Input Stream Reader Example in Java

Introduction

Input Stream Reader 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

The InputStreamReader class converts an InputStream to a Reader. It has constructors that support specifying the character encoding to use. This is used with FileInputStream.

Syntax

	FileInputStream Variable_name_1 = new FileInputStream("File_location");
	InputStreamReader Variable_name_2 = new InputStreamReader(Variable_name_1);

Input Stream Reader Example Program

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;

public class InputStreamReaderExample {
	public static void main(String[] args) throws IOException {
		FileInputStream fistr = null;
		InputStreamReader istrr =null;
		char c;
		int i;
		try {
			fistr = new FileInputStream("C:/newfile.txt");// Assuming a text file newfile.txt with content "JAVA"
			istrr = new InputStreamReader(fistr);
			while((i=istrr.read())!=-1){
				c=(char)i;
				System.out.println("Character Read: "+c);
			}
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			if(fistr!=null)
			fistr.close();
			if(istrr!=null)
            istrr.close();
		}   
	}
}

Sample Output

Character Read:J
Character Read:A
Character Read:V
Character Read:A

When to use

Use this input stream reader 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.FileInputStream; imports a class used later in the program.

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

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

5. FileInputStream fistr = null; updates a variable used in the calculation or output.

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

7. fistr = new FileInputStream("C:/newfile.txt");// Assuming a text file newfile.txt with content "JAVA" updates a variable used in the calculation or output.

8. A loop repeats the block until its condition becomes false.

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.