Java String methods

The String class includes various Java String methods for examining individual characters in a string. The String Methods perform various operations, including string comparison, search, copy, extracting a substring, converting to lowercase or uppercase, and so on.

A string is an immutable object that represents a sequence of characters. Once a string is created, it can’t be changed. However, there are many situations where we must perform different kinds of actions on a string. To do so, we must use the built-in Java string functions and assign the result set to a new string.

TIP: Please refer to the String article from Java to understand the creation of strings.

List of Java String methods

The following table shows the list of Java String Methods or functions available in the String Class. There is a separate article to explain each and every function, so use the hyperlinks to see the detailed explanation. However, this page gives a simple example for initial understanding.

Modifier Type	Java String Methods	Description
char	chartAt(int index)	It returns the Character at the specified index position
int	codePointAt(int index)	This returns the Unicode of the Character at a specified index position
int	codePointBefore(int index)	It returns the Unicode of the Character before the specified index position
int	codePointCount(int start_index, int end_index)	It returns the Unicode of the Character at the specified index position
int	comapreTo(String str)	It compares two strings lexicographically.
int	compareToIgnoreCase(String str)	It compares two strings lexicographically. While comparing, this method ignores the case difference.
String	concat(String str)	This method helps to join the user-specified string to the end of the string and return the new string.
boolean	contains(CharSequence s)	This returns TRUE if and only if the string contains the user-specified sequence of characters.
boolean	contentEquals(CharSequence s)	It compares the string with the user-specified sequence of characters
boolean	contentEquals(StringBuffer sb)	It compares the string with the user-specified StringBuffer
Static String	copyValueOf(char[] anCharArray)	Returns the string that represents the character sequence in the specified array.
Static String	copyValueOf(char[] anCharArray, int offset, int count)	Returns the string that represents the character sequence in the specified array, starting at offset until it reaches the specified count.
boolean	endsWith(String suffix)	It tests whether the string ends with the suffix that we specified or not
boolean	equals(Object anObject)	It compares this string with the user-specified object
Boolean	equalsIgnoreCase(String another_String)	It compares this string with the user-specified string (another_String). Note, while comparing, it ignores the case sensitivity.
static String	format (String format, Object.. args)	It will return a formatted string using the user-specified format and arguments.
static String	format (locale l, String format, Object.. args)	It returns a formatted string using the user-specified locale, format, and arguments.
byte[]	getBytes()	It converts the string into a sequence of bytes using the platform default charset and stores it in a byte array.
byte[]	getBytes(Charset charset)	It converts the given string into a sequence of bytes using the specified charset and stores it in a byte array.
byte[]	getBytes(String charset_Name)	This Java string functions convert the string into a sequence of bytes using the named charset and stores it in a byte array.
char[]	getChar()	It copies a character sequence from the given starting position to the end position.
int	hashCode()	It returns the Hash code of the Java string
int	indexOf(int ch)	It returns the index position of the first occurrence of a specified character. It returns -1 if the specified character is not found
int	indexOf(int ch, int Starting_Index)	It returns the index position of the first occurrence of a given character. It returns -1 if the specified character is not found
int	indexOf(String str)	It returns the index position of the first occurrence of a specified substring. It returns -1 if the specified string is not found
int	indexOf(String str, int Start_Index)	It returns the index position of the first occurrence of a specified substring. It returns -1 if the specified string is not found
String	intern()	Returns the canonical representation for the String Object
Boolean	isEmpty()	This function returns TRUE if the length of this string is zero
Boolean	isBlank()	Returns True if a string is empty or filled with blank spaces.
String	join()	Joins the group of words using a specified separator from an iterable, like an array.
