Java String Class

String is Java's class for text values, such as a person's name or a message. A String object keeps the same text after it is created. Methods can return another text value, but they do not edit the original String.

String name = "John";
String message = "Welcome to Java";

Here, "John" and "Welcome to Java" are strings.

Java provides the String class in the java.lang package to work with strings.

Because java.lang is automatically imported, we can use String without explicitly importing it.

String name = "John";

String is a Class in Java

Unlike primitive data types such as int, char, and boolean, String is a class.

String name = "John";

The variable name refers to a String object.

We can also explicitly create a String object:

String name = new String("John");

Both represent the text "John", but they differ in how the String object is created and how the String pool is involved.

Why is String Important in Java?

Strings are used almost everywhere in Java applications.

For example:

• User names
• Passwords and other text values
• Messages
• File paths
• URLs
• JSON data
• Database values
• Logs
• Search keywords

Example

String username = "john123";
String email = "john@example.com";
String city = "Bangalore";

Creating a String

The most common way is using a string literal:

String name = "John";

We can also create a String object using new:

String name = new String("John");

The difference between these approaches is explained in detail in the Ways to Create String in Java and String Pool in Java topics.

Strings are Immutable

One of the most important characteristics of Java's String class is that String objects are immutable.

Immutable means:

Once a String object is created, its contents cannot be changed.

Consider:

String name = "Java";
 
name = name + " Programming";

The original "Java" String object is not modified.

Instead, a new String object representing "Java Programming" is created, and name refers to that new object.

Example of String Immutability

String text = "Hello";
 
text.concat(" Java");
 
System.out.println(text);

Output

Hello

The concat() operation creates a new String, but the returned String was not assigned back to text.

To use the new value:

String text = "Hello";
 
text = text.concat(" Java");
 
System.out.println(text);

Output

Hello Java

String Class is final

The String class is declared as final.

Conceptually:

public final class String {
    // ...
}

Because it is final, another class cannot extend String.

class MyString extends String {
    // Error
}

This is one of the characteristics that contributes to the controlled behavior of String objects.

String and char

A char represents a single UTF-16 code unit:

char letter = 'A';

A String can contain multiple characters:

String word = "Java";

For example:

'A'       → char
"Java"    → String

Common String Operations

The String class provides many methods for working with text.

For example:

String text = "Hello Java";

Length:

text.length();

Convert to uppercase:

text.toUpperCase();

Check whether text is present:

text.contains("Java");

Extract part of a String:

text.substring(0, 5);

Compare strings:

text.equals("Hello Java");

These methods are covered in detail in the String Methods topic.

Comparing Strings

Do not use == when your intention is to compare String contents.

Use:

String a = "Java";
String b = "Java";
 
System.out.println(a.equals(b));

Output

true

The equals() method compares the contents of the strings.

== compares references rather than String contents.

String Example

public class HelloWorld {
 
    public static void main(String[] args) {
 
        String name = "John";
        String message = "Hello " + name;
 
        System.out.println(message);
        System.out.println(message.length());
        System.out.println(message.toUpperCase());
    }
}

Output

Hello John
10
HELLO JOHN

Key Characteristics of String

The Java String class has several important characteristics:

Key Takeaway

The String class in Java is used to represent and work with text. String objects are immutable, meaning their contents cannot be changed after creation. Java provides many built-in methods to compare, search, extract, and transform strings.