String Methods In Java

In this article, we will discuss the most commonly used Java string methods with examples.

In Java, strings are a commonly used data type and the String class offers a set of built-in methods to manipulate strings

Java String Methods

The class String provides a collection of predefined methods that can be utilized to manipulate strings.

Java String Method charAt()

Characters at specified indexes in a string are returned by the charAt() method.

The first character has an index of 0, the second character has an index 1, etc.

Syntax

public char charAt(int index)

Parameters

The index of the character to return is an int value.

The following program shows the index number of the letter J:

Java String Method codePointAt()

A string containing the character at the specified index will be returned with the Unicode value using the codePointAt() method.

The first character has an index of 0, the second character has an index 1, etc.

Syntax

public int codePointAt(int index)

Parameters

index is an integer that takes the index number.

The following programme shows the Ascii code of the variable (e) as:

Here the given programme shows the Ascii Code of any alphabet as per user’s input:

Java String Method codePointBefore()

Using the codePointBefore() method, you can retrieve the Unicode value of the character before the specified index.

Initially, the first character is indexed as 0, then the second character is indexed as 1, and so on.

Parameters

A value of type int representing the Unicode index is displayed.

The following code shows the Ascii code of (M) which is 77:

The following example shows the multiple working of method codePointBefore() :

Java String Method codePointCount()

An array of Unicode values is counted using the codePointCount() method.

If you want to specify where to start the search and where to end it, you can use the startIndex and endIndex parameters.

As for the first character, its index is 0, then 1, then 2, etc.

Syntax

public int codePointCount(int startIndex, int endIndex)

Parameters

The startIndex is an integer value indicating where the string starts, the endIndex is an integer value indicating where the string ends.

The following example shows the unicodes of alphabets up to a range:

Java String Method compareTo()

Comparing two strings alphabetically is the purpose of the compareTo() method.

Each character in the string is compared based on its Unicode value.

If the string equals the other string, the method returns 0.

If the string is shorter than the other string (fewer characters), a value less than 0 is returned; if the string is longer than the other string, a value greater than 0 is returned.

Syntax

public int compareTo(String mrx_string)
public int compareTo(Object object)

Parameters

String 2 represents the other string that needs to be compared with a text string

Object shows objects to be compared are represented by objects

The following programme shows the comparison of two strings:

Correspondingly, we can also compare two user given strings in the way given below:

Java String Method compareToIgnoreCase()

Using the compareToIgnoreCase() method, two strings can be compared lexicographically without taking lowercase or uppercase into account.

Characters in the string are compared using their Unicode values converted into lower case.

0 is returned if the strings are equal, regardless of case differences. If the string is shorter than another string (fewer characters), it is returned as a number less than 0, and if it is longer than another string, it is returned as a number greater than 0.

Syntax

public int compareToIgnoreCase(String my_string)

Parameters

my_string is used as a search string ignoring the case it string contains.

The given programme takes two strings as user input and tells if they are equal or not irrespective of their case using the compareToIgnoreCase() method:

Java String Method concat()

A string can be attached to another string using the concat() method.

Syntax

public String concat(String mrx_string)

Parameters

Here, mrx_string shows the string to be appended/joined with another string.

The following programme shows the concatenation of the strings mrx and ample :

The following programme shows the joining of two strings:

Java String Method contains()

A string contains() method checks whether a sequence of characters exists in a string or not.

If the characters exist, then true is returned, otherwise false is returned.

Syntax

public boolean contains(CharSequence mrx)

Parameters

CharSequence mrx searches for the characters in the string.

An interface named CharSequence is an interface that allows a readable sequence of char values, which is part of the java.lang package.
The given example shows the working of the contains() method:

Similarly, we can also check if a user input contains a specific sequence of characters:

Java String Method contentEquals()

By calling contentEquals(), one can check if the contents of a string match those of a string or a string buffer.

The function returns true if the characters exist, and false otherwise.

Syntax

In the contentEquals() method, there are two methods available:

public boolean contentEquals(StringBuffer mrx)
public boolean contentEquals(CharSequence ample)

Parameters

StringBuffer mrx is the string to be searched for.
CharSequence ample contains a sequence of characters to be searched for in ample.

Java.lang contains the StringBuffer class, which is similar to the String class but allows modification.

Java.lang has an interface called CharSequence, which represents a sequence of char values.

The given programme shows the working of contentEquals() method:

The following programme performs the same operation by using contentEquals() method to search an exact block of characters using user’s input:

Java String Method copyValueOf()

Using the copyValueOf() method, you can obtain the characters of a char array as a String.

As a result, this method returns a new String array containing the characters copied from the previous array.

Syntax

public static String copyValueOf(char[] mrx, int ample, int count_mrx)

Parameters

The mrx consists of a character array.

The ample is an int value that represents the char array’s start index.

A count_mrx value represents the length of a character array as an int.

The given examples illustrates the copying of characters of a char array to a String:

We can also copy all characters from a char array by just using the char array name in the copyValueOf() method:

Java String Method endsWith()

Using the endsWith() method, you can check whether a string ends with a specific character(s).

Syntax

public boolean endsWith(String mrx)

In this case, mrx represents a String that contains the character(s) to be checked for.

The following programme shows the analyzation of string whether it ends with a specific sequence or not:

The following programme takes string as a user input and tells if it ends with a sequence of characters:

Java String Method startsWith()

Using startsWith(), you can check whether a string begins with the specified character or characters.

Syntax

public boolean startsWith(String mrx)

Parameters

In this case, the mrx is simply a string containing the character(s) you want to check for.

