[java] How to use readline() method in Java?

I am beginner in Java, and I was reading the topic of giving values to variables through the readLine() method from the keyboard. The program for that is given in the book is as follows:

import java.io.DataInputStream
class Reading
{
    public static void main(String args[])
    {
        DataInputStream in = new DataInputStream(System.in);
        int intnumber=0;
        float floatnumber=0.0f;
        try {
            system.out.println("enter an integer: ");
            intnumber = Integer.parseInt(in.readline());

            system.out.println("enter a float number: ");
            floatnumber = Float.valueOf(in.readline()).floatvalue();
        }

        // Rest of code

I want to ask the following questions:

1. What is done in the following statement?

   DataInputStream in = new DataInputStream(System.in);
   

   If in is an object of DataInputStream then what is new and what do the statement on the right-hand side of above statement do?

2. Why have different methods been used for putting the integer value into intnumber and float value into floatnumber?

This will explain it, I think...

import java.io.*;

class reading
{
    public static void  main(String args[]) throws IOException
    {
        float number;
        System.out.println("Enter a number");
        try
        {
            InputStreamReader in = new InputStreamReader(System.in);
            BufferedReader br = new BufferedReader(in);
            String a = br.readLine();
            number = Float.valueOf(a);
            int x = (int)number;

            System.out.println("Your input=" + number);
            System.out.println("Your input in integer terms is = " + x);
        }
        catch(Exception e){
        }
    }
}

In summary: I would be careful as to what code you copy. It is possible you are copying code which happens to work, rather than well chosen code.

In intnumber, parseInt is used and in floatnumber valueOf is used why so?

There is no good reason I can see. It's an inconsistent use of the APIs as you suspect.

Java is case sensitive, and there isn't any Readline() method. Perhaps you mean readLine().

DataInputStream.readLine() is deprecated in favour of using BufferedReader.readLine();

However, for your case, I would use the Scanner class.

Scanner sc = new Scanner(System.in);
int intNum = sc.nextInt();
float floatNum = sc.nextFloat();

If you want to know what a class does I suggest you have a quick look at the Javadoc.

Use BufferedReader and InputStreamReader classes.

BufferedReader buffer=new BufferedReader(new InputStreamReader(System.in));
String line=buffer.readLine();

Or use java.util.Scanner class methods.

Scanner scan=new Scanner(System.in);

A DataInputStream is just a decorator over an InputStream (which System.in is) which allows to read using more convenient methods.

As to the Float.valueOf(), well, that's curious because Float has .parseFloat() as well. Here the code grabs a Float with .valueOf() which it turns into the primitive float type using .floatValue(), which is unnecessary with Java 1.5+ due to auto unboxing.

And as other answers rightly say, these methods are obsolete anyway.