int	lastIndexOf(int ch)	It returns the index position of the last occurrence of a specified character. It returns -1 if the given character is not found
int	lastIndexOf(int ch, int End_Index)	Returns the index position of the last occurrence of a specified character. It returns -1 if the specified character is not found
int	lastIndexOf(String str)	It returns the index position of the last occurrence of a given character. It returns -1 if the specified character is not found
int	lastIndexOf(String str, int End_Index)	Returns the index position of the last occurrence of a specified character. It returns -1 if the given character is not found
int	length()	This returns the length of this string
boolean	matches(String regexp)	It tells whether this string matches a user-specified regular expression or not.
int	offsetByCodePoints(int index, int codePointOffset)	It returns the index within the string that is offset of a given index by codePointOffset code points
boolean	regionMatches(int toffset, String other, int offset, int len)	It test if two string regions are equal or not
boolean	regionMatches(boolean ignorecase, int toffset, String other, int offset, int len)	It tests if two string regions are equal or not
String	replace(char Old_Character, char New_Character)	Searches for specified characters and then replaces all the occurrences of Old_Character with New_Character
String	replace(CharSequence Old_sequence, CharSequence New_sequence)	It searches for a specified substring and then replaces all the occurrences of the Old_sequence substring with the new New_sequence substring.
String	replaceAll(String regexp, String replacement)	This Method searches for a specified regular expression. Then replace all the occurrences of the regular expression substring with the given replacement substring.
String	replaceFirst(String regexp, String replacement)	It searches for a specified regular expression and then replaces the first occurrence of the regular expression substring with the given replacement substring.
String	repeat()	Repeats a string for a given number of times.
String[]	split(String regex)	It splits the string into an Array of Substrings based on the separator we specified
String[]	split(String regex, int limit)	This one splits the string into an Array of Substrings based on the separator we specified
boolean	startsWith(String prefix)	It tests whether the string starts with the prefix that we specified or not
boolean	startsWith(String prefix, int limit)	It tests whether the substring of this string starts with the prefix that we specified or not
CharSequence	subsequence(int Starting_Index, int End_Index)	Returns a new sequence that is after the given sequence.
String	substring(int Starting_Index)	It extracts the characters from a string based on the specified indices
String	substring(int Starting_Index, int End_Index)	It extracts characters from a string based on the specified starting and end positions.
String	strip()	Removes leading and trailing blank spaces from a given string.
String	stripLeading()	Removes leading white spaces from a given string.
String	stripTrailing()	It removes trailing blank spaces from a given string.
char[]	toCharArray()	This converts the given string into an Array of Characters or a character array
int	toLowerCase()	It converts the given string into Lowercase letters using the default locale
String	toLowerCase (Locale locale)	It converts the given string into Lowercase letters by considering the user-specified locale
string	toString()	This String Method converts the given value into a String Object
string	toUpperCase()	It converts the given string into Uppercase letters
string	toUpperCase (Locale locale)	It converts the given string into Uppercase letters by considering the host environment’s current locale
string	trim()	This removes the white spaces from both ends
static String	ValueOf(boolean number)	Returns the string representation of the Boolean value
static String	ValueOf(char character)	String representation of a char
static String	ValueOf(char[] myArray)	String representation of a character array
static String	ValueOf(char[] myArray, int Offset, int count)	This returns the string representation of a subset character array.
static String	ValueOf(double number)	String representation of a double value
static String	ValueOf(float number)	String representation of a float value
static String	ValueOf(int number)	It returns the string representation of the Integer value.
static String	ValueOf(long number)	It returns the string representation of the Long value.
static String	ValueOf(Object obj)	String representation of an Object.

Java String methods for case conversion

The toLowerCase() and toUpperCase() functions help convert the given string to lowercase and uppercase.

toLowerCase()

The toLowerCase() method does not accept any parameters and converts all characters in a given string to lowercase.

public class example {
	public static void main(String[] args) {	
		String s = "uNITED sTATES";
		System.out.println(s.toLowerCase());
	}
}

united states

toUpperCase()

Similar to the toLowerCase(), the toUpperCase method does not accept any parameters and converts a given string’s characters to uppercase.

public class example {
	public static void main(String[] args) {		
		String s = "united states";
		System.out.println(s.toUpperCase());
	}
}

UNITED STATES

Java string methods for comparison

There are two built-in string methods to perform string comparison: equals() and equalsIgnoreCase().

equals()

The equals() method accepts a string for comparison and checks whether the given two strings are equal or not. If they both are equal, it returns a Boolean True; otherwise, it returns false.

The following Java string methods example returns false because the equals() method is case-sensitive. So, both “USA” and “usa” are not the same.

public class example {
	public static void main(String[] args) {	
		String s1 = "USA";
		String s2 =  "usa";
		System.out.println(s1.equals(s2));
	}
}

false

equalsIgnoreCase()

Unlike the equals() method, the equalsIgnoreCase() function performs string comparison irrespective of case. It returns true if they are both equal; otherwise, it returns false.

TIP: For case-sensitive string comparison, use the equals() method. On the other hand, use the equalsIgnoreCase() function for case-insensitive comparison.

public class example {
	public static void main(String[] args) {	
		String s1 = "USA";
		String s2 =  "usa";
		System.out.println(s1.equalsIgnoreCase(s2));
	}
}

true

Java string functions – contentEquals()

The contentEquals() method also performs the string comparison. It checks whether both strings have the same character sequence.

public class example {
	public static void main(String[] args) {	
		String s1 = "UK";
		String s2 =  "UK";
		System.out.println(s1.contentEquals(s2));
	}
}

true

compareTo()

The compareTo() method is one of the Java string methods that compares the two strings lexographically. It converts the characters in both strings into Unicode values and compares them against each other. If they are equal, it returns 0; otherwise, the compareTo() returns either a positive or negative value based on the number of characters.

public class example {
	public static void main(String[] args) {	
		String s1 = "WHO";
		String s2 = "WHO";
		System.out.println(s1.compareTo(s2));
	}
}

NOTE: If you add another character (O) at the end of the first string, the result is 1. If we add to the second string, the result is -1.

Java string functions – compareToIgnoreCase()

Similar to the compareTo() method, the compareToIgnoreCase() function compares the two strings lexographically without considering cases. Remember, the compareTo() performs case-sensitive string comparison. On the other hand, the compareToIgnoreCase() function ignores cases when comparing two strings.

public class example {
	public static void main(String[] args) {	
		String s1 = "WHO";
		String s2 = "who";
		System.out.println(s1.compareToIgnoreCase(s2));
	}
}

regionMatches()

Instead of comparing the whole string, the regionMatches() function compares a region (or part) of one string against the part of another string.

In the following Java string functions example, the character at index position 7 is “S”. So, the regionMatches() function compares States against the States from the second string.

public class example {
	public static void main(String[] args) {	
		String s1 = "United States";
		String s2 = "States";
		System.out.println(s1.regionMatches(7, s2, 0, 6));
	}
}

true

Java String methods for search operations

The following string functions perform the search operations.

indexOf()

The indexOf() function searches for the specified substring and returns the index position of the first occurrence. If the substring is not found, the indexOf() returns -1.

Although the “united” substring is repeated twice in a given string, the indexOf() returns the first occurrence index position. So, the result is 4.

public class example {
	public static void main(String[] args) {	
		String s = "The united states and united kingdom";
		System.out.println(s.indexOf("united"));
	}
}

Java string methods – lastIndexOf()

The lastIndexOf() function searches for the last occurrence of a specified substring and returns the index position. If the substring is not found, the lastIndexOf() returns -1.

Although the “united” substring is available at index position 4, it returns 22 because the last occurrence is at that position.

public class example {
	public static void main(String[] args) {	
		String s = "The united states and united kingdom";
		System.out.println(s.lastIndexOf("united"));
	}
}

contains()

The contains() method accepts a substring and checks whether the specified sequence of characters exists in a given string. If it exists, the contains() function returns Boolean true; otherwise, it returns false.

public class example {
	public static void main(String[] args) {	
		String s = "The United Kingdom";
		System.out.println(s.contains("King"));
	}
}

true

NOTE: The contains() method is case sensitive; King and king are different.

