Printlns

Note

Above, you’ll see there’s a video titled For CSE 121: Printlns Video Walkthrough. The video and the reading both have the same information! You’re not required to go through both the video and the reading, as the video just walks through the reading to help contextualize it!

Imagine you’re writing an essay in a text editor, like Google Docs, but you don’t have access to the arrow keys or the mouse. You can type any text, but you can’t move around the document or freely type anywhere you want!

This idea of typing without arrow keys or a mouse is how Java behaves when we print (i.e. display) text to the screen.

There are two such methods (i.e. commands) that we use to display content to the screen. Namely, they are:

• System.out.print

• System.out.println

Note

The only thing that’s different between the two methods is the extra ln in System.out.println

System.out.println ✏️

The System.out.println method “prints” some text to the screen and moves to a new line. (This second part is very important!) We refer to this “move to a new line” as a new-line character.

Tip

Tip It might help to remember this by reading println as “print line”

What does this mean and how do we use this method? Suppose we wanted to display the text “Welcome to CSE 121!” on the screen, we would do so with the following statement:

System.out.println("Welcome to CSE 121!"); 

Let’s see this in the context of a full Java program. Press the “Run” button on the code block below to run the program and see the output.

public class Welcome {
    public static void main(String[] args) {
        System.out.println("Welcome to CSE 121!");
    }
}

Warning

Watch out! Don’t forget the double quotes inside the println statement! We always need quotes when we’re printing out text, otherwise your program won’t run 😢 More on why the quotes are necessary soon!

The text inside the quotes can be anything! Try changing the text inside the System.out.println method above to say “Hello, world!” instead of “Welcome to CSE 121!”. The expand snippet below has a possible solution for this!

public class Welcome {
    public static void main(String[] args) {
        System.out.println("Hello, world!");
    }
}

We can stack multiple System.out.println methods, to display multiple sentences to the console. Try running the following program and examine its output.

public class Welcome {
    public static void main(String[] args) {
        System.out.println("Welcome to CSE 121!");
        System.out.println("Hope you have a great time");
    }
}

Using println statements makes the output prints on two separate lines! Let’s break this down:

Remember that

• The System.out.println method “prints” some text to the screen and moves to a new line

• So, if we look at the first time we’re using the System.out.println method (on line 3), we display the text “Welcome to CSE 121!” and move our cursor to the next line

• We then display the text “Hope you have a great time” starting on the next line!

Looking at this example, we can see that the println method acts like typing text to the screen and then hitting the enter (or return) key on your keyboard!

System.out.print

The System.out.print method also “prints” some text to the screen. This feels just like the System.out.println method… 🤔 What’s different? Sometimes, you want to have finer-grained control of how your printing is formatted. print operates just like println but does not include a new-line at the end. Let’s see this in practice:

public class Welcome {
    public static void main(String[] args) {
        System.out.print("Welcome to CSE 121!");
    }
}

Try running the program above. Now, scroll back up to where we printed the same message using the println statement. Why aren’t there any differences in the output between the print and the println method? Shouldn’t the println command move to the next line… Well it did! We just can’t see it on our screen, because we haven’t printed anything new on that next line 😦

Maybe we’ll notice the difference if we display two sentences on the screen using the print command. Let’s use the same sentences that we tried previously with our println command. Run the code block below to see what happens.

public class Welcome {
    public static void main(String[] args) {
        System.out.print("Welcome to CSE 121!");
        System.out.print("Hope you have a great time");
    }
}

So what’s happening here? Why do these sentences display on the same line? Let’s break this down:

• Remember that > The System.out.print method “prints” some text to the screen, but does not include a new-line at the end

• So, if we look at the first time we’re using the System.out.print method (on line 3), we print the text “Welcome to CSE 121!” and stay on the same line

• We then print the text “Hope you have a great time” starting at the same place we ended our last sentence, and again stay on the same line!

This method behaves exactly like how text editors do! You type a sentence, and you don’t automatically to a new line; you start typing the next sentence exactly where you left off with your previous sentence.

Notice that there are no spaces after each thing printed, since print doesn’t include any trailing characters. If you would want the program to have spaces between calls of print, you must include the spaces yourself in the text you are printing.

Mixing print and println ✏️

It is completely possible to mix your use of both print and println to format your output how you want! This will make more sense when later in the course, but for example you could write a program like the following. Note that each call to print prints the text exactly while each call to println prints the text and then moves to the next line.

public class Printing {
    public static void main(String[] args) {
        System.out.print("A");
        System.out.print("A");
        System.out.println("A");
        System.out.print("B");
        System.out.println("B");
        System.out.println("C");
    }
}

Main Points:

System.out.println is a command that prints out the specified text, and then moves to a new line. System.out.print is a command that prints out the specified text without moving to a new line.