1.1 Printing and Comments

Printing

Through our first program, we were exposed to a command that outputs information to the screen:

System.out.println("Hello");

It's a simple command, but there is a lot happening. Here is a breakdown of the command:

• System.out - a java library containing tools for outputting
• println() - a command to specifically output the contents followed by a carriage return
• "Hello" - the value to be outputted, known as a string. String values are enclosed within " "
• ; - statements end with a semicolon

You Try

System.out.println("Hi");
System.out.println("There!!");

Printing without a new line

Try this:

System.out.print("Hi");
System.out.print("There!!");

Similar to println(), print() outputs to the screen, however, there is no newline placed after the what is outputted.

Concatenation (Joining Text Together)

In Java, we can combine strings together using the + operator. This is known as concatenation. It's useful when you want to build up output from multiple pieces of text or variables:

System.out.println("Hello " + "World!");

This will output:

Hello World!

We can also concatenate text with variable values:

String name = "Mr. Cheng";
System.out.println("Hello, " + name);

This will output:

Hello, Mr. Cheng

Comments

In our programs, we often have content that we want the compiler to ignore and not translate. Some reasons are:

• descriptions of the overall program
• multi-line descriptions of parts of the code
• single line descriptions of commands
• ignoring code for troubleshooting

Single Line Comments //

In Java, we can ignore single lines of code by putting a // infront of it.

Multiline Comments /* */

If we want to have comment span multiple lines, we use /* */

// Draw a box
System.out.println("*************");
System.out.println("*           *");
System.out.println("*           *");
System.out.println("*           *");
System.out.println("*************");
      
// Draw another box
/*
System.out.println("*************");
System.out.println("*           *");
System.out.println("*           *");
System.out.println("*           *");
System.out.println("*************");
*/