Java String

Summary: in this tutorial, you will learn about Java String and how to manipulate strings effectively.

Introduction to Java String #

In Java, a string is a sequence of characters. Unlike primitive data types like int, char, and float, Java strings are objects. Java uses the String class to create and manipulate strings.

Declare a string #

To declare a string variable, you use the String class. For example:

String message;Copy

After having the string variable, you can assign a string literal to it. To construct a string literal, you place the text inside double quotes like this:

message = "Hello";Copy

Like other variables, you can declare a String variable and initialize its values at the same time:

String message = "Hello";Copy

Getting the length of a string #

To get the total of characters of a string, you use the length() method as follows:

str.length()Copy

where str is a String.

For example, the following displays the length of the string message with the value "Hello":

public class App {
    public static void main(String[] args) {
        String message = "Hello";
        System.out.println(message.length());
    }
}Copy

Output:

5Copy

Concatenate two strings #

To concatenate two strings into a single string, you use the + operator. For example:

public class App {
    public static void main(String[] args) {
        String greeting = "Hello " + "John";
        System.out.println(greeting);
    }
}Copy

In this example, we concatenate the strings "Hello " and "John" into a single string, assign it to the message variable, and output it to the screen.

Output:

Hello JohnCopy

Java also allows you to use += operator to append a string into another string. For example:

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

Output:

Hello JohnCopy

Accessing individual characters #

To access individual characters in a string, you can use the charAt() method.

Java String uses zero-based indexing. It means that the first character has an index of 0, the second character has an index of 1, and so on.

The following example shows how to get the first and last character of the String "Hello":

public class App {
    public static void main(String[] args) {
        String message = "Hello";

        char firstCharacter = message.charAt(0);
        char lastCharacter = message.charAt(message.length()-1);

        System.out.println(firstCharacter);
        System.out.println(lastCharacter);

    }
}Copy

Output:

H
oCopy

In this example, we get the first character by passing the index 0 and the last character by passing the index length - 1 to the charAt() method.

Comparing two strings #

To compare two strings, you don’t use the == operator. Instead, you use the equals() method:

s1.equals(s2);Copy

The equals() method returns true if s1 is equal to s2, or false otherwise.

public class App {
    public static void main(String[] args) {
        String s1 = "Hello";
        String s2 = "Hello";
        boolean isEqual = s1.equals(s2);

        System.out.println(isEqual); // true
    }
}Copy

Output:

trueCopy

Escape sequences #

An escape sequence represents a character that is difficult to include directly in a string. For example, newline, tab, backslash, etc.

An escape sequence starts with a backslash (\) followed by a character or a sequence of characters.

Here are the common escape sequences in Java:

When the Java compiler encounters escape sequences in a string, it interprets them accordingly. For example, if you want to place quotes in a string, you must use the escape sequence \":

public class App {
    public static void main(String[] args) {
        String message = "\"Java is awesome\".They said.";
        System.out.println(message);
    }
}Copy

Output:

"Java is awesome".They said.Copy

Java Strings are immutable #

In Java, strings are immutable. It means that once you create a string, you cannot change its content. For example:

String message = "Hi ";
message += "There.";

System.out.println(message); // Hi There.Copy

Output:

Hi There.Copy

The concatenation seems to change the string message.

But Java doesn’t modify the original string. Instead, it creates a new string with the value "Hi There." and assigns the string to the message variable.

Summary #

• Use the Java String class to declare a string variable.
• Use double quote (") to construct string literals.
• Java strings are immutable.
• Use the operator + to concatenate two strings into a single string.
• Use length() method to get the length of a string.
• Use equals() method to compare two strings.
• Use charAt() method to access individual characters in a string.