Data Input Stream Example in Java

Introduction

Data Input Stream is a classic Java console program that demonstrates the concept with complete source code and sample output. Java I/O reads and writes bytes and characters from files, streams and the console.

This tutorial walks through the program line by line, explains how the logic works, and highlights best practices you can apply in your own code.

Definition

A DataInputStream lets an application read primitive Java data types from an underlying input stream in a machine-independent way. The DataInputStream class enables you to read Java primitives from InputStream’s instead of only bytes.

Syntax

DataInputStream Variable_name = new DataInputStream(new FileInputStream("File_Location"));

Data Input Stream Example Program

import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
public class DataInputStreamDemo {
	public static void main(String[] args) throws IOException {
		InputStream in = null;
		DataInputStream ins = null;
		try{
			in = new FileInputStream("c:\\newfile.txt");// Assuming contents in the file named newfile.txt as "She sells sea shells on the sea shore"
			ins = new DataInputStream(in);
			int length = ins.available();
			byte[] bar = new byte[length];
			ins.readFully(bar);
			for (byte b:bar){
				char c = (char)b; 
				System.out.print(c);
			}
		}catch(Exception e){
			e.printStackTrace();
		}finally{
			if(in!=null)
            in.close();
			if(ins!=null)
            ins.close();
		}
	}
}

Sample Output

She sells sea shells on the sea shore

When to use

Use this data input stream example when learning or revising core Java syntax.

How it works

1. Execution begins in the main method — the JVM calls this method when you run the class.

2. import java.io.DataInputStream; imports a class used later in the program.

3. import java.io.FileInputStream; imports a class used later in the program.

4. import java.io.IOException; imports a class used later in the program.

5. import java.io.InputStream; imports a class used later in the program.

6. InputStream in = null; updates a variable used in the calculation or output.

7. DataInputStream ins = null; updates a variable used in the calculation or output.

8. A println / print call writes text to the console — part of the sample output below.

Best Practices

• Use meaningful variable and class names that describe their purpose.
• Compile and run the program locally — modify values to see how output changes.
• Read compiler errors carefully; they usually point to the exact line to fix.

Common Mistakes

• Copying code without understanding each line — practice by changing one statement at a time.
• Mismatching the public class name and the .java filename.
• Forgetting semicolons at the end of statements.