
First Substring: Geek
Second Substring: Flare

As we observe from the code, the given string has a separator regex “%”. It doesn’t should be a single character, it may be any string with any variety of characters. The ‘split()’ methodology ignores this regex and offers us all of the strings that had been separated by this regex. The substrings are saved inside an array.

In the code, the given string is “Geek%Flare”. So, we get an array with two parts in it, that are “Geek” and “Flare”. We later accessed them with their respective indices, that are 0,1 respectively, and we printed “Geek” and “Flare” to the console.

Here we must also be aware that if no parameters are handed to the tactic, it’s going to merely throw an error. But if we give an empty string (“”) as a regex, we are going to get each particular person character as a substring. Let’s take a look at the instance to visualise.

import java.util.Arrays;

public class Substrings{    
    public static void primary(String args[]){    
    String str="Geek%Flare";
    String[] substrings=str.break up("");
    System.out.println(Arrays.toString(substrings));
     
    }  
}

OUTPUT:

[G, e, e, k, %, F, l, a, r, e]

From the instance, it’s obvious because the regex parameter is an empty string, it returns all of the characters as separate substrings, and we are able to clearly see this by printing the output array of the ‘split()’ methodology.

break up(String regex,int restrict)

With the second variant of this methodology, we get extra management over the output, and we are able to additional fine-tune the output of the ‘split()’ methodology. Here, the ‘split()’ methodology takes two variables as enter. In this case, together with the regex, we additionally give a restrict parameter in the required format of ‘split(regex, limit)’. 

The ‘limit’ is the variety of ensuing strings which are output. Depending on the worth of the restrict, there will be three potentialities:

Case 1: If restrict>0, the ensuing array would include the output, however it will apply the break up (limit-1) occasions at most. Here, the ensuing array wouldn’t include extra parts than the required restrict, and all of the leftover string that isn’t break up could be saved because it was. Let’s make it simpler to know with some code.

import java.util.Arrays;

public class Substrings{    
    public static void primary(String args[]){    
    String str="Geek%Flare%is%the%best";
    String[] substrings=str.break up("%",2);
    System.out.println(Arrays.toString(substrings));
     
    }  
}

OUTPUT:

[Geek, Flare%is%the%best]

See in the output how there are solely two parts in the outcome array which is the quantity given in the restrict parameter. Also, discover that the break up is utilized just one time, so (limit-1) occasions. 

However,  if the regex is there two occasions in a row (“%%”), it will have empty substrings. Look at this little bit of code to know it higher.

import java.util.Arrays;

public class Substrings{    
    public static void primary(String args[]){    
    String str="Geek%Flare%is%%the%best%%%";
    String[] substrings=str.break up("%",5);
    System.out.println(Arrays.toString(substrings));
     
    }  
}

OUTPUT:

[Geek, Flare, is, , the%best%%%]

Basically, if  “%” is adopted by one other “%” or the tip of the string, it transforms into an empty substring. 

Case 2: If restrict<0, the break up motion could be utilized as many occasions it’s potential with no restrict to the array measurement, however the array would include empty substrings if the regex is there two occasions in a row (“%%”).

import java.util.Arrays;

public class Substrings{    
    public static void primary(String args[]){    
    String str="Geek%Flare%is%%the%best%%%";
    String[] substrings=str.break up("%",-1);
    System.out.println(Arrays.toString(substrings));
     
    }  
}

OUTPUT:

[Geek, Flare, is, , the, best, , , ]

From the output, it’s obvious that the break up is utilized as many occasions as potential, and likewise there are empty substrings current. 

Case 3: If restrict=0, the break up motion would even be utilized as many occasions as potential, however right here all of the empty substrings on the finish of the string could be discarded from the array.

import java.util.Arrays;

public class Substrings{    
    public static void primary(String args[]){    
    String str="Geek%Flare%is%%the%best%%%";
    String[] substrings=str.break up("%",0);
    System.out.println(Arrays.toString(substrings));
     
    }  
}

OUTPUT:

[Geek, Flare, is, , the, best]

We can see that the output is sort of related between when restrict=-1 and when restrict=0, however there aren’t any trailing empty substrings. In different phrases, the empty substrings on the finish of the substring array are ignored.

Also be aware that if the regex isn’t current in the string, it returns the complete unique string because the outcome.

Find if a String Contains a Substring

Besides creating substrings from current strings, we are able to additionally specify a substring and discover out if that substring is existent inside a string. This is a fast and simple approach to question a substring, and that is helpful in many use instances. But how can we do it? Various strategies might help us obtain this. Let’s undergo them one after the other.

