How to Use I/O Streams in Java

No matter which programming language one chooses, performing input and output operations are the core knowledge that one definitely needs to posses. From disk files, devices, other programs to memory arrays, a stream can represent a...

Method 1 of 4:

Using Byte and Character Streams

Byte streams handle input and output of raw binary data, byte by byte. Raw binary data is the type of data that hasn't been processed yet, bunch of ones and zeroes.

Character streams handle and translate input and output of character data, character by character. Translation, in this case, means that character streams automatically transform character format from and to the local character set.

How to Use I/O Streams in Java Picture 1

Create a text file. Give it an arbitrary name and write something in it, such as I love wikiHow!. In this article, we will name it file.txt.
How to Use I/O Streams in Java Picture 2
Create a main method. You can add throws IOException declaration to the method signature to avoid adding the catch block to the try-with-resources block.
```
public static void main(String[] args) { } 
```
How to Use I/O Streams in Java Picture 3
Create a try-with-resources block. Try-with-resources block will automatically close streams for us.
```
public static void main(String[] args) { try () { } } 
```
How to Use I/O Streams in Java Picture 4
Create FileInputStream or FileReader in the block statement. In the constructor of the created input stream, specify the name of the text file previously created. In this article, we called it file.txt.
```
public static void main(String[] args) { try (FileInputStream in = new FileInputStream("file.txt")) { } } 
```
1. The former is a byte stream, the latter is a character stream.
How to Use I/O Streams in Java Picture 5
Create FileOutputStream or FileWriter in the block statement. In the constructor of the created output stream, specify another arbitrary text file name. In this article, we will name it file-copy.txt.
```
public static void main(String[] args) { try ( FileInputStream in = new FileInputStream("file.txt"); FileOutputStream out = new FileOutputStream("file-copy.txt") ) { } } 
```
1. If you created FileInputStream, you need to create FileOutputStream. The same goes for the FileReader and FileWriter.

How to Use I/O Streams in Java Picture 6

Create int variable. This variable will be used for temporary storage of read byte or character.

public static void main(String[] args) { try ( FileInputStream in = new FileInputStream("file.txt"); FileOutputStream out = new FileOutputStream("file-copy.txt") ) { int data; } }

How to Use I/O Streams in Java Picture 7
Read data from input stream. Create a while loop in which the data is read into the previously created int variable until it reads the number -1. In other words, it reads data from the file until it reaches the end of the file.
```
public static void main(String[] args) { try ( FileInputStream in = new FileInputStream("file.txt"); FileOutputStream out = new FileOutputStream("file-copy.txt") ) { int data; while ((data = in.read()) != -1) { } } } 
```

How to Use I/O Streams in Java Picture 8

Write data to the output stream. In the body of the while loop, write the read data to the output stream.

public static void main(String[] args) { try ( FileInputStream in = new FileInputStream("file.txt"); FileOutputStream out = new FileOutputStream("file-copy.txt") ) { int data; while ((data = in.read()) != -1) { out.write(data); } } }

How to Use I/O Streams in Java Picture 9

Catch and handle IOException. Add a catch block to the try-with-resources block, catch IOException and, in case of an error, print the stack trace to the console.

public static void main(String[] args) { try ( FileInputStream in = new FileInputStream("file.txt"); FileOutputStream out = new FileOutputStream("file-copy.txt") ) { int data; while ((data = in.read()) != -1) { out.write(data); } } catch (IOException e) { e.printStackTrace(); } }

How to Use I/O Streams in Java Picture 10

Run the program. Contents of the file.txt are copied to the file-copy.txt which, if it doesn't exist yet, is created.

Method 2 of 4:

Using Buffered Streams

Buffered streams optimize input and output data. Buffer streams are more efficient than byte and character streams as they read and write from a buffer that is handled by Java platform rather than the underlying operating system. Most common usage of buffered streams is reading a textual file, line by line.

How to Use I/O Streams in Java Picture 11

Create a text file. Give it an arbitrary name and write something in it, such as I love wikiHow!. In this article, we will name it file.txt.
How to Use I/O Streams in Java Picture 12
Create a main method. You can add throws IOException declaration to the method signature to avoid adding the catch block to the try-with-resources block.
```
public static void main(String[] args) { } 
```
How to Use I/O Streams in Java Picture 13
Create a try-with-resources block. Try-with-resources block will automatically close streams for us.
```
public static void main(String[] args) { try () { } } 
```
How to Use I/O Streams in Java Picture 14
Create BufferedReader in the block statement. In the constructor of the created input stream, create a FileReader and specify the name of the text file previously created inside its constructor. In this article, we called it file.txt.
```
public static void main(String[] args) { try (BufferedReader in = new BufferedReader(new FileReader("file.txt"))) { } } 
```
How to Use I/O Streams in Java Picture 15
Create BufferedWriter in the block statement. In the constructor of the created output stream, create a FileWriter and specify another arbitrary text file name in its constructor. In this article, we will name it file-copy.txt.
```
public static void main(String[] args) { try ( BufferedReader in = new BufferedReader(new FileReader("file.txt")); BufferedWriter out = new BufferedWriter(new FileWriter("file-copy.txt")) ) { } } 
```