Java string functions – startsWith()

The startsWith() function checks whether the string starts with a specified substring and returns true if it does; otherwise, false.

public class example {
	public static void main(String[] args) {	
		String s = "The United States";
		System.out.println(s.startsWith("Th"));
	}
}

true

endsWith()

The endsWith() function checks whether the specified string ends with a given substring and returns true if it does; otherwise, false.

public class example {
	public static void main(String[] args) {	
		String s = "The United States";
		System.out.println(s.endsWith("United"));
	}
}

false

Java String methods for string extraction

The string function that we mentioned here helps extract a single character, a substring, or a character sequence from a given string.

charAt()

The charAt() function accepts an integer value and returns the character at the given index position. The following example returns the character at the 12^th index position (13^th character).

public class example {
	public static void main(String[] args) {
		String str = "The Unites States Of America";
		char str1 = str.charAt(12);
		System.out.println(str1);
	}
}

Java string functions – codePointAt()

The codePointAt() function accepts the index position as an argument and returns the Unicode value of a character at that position. The following example returns the 101 because the character at the 8^th index position is “e” and its ASCII value is 101.

public class example {
	public static void main(String[] args) {
		String s = "The Unites States";
		System.out.println(s.codePointAt(8));
	}
}

codePointBefore()

The codePointBefore() function returns the Unicode value of a character before the specified index position. The following Java string functions example returns 85 because the character at the 4^th index position (before the specified position) is “U” and its ASCII value is 85.

public class example {
	public static void main(String[] args) {
		String s = "The Unites States";
		System.out.println(s.codePointBefore(5));
	}
}

substring(int startIndex, int endIndex)

The substring() function accepts the starting and ending index positions as argument values. Next, the substring() returns a portion of the main string between those index positions (start, end – 1).

public class example {
	public static void main(String[] args) {	
		String s = "united kingdom united states";
		System.out.println(s.substring(7, 21));
	}
}

kingdom united

Java string methods – subSequence()

Similar to the substring() function, the subSequence() method returns a new character sequence from the given starting and ending index positions.

public class example {
	public static void main(String[] args) {	
		String s = "United Arab Emirates United Kingdom";
		System.out.println(s.substring(12, 27));
	}
}

Emirates United

Java String functions to replace a string

There are two versions of the replace() function, and other methods help perform string replacement.

replace(char old, char new)

The replace() function accepts two characters as arguments and performs the character replacement. It searches for the old characters in a given string and replaces them with new characters.

public class example {
	public static void main(String[] args) {	
		String s = "united kingdom";
		System.out.println(s.replace("n", "T"));
	}
}

uTited kiTgdom

Java string functions – replace(substring, substring)

Apart from a single character, we can use the replace() function to replace a character sequence or substring with a completely new string.

public class example {
	public static void main(String[] args) {	
		String s = "The united states and united kingdom";
		System.out.println(s.replace("united", "UN"));
	}
}

The UN states and UN kingdom

replaceAll()

The replaceAll() function replaces all occurrences of character sequences with a new string. It uses the regular expression as the first argument to search for multiple characters. The example below replaces all occurrences of the “u” and “t” with the “#” special character.

public class example {
	public static void main(String[] args) {	
		String s = "united states and united kingdom";
		System.out.println(s.replaceAll("[ut]", "#"));
	}
}

#ni#ed s#a#es and #ni#ed kingdom

replaceFirst()

The replaceFirst() function is one of the Java string methods that replaces the first occurrences of a character sequence with a new string. No matter how many times the old character(s) are repeated, they replace the first occurrence.

public class example {
	public static void main(String[] args) {	
		String s = "united states";
		System.out.println(s.replaceFirst("[ut]", "#"));
	}
}

#nited states

Java String functions to remove blank spaces

The trim() method is the most commonly used one to remove blank spaces. However, Java 11 introduces three more built-in string functions to remove white spaces from leading, trailing, and both.

trim()

The trim() method removes the white spaces from both sides of a string. It removes leading and trailing blank spaces. The following example removes the blank spaces from the left and right sides of the ” The United Kingdom ” message.

public class example {
	public static void main(String[] args) {	
		String s = "     The United Kingdom    ";
		System.out.println(s.trim());
	}
}

The United Kingdom

strip(), stripLeading(), stripTrailing()

These three Java string methods were introduced in Java 11.

strip(): Similar to the trim() function, the strip() method removes blank spaces from the left and right sides of a given string.
stripLeading(): As the name suggests, it removes the leading blank spaces.
stripTrailing(): As the name suggests, it removes the trailing blank spaces.

