Java - InputStreamReader Class

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Introduction

The Java InputStreamReader class is a bridge from byte streams to character streams.It reads bytes and decodes them into characters using a specified charset.

Class declaration

Following is the declaration for Java.io.InputStreamReader class −

public class InputStreamReader
   extends Reader

Field

Following are the fields for Java.io.InputStreamReader class −

• protected Object lock − This is the object used to synchronize operations on this stream.

Class constructors

Class methods

Methods inherited

This class inherits methods from the following classes −

• Java.io.Reader
• Java.io.Object

Example - Using close() with InputStreamReader (Automatic Closure with Try-With-Resources)

The following example shows the usage of Java InputStreamReader close() 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);
         }
         // No need to manually close, try-with-resources handles it
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output(if example.txt contains "JavaProgramming")

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

JavaProgramming

Explanation

• Uses InputStreamReader, which reads characters from a file.

• Reads one character at a time using read().

• Uses try-with-resources, which automatically calls close() at the end.

Example - Getting Default Encoding of InputStreamReader

The following example shows the usage of Java InputStreamReader getEncoding() 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"))) {
         System.out.println("Encoding used: " + reader.getEncoding());
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

Encoding used: UTF8

Explanation

• Creates an InputStreamReader with default encoding.

• Calls getEncoding() to print the encoding used.

• The encoding depends on the JVM default (e.g., "UTF8" or "Cp1252" on Windows).

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).