Java - InputStreamReader read() method

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Description

The Java InputStreamReader read() method reads characters from an input stream and returns them as integers. It is commonly used for reading text files or character streams. Returns -1 if the end of the stream (EOF) is reached.

Declaration

Following is the declaration for java.io.InputStreamReader.read() method −

public int read()

Parameters

NA

Return Value

The method returns the character read, or -1 if the end of the stream has been reached.

Exception

IOException − If an I/O error occurs

Example - Usage of InputStreamReader read() method

The following example shows the usage of Java InputStreamReader read() method.

InputStreamReaderDemo.java

package com.tutorialspoint;

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

public class InputStreamReaderDemo {
   public static void main(String[] args) throws IOException {
      FileInputStream fis = null;
      InputStreamReader isr = null;
      char c;
      int i;
      
      try {
         // new input stream reader is created 
         fis = new FileInputStream("test.txt");
         isr = new InputStreamReader(fis);
         
         // read till the end of the file
         while((i = isr.read())!=-1) {
         
            // int to character
            c = (char)i;
            
            // print char
            System.out.println("Character Read: "+c);
         }
         
      } catch (Exception e) {
         // print error
         e.printStackTrace();
      } finally {
         // closes the stream and releases resources associated
         if(fis!=null)
            fis.close();
         if(isr!=null)
            isr.close();
      }   
   }
}

Output(Assuming test.txt contains "ABCDE")

Let us compile and run the above program, this will produce the following result−

Character Read: A
Character Read: B
Character Read: C
Character Read: D
Character Read: E

Example - Reading One Character at a Time

The following example shows the usage of Java InputStreamReader read() method.

InputStreamReaderDemo.java

package com.tutorialspoint;

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

public class InputStreamReaderDemo {
   public static void main(String[] args) {
      try (InputStreamReader reader = new InputStreamReader(new FileInputStream("example.txt"))) {
         int data;
         while ((data = reader.read()) != -1) { // Read character by character
            System.out.print((char) data); // Convert integer to character and print
         }
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output(if example.txt contains "Hello")

Let us compile and run the above program, this will produce the following result−

Hello

Explanation

• Uses InputStreamReader to read text from "example.txt".

• Calls read() to read one character at a time.

• Converts the integer Unicode value into a character ((char) data).

• Stops reading when read() returns -1 (EOF reached).

Example - Using read() to Store Data Before Printing

The following example shows the usage of Java InputStreamReader read() method.

InputStreamReaderDemo.java

package com.tutorialspoint;

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

public class InputStreamReaderDemo {
   public static void main(String[] args) {
      try (InputStreamReader reader = new InputStreamReader(new FileInputStream("example.txt"))) {
         StringBuilder content = new StringBuilder();
         int data;

         while ((data = reader.read()) != -1) { // Read one character at a time
            content.append((char) data); // Store in StringBuilder instead of printing immediately
         }

         // Print entire content at once
         System.out.println("File Content:\n" + content);
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output(if example.txt contains "Hello World!")

Let us compile and run the above program, this will produce the following result−

File Content:
Hello World!

Explanation

Use StringBuilder When

• You need to process or modify the text before printing

• The file is large, and printing character-by-character is inefficient.

Don't use this approach when

• You need to print immediately (e.g., for real-time logs or a live feed).

• The file is too large to fit in memory (use buffered reading instead).