The following example demonstrates the strip(), stripLeading(), and stripTrailing() functions.

public class example {
	public static void main(String[] args) {	
		String s = "     The United States    ";
		System.out.println(s.strip());
		System.out.println(s.stripLeading());
		System.out.println(s.stripTrailing());
	}
}

Result

The United States
The United States    
     The United States

Java String functions for concatenating Strings

Generally, users use the arithmetic + operator to perform string concatenation. However, we must use the built-in concat() function to join multiple strings.

concat()

As the name suggests, the concat() method performs string concatenation. It appends the given argument (substring) at the end of the specified string.

public class example {
	public static void main(String[] args) {	
		String s1 = "The United ";
		String s2 = "Arab Emirates";
		System.out.println(s1.concat(s2));
	}
}

The United Arab Emirates

Java string functions – join()

The join() method helps to join the elements from an iterable (for example, an array) to form a string. It uses the first argument to separate each word from the iterable.

In the following example, we join the words from a string array. Here, the join() method uses a comma and a space delimiter to separate each word.

public class example {
	public static void main(String[] args) {
		String[] countries = {"India", "USA", "UK", "China"};
		String s = String.join(", ", countries);
		System.out.println(s);
	}
}

India, USA, UK, China

Other Java string functions

codePointCount()

The codePointCount() function accepts the start and end index positions and counts the Unicode points between them.

public class example {
	public static void main(String[] args) {
		String s = "The Unites States";
		System.out.println(s.codePointCount(2, 6));
	}
}

hashCode()

The hashCode() method is one of the Java string functions that returns the hash code value of a given string. There is a mathematical formula behind the hashCode calculation that we discussed in the hashCode article.

public class example {
	public static void main(String[] args) {	
		String s = "Hi";
		System.out.println(s.hashCode());
	}
}

Java string methods – repeat()

The repeat() method repeats the given string for the given number of times. It accepts an integer value and repeats for this many times. The following example repeats “Hi ” three times.

public class example {
	public static void main(String[] args) {	
		String s = "Hi ";
		System.out.println(s.repeat(3));
	}
}

Hi Hi Hi

length()

As the name suggests, the length() function is one of the Java string functions that returns the length of a given string. In other words, it returns the total number of characters in a user-given string, including blank spaces.

The declared string in the following example has 13 characters and a blank space, so a total of 14 characters.

public class example {
	public static void main(String[] args) {		
		String s = "United Nations";
		System.out.println(s.length());
	}
}

offsetByCodePoints()

The offsetByCodePoints() function helps to move some Unicode points within a string. The example below moves two characters forward.

public class example {
	public static void main(String[] args) {	
		String s = "United";
		System.out.println(s.offsetByCodePoints(0, 2));
	}
}

Java string functions for split & format

split()

The split() method splits the given string into an array of substrings based on the specified separator. We can use a single character, a substring, or a regular expression as the separator. There is an optional second argument to limit the split process.

import java.util.Arrays;
public class example {
	public static void main(String[] args) {	
		String s = "INDIA, CHINA, USA, UK, FRANCE";
		String[] str = s.split(", ");
		System.out.println(Arrays.toString(str));
	}
}

[INDIA, CHINA, USA, UK, FRANCE]

NOTE: We can use the for loop to iterate over the string array items. For simplicity, we used the Array toString() function.

format()

The format() method helps format the user-given string using format specifiers. The following example is a simple demonstration of the Java string functions complex nature.