The given examples checks whether the given String starts with different sequences of characters:

Similarly, the following programme take one string as a user input and stores it, then takes another string input for the characters to be searched in the following string and returns the output as true or false:

Java String Method equals()

In the equals() method, two strings are compared to see if they are the same and the output is returned as true. If they are not the same, then false is returned.

Syntax

public boolean equals(Object mrx_String)

Parameters

Here mrx_String represents the second string to be compared with the first.

Correspondingly, the following programme takes two different strings as user input and shows if they are equal or not:

Java String Method equalsIgnoreCase()

By using equalsIgnoreCase(), you can compare two strings regardless of whether they are lowercase or uppercase.

A true value is returned if the strings are equal, whereas a false value is returned if they are not.

Syntax

public boolean equalsIgnoreCase(String mrx_String)

Parameters

mrx_String is another string to be compared with the first string, regardless of the case it has.

The following example explains the working of the equalsIgnoreCase() method:

The programme given below takes two strings as user input and compares them alphabetically ignoring the case they are written in:

Java String Method hashCode()

Using the hashCode() method, you can obtain the string’s hashcode.

Here’s how the hash code of a String object is calculated:

s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]

In this case, s[i] stands for a string’s ith character, n stands for its length, and ^ indicates exponentiation.

Syntax

public int hashCode()

Parameters

An integer value is returned as an output.

The following examples shows the hashcode of the string “Mr.Examples” :

The following programme shows the calculation of Hashcode after taking input from user:

Java String Method isEmpty()

The isEmpty() method checks the existence of an empty string in a string property.

According to this method, if the string is empty (length() is zero), it returns true, if not, then it returns false.

Syntax

public boolean isEmpty()

The working of isEmpty() method can be explained by following the example below:

Similarly, we can also check the isEmpty() method to check multiple Strings and user-defined string as well:

Java String Method indexOf()

Using indexOf(), you can find where the first occurrence of the specified character(s) is within a string.

Advice: To find the last occurrence of a specified character(s) in a string, use the lastIndexOf() method.

Syntax

IndexOf() has four methods:

public int lastIndexOf(String mrx)
public int lastIndexOf(String mrx, int ample_start_index)
public int lastIndexOf(int ample)
public int lastIndexOf(int ample, int mrx_start_index)

Parameters

The mrx parameter represents the string to search for.

ample_start_search and mrx_start_search are both integer data types that represent the position in the index from where it can begin the search. In the absence of this parameter, the length of the string is used instead.

An ample represents a single character, such as ‘A’ or a Unicode value.

Here, we find the index of the word about :

Here is an example of how the same work can be done by taking an input from the user:

The example below shows the Last Index of character d, while starting search from index number 2 :

Java String Method lastIndexOf()

Using the lastIndexOf() method, you can find out where a given character(s) appeared last in a string.

Syntax

The following four methods are available for lastIndexOf():

public int lastIndexOf(String mrx)
public int lastIndexOf(String mrx, int ample_start_index)
public int lastIndexOf(int ample)
public int lastIndexOf(int ample, int mrx_start_index)

Parameters

The mrx parameter represents the string to search for.

ample_start_search and mrx_start_search are both integer data types that represent the position in the index from where it can begin the search. In the absence of this parameter, the length of the string is used instead.

An ample represents a single character, such as ‘A’ or a Unicode value.

Here, we find the last index of the word about :

The same work could be done by taking an input from user, as shown below:

The example below shows the Last Index of character e, while starting search from index number 7 :

Java String Method length()

Using the length() method, you can get the length of any string.

Syntax

public int length()

The following example shows the length of a string containing numbers from 0 to 9:

We can also use user input to find the length of a string as shown below:

Java String Method replace()

Using replace(), you can replace a string with a new string containing the specified character(s) of the first string.

Syntax

public String replace(char mrx_search, char ample_new)

Parameters

mrx_search is a char that represents the character that is meant to replace the character that is currently in use.

An ample_new value is specified as a char, indicating the character that will be used to replace the mrx_search.

In order to better understand the String replace() method, have a look at the example below:

The following programme take inputs from user and replace the specified characters and displays the output accordingly:

Java String Method toLowerCase()

Using the toLowerCase() method, one can convert a string from upper case letters to lower case letters.

Important: Strings are converted to upper case letters by the toUpperCase() method.

Syntax

public String toLowerCase()

The given example will guide you regarding the working of toLowerCase() method:

Correspondingly, we can do the same operation on string after taking input from the user. THe given example demonstrates the working :

Java String Method toUpperCase()

By calling toUpperCase(), you can convert a string into uppercase letters.

Note : By using the toLowerCase() method, we can convert a string to lowercase characters.

Syntax

public String toUpperCase()

The example given below shows the conversion of a String of lowercase letters to Uppercase letters:

Accordingly, after receiving the user’s input, we can perform the same operation on the string. The following example illustrates how it works:

Java String Method trim()

In the trim() method, whitespace is removed from both ends of a string.

Syntax

public String trim()

Here is an example of how to remove whitespace from both sides of a string:

Correspondingly, here’s another example to demonstrate the working of trim() method in a easier way:

Java How To Count Words

Count Number of Words in a String

The following example can be used to easily count the number of words contained in a string:

Correspondingly, if you want to find the count of words in a user entered string, you can refer to the example below:

Java How To Reverse a String

You can easily revert a string’ s characters one by one by following the steps below:

Similarly, by taking an input from user we can also print the string in the reverted manner as shown in the example below: