Working with Strings

In this section, you will learn the basics of strings.

A string is a sequence of characters. String literals are enclosed in double quotes (").

Here’s an example of a string.

"Hello, world!"

In Java, string is not a primitive type. It is a reference type. It is implemented by the String class.

Even though String is a reference type, it is treated specially. We take an entire chapter to explain strings. Here, we teach you the basics. It will help you understand upcoming examples.

Declaring Strings

Strings are declared like any reference type. Here’s an example.

String title;

Here, we declared a variable named title. It can store a reference to a String object.

Initializing Strings

Unlike other reference type variables, strings are initialized like primitive types.

Remember String isn’t a keyword. It’s a class defined by the Java API.

Here’s an example of initializing a String variable.

String message;
message = "How are you?";

Here, we declared a variable named message of type String. We initialized it to "How are you?". Remember that string literals are enclosed in double quotes ("), not in single quotes. Single quotes are used for character literals.

You can combine declaration and initialization like this.

String message = "How are you?";

To initialize a local string variable to an empty string, use a statement like this.

String string = "";

You know that Java is case sensitive. Which means, String with uppercase S and string with lowercase are different.

Joining Strings

You can join two strings by using the concatenation operator (+). Concatenation means joining two strings.

Here’s an example where two strings are joined.

public class JoiningStrings {

    public static void main(String[] arguments) {
        String hello = "Hello, ";
        String world = "world!";
        String message = hello + world;

        System.out.println(message);
    }
}

When you join strings, no extra characters are added by Java. This includes any blank spaces between strings. If you want to combine two strings with a space in between them, you’ve to do it. In the previous example, the first string ends with a space.

Here’s another example where two strings are joined with and without space in between them.

public class JoiningStringsWithSpace {

    public static void main(String[] arguments) {
        String hello = "Hello,";
        String world = "world!";
        String message1 = hello + " " + world;
        String message2 = hello + world;

        System.out.println(message1);
        System.out.println(message2);
    }
}

You can join a string with any primitive type, such as int and float. Java converts the primitive value to a string and then joins it.

Here’s an example where a string is joined with a boolean value.

public class JoiningStringsWithPrimitiveValues {

    public static void main(String[] arguments) {
        String question = "Are you Batman?";
        boolean answer = true;
        String message = question + " " + answer;
        System.out.println(message);
    }
}

Here we declared a String variable named question. It holds a simple question. We declared boolean variable named answer. It holds true. We joined question and answer using the concatenation operator (+). The result was stored in message. We have added a blank space to seperate the question and answer. Finally, we printed the string stored in message.

Converting Strings to Primitives

You can convert a string into a primitive value. For example, you can convert the string "27" written with digits into a primitive value. But you can’t convert the string “twenty seven”` written in words into an integer.

You can use one of the following methods to convert a string to a primitive value.

You will learn more about methods later in the book.

Wrapper Class Method
Boolean parseBoolean
Character –
Byte parseByte
Short parseShort
Integer parseInt
Long parseLong
Float parseFloat
Double parseDouble

Here’s an example of converting strings to primitive values.

boolean value1 = Boolean.parseBoolean("true");
byte value2 = Byte.parseByte("27");
short value = Short.parseByte("519");
int value = Integer.parseInt("2000");
long value = Long.parseLong("1999");
float value = Float.parseFloat("5.19");
double value = Double.parseDouble("9.21");