Tutorials : Making the Switch to Java :

Part 2 - Getting User Input

Welcome to the second of my Java tutorials. In this tutorial I am going to go over how to obtain the user's input. As you may realise this is quite an important topic as if you didn't know how to do this, your programs would be very boring!

Fire up your text editor of choice and enter the following program:

import java.io.*;

public class UserInput {

public static void main(String [] args) throws IOException {

BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
String name = "";

System.out.println("Enter your name: ");
System.out.flush();
name = in.readLine();
System.out.println("Thank you. " + name);

}

}

This code looks more like it! Now remember to save the file as UserInput.java (nothing else will do!!) and compile it using javac. Now run it. If you get any unexpected results check over the example code line by line and see where the error is.

Now lets dissect the code:

import java.io.*;

This is the first time you have met an import statement in your Java travels. Basically what import allows you to do is include all kinds of useful functions and methods provided by other people (or yourself). These are stored in other java programs or libraries. In this case you are importing the Java Input Output library. This library is provided with the Java SDK and will be installed.

public class UserInput {

public static void main(String [] args) throws IOExeption {

You already know what most of this code does apart from the IOException at the end. What this does is tell the Java system that something could go wrong in regards to I/O and to ready itself for such a situation. The main thing to remember is if using java.io.* is to ensure you include a throws IOException in your code.

BufferedReader in = new BufferedReader(new InputStreamReader(System.in));

This is an important part of the program.It creates a new BufferedReader object called in and tells it to read data from the standard input, in this case (and most others) the keyboard. Again don't worry too much about the syntax just remember how to use it at this stage.

String name = "";

This is another key piece of the program and also a key piece of java. This line creates a variable, a String variable to be more precise. A variable is a place in your computers memory where you can store surprisingly enough variable information, or in other words information that can be changed. A String variable therefore can hold a String. A String is a line of text for example "the cat sat on the mat" is an example of a String variable. In this case it is called name and is set to initially hold nothing (or "").

System.out.println("Enter your name: ");
System.out.flush();

The first line shouldn't be a problem. The second empties the buffer so that no garbage is  left in it to give you unexpected results.

name = in.readLine();

This line is probably the MOST important in the program. Basically it reads from the keyboard using the readLine() method and stores the result in name (the String variable we created and set to ""). Notice how the readLine function is called. It belongs to the BufferedReader class of which 'in' is an instance we created above.

System.out.println("Thank you. " + name);

This line prints the results of the program to the screen, notice how the statement prints the contents of the name variable not "name" itself. If I had wanted to print "name" to the screen I would have put it between speechmarks. Therefore no speechmarks means 'content of' if you like.

Finishing off

I'm afraid thats all for this time. Next time I am going to cover variable types (might be useful) and commenting. If in the meantime you have any problems you can contact me at my email address and I will try to answer your questions.

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