What are Strings in Java?
For producing and modifying strings in Java, there is a class called String. Among the classes that implement this interface is the String class. As a result, a string is essentially an object that holds a string of character values. To handle various string operations, we have multiple String methods like concat(), length(), compareTo(), equals(), etc. A string in Java is a collection of characters that is an object of the java.lang class. Learn more about object class methods in Java. A string’s value cannot be altered once it has been formed.
What is String in Java?
In Java, character-type variables are declared using the primitive data type char. It holds or represents a single character. Explore the top reasons why Java is still trending. However, what would happen if we had to save a name or a string of characters? There are two possible approaches (or techniques) to this:
Using char[] array in Java
public class Main
{
public static void main(String args[])
{
char[] ch = { ‘s’, ‘l’, ‘a’, ‘j’, ‘o’, ‘b’, ‘s’ };
System.out.println(ch);
}
}
Output
slajobs
Using string class in Java
public class Main
{
public static void main(String args[])
{
String stdName = “slajobs”;
System.out.println(stdName);
}
}
Output
slajobs
How to Create a String Object?
There are two methods for creating a string object:
Using String Literal
In computer science, a literal is a notation that is used to express a value. Double quotes can be used to produce and represent Java string literals. You can insert any character or anything between the two quotations.
Example
public class Main
{
public static void main(String args[])
{
String sJ= “SLA Jobs”; }
}
We have defined a string variable named sJ and initialized it with the string value “SLA Jobs” in the example above.
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String Constant Pool
String literals are kept in a storage space called the string constant pool in Java’s heap memory. The JVM verifies if the identical value already exists in the string pool before creating a new string. The reference to the already-existing object is returned if it does. If not, the reference to the newly formed string object is returned when it has been added to the string pool.
String str1 = “Soft”;
String str2 = “SLA”;
In the previous example, two strings are formed using the string literal function; why is only one string object created in the string constant pool?
The JVM searches the string constant pool for the string value “Soft” when str1 is initialized. If it is absent, a fresh string object is generated and kept within the pool.
The JVM looks for the string value “SLA” in the string constant pool when str2 is initialized. There is no need to construct a new string value because it already exists (because of str1). Rather, str2 references the current value.
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Using New Keyword
The new Java keyword can be used to construct strings, yes. A new instance of the String class is produced outside of the string constant pool in the heap memory when a string is formed using new. These objects are given their own memory space on the heap, unlike string literals, regardless of whether the identical value already exists there or not.
Syntax
String stringName = new String(“string_value”);
Example
String str = new String(“Welcome”);
System.out.println(str);
Example of Strings in Java
String val1 = “SLA “;
System.out.println(val1);
String val2 = new String(“Welcomes”);
System.out.println(val2);
String val3 = val1 + val2;
System.out.println(val3);
Output
SLA Welcomes
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Methods of Java String
int length() method
To find the length of a string in Java, use the length() function. Programs can behave differently depending on how long the string is, therefore this technique is particularly helpful in those situations.
Syntax
stringName.length()
Example
String genre = “hello”;
int genreLength = genre.length();
System.out.println(genreLength);
Output: 5
char charAt(int Index) method
The Java string charAt() method returns the character at the specified index number after receiving an index number as an input.
The string’s length, length, is the indexing range from 0 to length-1.
‘StringIndexOutOfBoundsException’ is produced if the passed index number is not present in the string (If it is a negative integer or equal to or larger than the string’s length).
Syntax
stringName.charAt(index)
Example
String str = “SLA Jobs”;
char ch = str.charAt(3);
System.out.println(ch);
Output: A
Exception Example
public class Main
{
public static void main(String args[])
{
String str = “slajobs welcomes you”;
char ch = str.charAt(21);
System.out.println(ch);
}
}
Output
Exception: java.lang.StringIndexOutOfBoundsException: String index out of range: 14
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String concat(String string1) Method
Two strings can be joined together using Java’s concat() function for strings.
Syntax
string.concat(anotherString)
Example
String str1 = “SLA”;
str1 = str1.concat(” Jobs”);
System.out.println(str1);
Output
SLA Jobs
String substring(int beginIndex, int endIndex[optional]) method
Java’s substring() function yields a specific portion of a string. The beginning index (inclusive) and the ending index (exclusive) are the two parameters required. The characters in the substring will go from beginIndex to endIndex – 1. It is considered that the endIndex is the string’s length if we do not supply it.
Syntax: string.substring(startIdx, endIdx)
Example
String str = “SLA Jobs”;
String str1 = str.substring(0, 6);
String str2 = str.substring(3);
System.out.println(str1);
System.out.println(str2);
Output
SLA Jo
Jobs
String equals(String anotherString) method
To determine whether two strings are equal or not, utilise Java’s equals() function. The equals method takes another string as a parameter and then determines whether the two strings are equal. True is returned if both strings are equal; otherwise, false is returned.
Syntax
string.equals(anotherString)
Example
String str = “sla”;
String str1 = “sla”;
String str2 = “sLA”;
String str3 = “welcomes”;
System.out.println(str.equals(str1));
System.out.println(str.equals(str2));
System.out.println(str.equals(str3));
Output
True
False
False
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String contains(String substring) Method
Java’s includes() function can be used to determine whether a string contains a given substring. If the substring is located, it returns true; if not, it returns false.
