Printing data

When you write programs, you often need to print calculation results, text, or any other type of data. Also, throughout this educational platform, you will write a lot of programs that print data on the screen. Let's learn how to do that using a standard approach in Java.

Displaying text using println() and print()

Standard output is a receiver to which a program can send information as text. It is supported by all common operating systems. Java provides a special System.out object to work with the standard output. We will often use it to print data.

The println method displays the passed string followed by a new line on the screen (print-line). For example, the following code snippet prints four lines.

System.out.println("I ");
System.out.println("know ");
System.out.println("Java ");
System.out.println("well.");

Here is the output we get:

I
know
Java
well.

All the strings were printed as they are, without double quotes.

This method allows you to print an empty line when no string is given:

System.out.println("Java is a popular programming language.");
System.out.println(); // prints empty line
System.out.println("It is used all over the world!");

And here is the output:

Java is a popular programming language.

It is used all over the world!

The print method displays the value that was passed in and places the cursor (the position where we display a value) after it. For example, the code below outputs all strings in a single line.

System.out.print("I ");
System.out.print("know ");
System.out.print("Java ");
System.out.print("well.");

We receive the following output:

I know Java well.

Pay attention to the spaces between words. We pass them to the method for printing.

New line using escape characters

In many programming languages, including Java, you can use an escape character \n which moves the cursor to the beginning of the next line of output. When you include \n in a string passed to System.out.print, it breaks the text at that point and continues printing on the following line. For example, the statement System.out.print("Hello\nWorld"); will output the following:

Hello
World

This option is useful when you need to break a long text into new lines in multiple places or when you need to have multiple new lines:

Hello



World

The following can be achieved by using three \n characters:

System.out.print("Hello\n\n\nWorld");

Printing numbers and characters

Both println and print methods allow a program to print not only strings and characters, but also numbers.

Let's print two secret codes.

System.out.print(108);   // printing a number
System.out.print('c');   // printing a character that represents a letter
System.out.print("Q");   // printing a string
System.out.println('3'); // printing a character that represents a digit

System.out.print(22);
System.out.print('E');
System.out.print(8);
System.out.println('1');

Here is our output:

108cQ3
22E81

As is the case with strings, none of the printed characters contain quotes.

Concatenating data

In practice, you may need to concatenate strings or other literals inside System.out.println into a single output. This can be achieved by simply placing them adjacent to each other and use the + operator to join them. For example, if you want to print a greeting with a name, you might write the following:

public class Main {
    public static void main(String[] args) {
        String name = "John";

        System.out.println("Hello, " + name + "!"); // Hello, John!
    }
}

The + operator merges these elements into one cohesive string, which is then passed to System.out.println to display the result on the console. Similarly, you can concatenate strings with integers or other types:

public class Main {
    public static void main(String[] args) {
        int age = 33;

        System.out.println("Hello, I am " + age + " years old."); // Hello, I am 33 years old.
    }
}

In such cases, the value of that type will be converted to a string and merged with the string to the left of the + operator.

Take in account that when you concatenate a string with multiple integers in Java, the integers are converted to their string representations and concatenated in sequence. Here’s how it works step-by-step:

public class Main {
    public static void main(String[] args) {
        System.out.println("Hello, I am " + 3 + 3 + " years old."); // Hello, I am 33 years old.
    }
}

You might expect the result to be "Hello, I am 6 years old" but when you concatenate the first integer with the string, you get "Hello, I am 3" as a result. The second + operator then merges this string with another 3, converting the integer to a string again.

Conclusion

In Java, you can print data via the standard output using the System.out object. You can use the println method to display the passed string in a print-line and the print method to output all passed strings in a single line. Both of these methods also allow for printing numbers as well as characters.