Add two numbers

This tutorial will demonstrate how to read from the input console (console line) to answer the prompts. The prompts will need to be a integer value to add the two inputs together.

I am using the InputStreamReader to convert the (console) into a stream, which into converted with a BufferedReader to get the whole line and not just one character/number.

The code

// just import the BufferedReader and inputstream reader
class addtwonumbers
       public static void main(String[] args)
              // reader (e.g. the input from the console)
              InputStreamReader ISR = new InputStreamReader(;       
              // buffer the console reader
              BufferedReader BR = new BufferedReader(ISR);                     
              // the default values for the two numbers
              int val1 = 0;
              int val2 = 0;
                     // output the question.
                     System.out.print("Enter first number : ");
                     // read in the console intput one line (BR.readLine) and then convert to a integer
                     val1 = Integer.parseInt(BR.readLine());
                     System.out.print("Enter second number : ");
                     val2 = Integer.parseInt(BR.readLine());
              catch (Exception ex)
                     // if the input was a string.
              // output the answer of adding both of the values together
              System.out.println("Answer = " + (val1 + val2));

save that as, because of course java is very picky about the class name to the java file, because Java creates a class of the same name as the class which in-turn is what the java virtual machine uses to execute.

Once compiled (javac and executed (java addtwonumbers) the output will be

Enter first number : 30
Enter second number : 23
Answer = 53

Read/Write Files

To read in from and file and also output to a file, java uses streams to “talk” to the files. These streams allow for communicating with different stream conversion tools, the object tool within this tutorial is the DataInputStream which “talks” to the FileInputStream.

I have attached the code within a zip file with the required input file as well.

Below is the code

class javareadfile
       public static void main(String args[])
              String fileName = "country.txt";//input file
              String outFileName = "sqljavacountry.txt";//output file
                     // file input stream, basically a pointer to the stream of the input file
                     FileInputStream fStream = new FileInputStream(fileName);
                     // file output stream, basically a pointer to the stream for outputing data
                     FileOutputStream fOutStream = new FileOutputStream(outFileName);
                     // the input/output data streams that connect to the above streams
                     DataInputStream dInput = new DataInputStream(fStream);
                     DataOutputStream dOutput = new DataOutputStream(fOutStream);
                     // whilst there is data available in the input stream
                     while (dInput.available() !=0)
                            String in = dInput.readLine();// read a line from the input file
                            // output a stream of data to the output file
                            dOutput.writeBytes("insert into country(place) values (\""+in+"\");\n");
                     //close the two files.
              catch (Exception e)// incase of any errors
                     System.err.println("There was a error : " + e.toString());

If you save this as and also create a countrys.txt file with what ever text you like, e.g.

United Kingdom
United States

Once you have compiled the program (javac -deprecation, may have to use -deprecation if using java virtual machine 1.5 over 1.4) and execute the program (java javareadfile), it will look for the file countrys.txt within the same directory as the program executable and also create outcountrys.txt within the same directory (it will write over the file if there is one present). Then within the while loop it will read the input file line by line and output to the screen what has been read and also output to the output file.

Of course to finish off to close down the files and return back to the console.

Hello world ! classic

This is the classic hello world tutorial for java, to get the java compiler and also the run-time environment you will need to goto the Java (Sun). The compiler (javac) compiles into java byte code, which means that this code is able to run on any OS with the java run-time environment (aka virtual machine).

If you save this

public class helloworld
	public static void main(String[] args)
		System.out.println("Hello world");


and then from the command line


this will create the helloworld.class which is the java byte code, to run the byte code.

java helloworld

and hopefully there will be

Hello world

on the console.