Syntax
string.contains(string)
Example
String str = “Welcome to SLA Jobs”;
System.out.println(str.contains(“Welcome”));
System.out.println(str.contains(“Hello”));
System.out.println(str.contains(“TO”));
Output
True
False
False
String Join()
As the name implies, the Java join() method for strings is used to join a collection of strings by creating a joiner between them. Any character, string, or combination of characters can be the joiner variable.
Syntax
string.join(joiner, str1, str2, str3,..)
Example
String strJoin = String.join(” “,”Hi”,”Hello”,”Welcome”,”to SLA”);
System.out.println(strJoin);
String str1Join = String.join(“-“,”Easy”,”way”,”to”,”IT Job”);
System.out.println(str1Join);
String str2Join = String.join(“/”,”20″,”12″,”2023″);
System.out.println(str2Join);
Output
Hi Hello Welcome to SLA
Easy-way-to-IT Job
20/12/2023
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int compareTo(String string1, String string2) Method
Java’s compareTo() function for strings compares the supplied strings according to their occurrence order in the dictionary. The Unicode value of each character in the strings is the only basis for comparison.
Syntax
string.compareTo(str1, str2)
Example
String str1 = “SLA Jobs”;
String str2 = “SLA Jobs”;
String str3 = “Jobs SLA”;
int result1 = str1.compareTo(str2);
System.out.println(result1);
int result2 = str1.compareTo(str3);
System.out.println(result2);
int result3 = str3.compareTo(str1);
System.out.println(result3);
Output
0
9
-9
String toUpperCase() Method
To convert a string’s lowercase characters to uppercase (or capital) characters in Java, use the toUpperCase() function.
Syntax
string.toUpperCase()
Example
String str = “get started”;
String strUpper = str.toUpperCase();
System.out.println(strUpper);
Output
GET STARTED
It should be mentioned that the original string str remains unchanged.
String toLowerCase() Method
To convert every character in a string to lowercase (or minuscule) characters in Java, use the toLowerCase() function.
Syntax
string.toLowerCase()
Example
String str = “Get Started”;
String strLower = str.toLowerCase();
System.out.println(strLower);
Output
get started
Example
String str = “KEYBOARD”;
str = str.toLowerCase();
System.out.println(str);
Output
get started
String trim() method
Java’s trim() function for strings is used to cut (or eliminate) unnecessary white spaces from both ends of the given string.
Syntax
string.trim()
Example
String str = ” Find Job at “;
System.out.println(str + ” SLA “);
str = str.trim();
System.out.println(str + ” SLA”);
Output
Find Job at SLA
Find Job at SLA
String replace(char oldChar, char newChar)
As the name indicates, the replace() function of the string in Java is used to replace every specified character in the string with a different character.
Syntax
string.replace(oldChar, newChar)
Example
String str = “Replace e with i”;
str = str.replace(‘e’,’i’);
System.out.println(str);
Output
Riplaci i with i
String Concatenation
In Java, string concatenation is the process of joining two strings together via the + operator or the concat() function. It’s crucial to remember that unless specifically changed, the original string stays unaltered.
Syntax
String resultantStr = str1 + str2 + …
Example
String str1 = “SLA “;
String str2 = ” Courses”;
String concatenated = str1 + str2;
System.out.println(concatenated);
Output
SLA Courses
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Creating Format Strings in Java
To format the string according to the provided argument, use the format() method. The formatted string is returned by this method, which first takes two arguments: the argument(s) and the format string.
Syntax
string.format(stringWithFormatSpecifier, anotherString)
Example
String str = “Computers”;
String str1 = String.format(“Domain: %s”, str);
System.out.println(str1);
Output
Domain: Computers
Escape Character() in Java Strings
The character that has a backslash \ preceding it is an escape character.
Example
public class Main
{
public static void main(String args[])
{
String escStr = “How to learn “coding” easily?”;
System.out.println(escStr);
}
}
Output
Main.java:4: error: ‘;’ expected
String escStr = “How to learn “coding” easily?”;
^
Main.java:4: error: ‘;’ expected
String escStr = “How to learn “coding” easily?”;
^
2 errors
Strings in Java: Mutable or Immutable
Because strings in Java are immutable, once they are initialized, they cannot have their values modified. This is because a single string object in the pool of string constants can have more than one reference. Conflicts may arise if the value of one reference is changed and it impacts other strings or reference variables. Java makes string objects immutable to avoid these problems. Java’s string immutability is strongly related to the idea of the String Constant Pool.
The actual string value is unchangeable, despite what some earlier sections of this article may have said.
Example
String str = “Dive Deep”;
System.out.println(str);
str = str + ” into Strings in Java”;
System.out.println(str);
Strings in Java are unchangeable. A new string value is produced when a string like “to all” is concatenated with str. Then, the old value is kept intact and str points to this newly produced value. This behavior illustrates Java’s string immutability.
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Conclusion
A fundamental element of both software development generally and the Java programming language is Java strings. Find out more by enrolling in Java training in Chennai at SLA Jobs.