Simple output

In the Hello program you used the line System.out.println("Hello") to write `Hello' to the screen. This is the standard way of outputting to the screen and it works for numbers and variables (see previous section) as well. If you want to print several things at the same time you can use the + symbol as follows.

System.out.println("Hello" + 1.234);
System.out.println("Hello " + "number " + 1.234);
System.out.println("The value of variable x is: " + x);

The first two commands result in the outputs `Hello1.234' and `Hello number 1.234' respectively. The third command will print to the screen `The value of variable x is: ' followed by whatever number, character, or string, is stored in the x.

You can add separate Strings together using +, e.g. String name = "Bob" + " Smith". Or String id = "abc" + 1.4 creates a string called id which stores `abc1.4'. Here 1.4 is a number but it is automatically converted into a string before being added to "abc". We explore strings a little more in the next section, which is on output, where you will see that it is equally possible to have instead of a number, a variable, where the value of the variable is added to the string in the same way that the number is above.

Exercise 1.4

(4 marks)

Try programming output yourself.

• Make a copy⁵ of your program VarTry.java, call it VarTry2.java, and change the class name to match the new file name.

• Alter VarTry2 so that you also declare a double variable, x, assign it a value and print this to the screen.

• Compile and run your program to check the output is what you expect.

• Next modify your program to create a string and print that to the screen as well. Compile and run your program to check the output is what you expect.

• Finally modify your program again to declare a second double variable y, assign it a value, and add the statement System.out.println(x + y); to your code. Again, compile and run your program to check the output is what you expect.

• Write in your lab notebook what the program outputs to the screen.

• Alter your program to System.out.println(x + " " + y) to see the two values printed to your screen separately.

• Your program listing, sample output and your answer to all these questions should all go in your lab notebook.

If you wish to print several things to the screen on the same line without using + all the time, you can use System.out.print() which works in the same way as the System.out.println() you've just been using, but will not move to the next line each time.