Using ‘contains()’ methodology:

We can very simply discover the existence of a substring with the ‘contains()’ methodology. This methodology of the String Class takes a string as enter, which is our substring, and returns a boolean worth checking if the substring is contained in the string or not. This methodology can be utilized inside if-else blocks, unary operators, and varied different locations to implement complicated logic.

Let’s get to find out about this methodology a bit of extra.

public class Substrings{    
    public static void primary(String args[]){    
    String str="GeekFlare";    
    System.out.println("Does it contain Flare? n"+ str.incorporates("Flare"));  
    }  
}

OUTPUT:

Does it include Flare? 
true

The code checks the string “GeekFlare” for the phrase “Flare”, and on discovering it efficiently, it returns a boolean “true”, subsequently confirming the existence of the substring.

public class Substrings{    
    public static void primary(String args[]){    
    String str="GeekFlare";    
    System.out.println("Does it contain Flare? n"+ str.incorporates("Flare1"));  
    }  
}

OUTPUT:

Does it include Flare? 
false

From the instance, we perceive if the substring isn’t contained in the string, the tactic will return false to indicate its non-existence. So we will be simply certain if the substring exists.

Finding the Position of a Substring

#1. Using ‘indexOf()’:

The ‘indexOf()’ methodology can be utilized to seek out the existence of a substring and in addition to discover its index. The methodology takes as enter a string or a personality and offers us the place of its first incidence. But it’s only capable of give us the index of the primary incidence and might’t affirm if different occurrences of this exist. Another factor to notice right here, if the substring doesn’t exist, the tactic returns -1.

So let’s discover this methodology a bit of extra.

public class Substrings{    
    public static void primary(String args[]){    
    String str="GeekFlareGeekFlare";    
    System.out.println("Index of Flare: "+ str.indexOf("Flare"));  
    }  
}

OUTPUT:

Index of Flare: 4

Here in the instance, the primary incidence of the substring “Flare” begins from index 4 in the string “GeekFlareGeekFlare”. So, as anticipated, the perform returned the index.

#2. Using ‘lastIndexOf()’:

‘lastIndexOf()’ is similar to ‘indexOf()’. Both of those strategies take as enter the substring and return the index of its place. It even has the identical return worth when it will possibly’t discover the substring in the required string. Both of those strategies return -1 for an unsuccessful discover.

But whereas ‘indexOf()’ returns the index of the primary incidence of the substring, ‘lastIndexOf()’ returns the final incidence.

Let’s see it in motion via code:

public class Substrings{    
    public static void primary(String args[]){    
    String str="GeekFlareGeekFlare";    
    System.out.println("Last index of Flare: "+ str.finalIndexOf("Flare"));  
    }  
}

OUTPUT:

Last index of Flare:13

Observing this output, we perceive that the tactic ‘lastIndexOf()’ behaves as anticipated and we get the index of the final incidence of the substring “Flare” in the string “GeekFlareGeekFlare”.

FAQs

How to make use of the ‘split()’ methodology to create non-empty substrings?

If there are a number of regex cases of the regex string in the primary string one after one other(“Hello%%Hi”, the place regex is “%”), the ‘split()’ methodology considers the primary occasion as a break character, and the remainder offers the output of an empty string. To mitigate this, we are able to specify the restrict parameter as 0. Hence it’s going to give solely non-empty strings as output.

Does ‘indexOf()’ return indexes of all of the cases of a substring?

No, ‘indexOf()’ doesn’t return indexes of all of the cases of a substring. With ‘indexOf()’, we get an integer return worth containing the index of the primary incidence of the substring. But if it will possibly’t discover the substring, the tactic will return -1.

What does the ‘substring()’ methodology return if the given indexes dont exist in the string?

If the given start index and the end index don’t exist in the string, the compiler will throw an error. The error ought to have “java.lang.StringIndexOutOfBoundsException: ” and it’ll merely not execute.

Conclusion

In this text, we mentioned varied strategies and necessities to get began with substrings. We mentioned making a substring and checking the existence of a substring inside a string. This will provide you with a greater understanding of the right way to work with substrings. Follow the examples and apply extra to get an intensive understanding of substrings.

Next, chances are you’ll test our checklist of Java interview questions.

Vikash Gorayan

Vikash Gorayan is a technology enthusiast with a passion for gadgets and product management. He is constantly seeking new opportunities to learn and grow in his field.

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