public class example {
	public static void main(String[] args) {	
		String s = "United States";
		String fs = String.format("The %s GDP is %.2f", s, 3.5);
		System.out.println(fs);
	}
}

The United States GDP is 3.50

Java String functions for conversion

copyValueof()

The copyValueOf() method returns the string representation of the sequence of characters specified in a character array.

public class example {
	public static void main(String[] args) {	
		char[] ch = {'I', 'n', 'd', 'i', 'a'};
		String s = String.copyValueOf(ch);
		System.out.println(s);
	}
}

India

getBytes()

The getBytes() method is one of the Java string functions that converts each character in a given string into an ASCII value and returns an array containing a sequence of bytes. We can use either a for loop or built-in array functions to read the array.

public class example {
	public static void main(String[] args) {	
		String s = "INDIA";
		
		byte[] bt = s.getBytes();
		System.out.println(Arrays.toString(bt));
	}
}

[73, 78, 68, 73, 65]

getChars()

The getChar() function accepts four arguments, which include the source starting and ending positions, the destination character array, and the starting position of the destination.

public class example {
	public static void main(String[] args) {	
		String s = "INDIA";
		int ln = s.length();
		
		char[] cs = new char[ln];
		s.getChars(0, ln, cs, 0);
		System.out.println(cs);
		for (char ch: cs) {
			System.out.format("%c ", ch);
		}
	}
}

Result

INDIA

I N D I A

TIP: If you change the first argument value from 0 to 2, the above returns “DIA”.

toCharArray()

The toCharArray() method is one of the java string functions that converts the given string into a character array. We can perform various operations at the character level in a Char array.

public class example {
	public static void main(String[] args) {	
		String s = "The united states";
		char[] cn = s.toCharArray();
		System.out.println(cn);
	}
}

The united states

Java string methods – toString()

The toString() function returns a string representation of a given object. We can use the toString() function to convert any data type to a string. In the following example, the integer value 1000 is converted into a string.

public class example {
	public static void main(String[] args) {		
		Integer n = 1000;
		System.out.println(n.toString());
	}
}

valueOf()

The valueOf() function converts different kinds of data types, such as integers, Boolean, etc., to a string.

public class example {
	public static void main(String[] args) {	
		boolean exists = true;
		System.out.println(String.valueOf(exists));
	}
}

true

TIP: The toString() method converts an object to a string. On the other hand, the valueOf() method converts a value to a string object.

intern()

The intern() method is one of the built-in Java string functions that returns the canonical representation of a given string. It is helpful in the string pool. The intern () method looks inside the string pool for the value, if it exists, references that subject; otherwise, it creates a new string with this text inside a string pool.

public class example {
	public static void main(String[] args) {	
		String s1 = "USA";
		String s2 = new String("USA");			
		System.out.println(s1 == s2);
		System.out.println(s1 == s2.intern());
	}
}

Result

false
true

Java String methods for validation

matches()

The matches() function checks whether the given string matches the user-specified regular expression or not. It returns True if it matches; otherwise, Boolean False. It’s a kind of wildcard matching.

The first statement returns false because both are not the same. However, in the second statement, we used (.*), which means it should start with United, followed by N number of characters (true).

public class example {
	public static void main(String[] args) {	
		String s = "United Arab Emirates";
		System.out.println(s.matches("United"));
		System.out.println(s.matches("United(.*)"));
	}
}

Result

false
true

isEmpty()

As the name suggests, the isEmpty() function checks whether the given string is empty or not. If it is empty, it returns Boolean True; otherwise, it returns False.

public class example {
	public static void main(String[] args) {	
		String s = "";
		System.out.println(s.isEmpty());
	}
}

true

Java string methods – isBlank()

Similar to the isEmpty() function, the isBlank() method checks whether the given string is empty or not. However, it checks for an empty string and a string with empty spaces. If it is empty or filled with empty spaces, it returns Boolean True; otherwise, it returns False.

public class example {
	public static void main(String[] args) {	
		String s = " ";
		System.out.println(s.isBlank());
	}
}

true