How to Use I/O Streams in Java Picture 16

Create String variable. This variable will be used for temporary storage of read lines.

public static void main(String[] args) { try ( BufferedReader in = new BufferedReader(new FileReader("file.txt")); BufferedWriter out = new BufferedWriter(new FileWriter("file-copy.txt")) ) { String line; } }

How to Use I/O Streams in Java Picture 17

Read lines from input stream. Create a while loop in which the lines are read into the previously created String variable until it reads null. In other words, it reads data from the file until it reaches the end of the file.

public static void main(String[] args) { try ( BufferedReader in = new BufferedReader(new FileReader("file.txt")); BufferedWriter out = new BufferedWriter(new FileWriter("file-copy.txt")) ) { String line; while ((line = in.readLine()) != null) { } } }

How to Use I/O Streams in Java Picture 18

Write lines to the output stream with line separator. In the body of the while loop, write the read lines to the output stream and append the line separator at the end of each line. BufferedReader reads lines, but omits the line separator.

public static void main(String[] args) { try ( BufferedReader in = new BufferedReader(new FileReader("file.txt")); BufferedWriter out = new BufferedWriter(new FileWriter("file-copy.txt")) ) { String line; while ((line = in.readLine()) != null) { out.write(line + System.lineSeparator()); } } }

How to Use I/O Streams in Java Picture 19

Catch and handle IOException. Add a catch block to the try-with-resources block, catch IOException and, in case of an error, print the stack trace to the console.

public static void main(String[] args) { try ( BufferedReader in = new BufferedReader(new FileReader("file.txt")); BufferedWriter out = new BufferedWriter(new FileWriter("file-copy.txt")) ) { String line; while ((line = in.readLine()) != null) { out.write(line + System.lineSeparator()); } } catch (IOException e) { e.printStackTrace(); } }

How to Use I/O Streams in Java Picture 20

Run the program. Contents of the file.txt are copied to the file-copy.txt which, if it doesn't exist yet, is created.

Method 3 of 4:

Using Data Streams

Data streams handle binary input and output of primitive data types and Strings. Data streams make it very easy to read and write boolean, char, byte, short, int, long, float, double and String values. Most common usage of data streams is in network applications (e.g. instant messengers).

How to Use I/O Streams in Java Picture 21
Create a main method. You can add throws IOException declaration to the method signature to avoid adding the catch block to the try-with-resources block.
```
public static void main(String[] args) { } 
```
How to Use I/O Streams in Java Picture 22
Create a try-with-resources block. Try-with-resources block will automatically close streams for us.
```
public static void main(String[] args) { try () { } } 
```
How to Use I/O Streams in Java Picture 23
Create DataOutputStream in the block statement. In the constructor of the created input stream, create FileOutputStream and specify an arbitrary file name inside its constructor. In this article, we will name it file.txt.
```
public static void main(String[] args) { try (DataOutputStream out = new DataOutputStream(new FileOutputStream("file.txt"))) { } } 
```
How to Use I/O Streams in Java Picture 24
Create DataInputStream in the block statement. In the constructor of the created input stream, create a FileInputStream and specify file name from the previous step inside its constructor. In this article, we named it file.txt.
```
public static void main(String[] args) { try ( DataOutputStream out = new DataOutputStream(new FileOutputStream("file.txt")); DataInputStream in = new DataInputStream(new FileInputStream("file.txt")) ) { } } 
```

How to Use I/O Streams in Java Picture 25

Write some data to the output stream. In the body of the try-with-resources block, write String, boolean, int and other primitive data to the output stream.

public static void main(String[] args) { try ( DataOutputStream out = new DataOutputStream(new FileOutputStream("file.txt")); DataInputStream in = new DataInputStream(new FileInputStream("file.txt")) ) { out.writeUTF("wikiHow is a great place to learn"); out.writeBoolean(true); out.writeInt(10430); out.writeDouble(20.9d); out.writeFloat(23.10f); } }

How to Use I/O Streams in Java Picture 26

Read data from the input stream and print it. Read the data in the same order as it has been written and print it to the console.

public static void main(String[] args) { try ( DataOutputStream out = new DataOutputStream(new FileOutputStream("file.txt")); DataInputStream in = new DataInputStream(new FileInputStream("file.txt")) ) { out.writeUTF("wikiHow is a great place to learn"); out.writeBoolean(true); out.writeInt(10430); out.writeDouble(20.9d); out.writeFloat(23.10f); System.out.println(in.readUTF()); System.out.println(in.readBoolean()); System.out.println(in.readInt()); System.out.println(in.readDouble()); System.out.println(in.readFloat()); } }

How to Use I/O Streams in Java Picture 27

Catch and handle IOException. Add a catch block to the try-with-resources block, catch IOException and, in case of an error, print the stack trace to the console.

public static void main(String[] args) { try ( DataOutputStream out = new DataOutputStream(new FileOutputStream("file.txt")); DataInputStream in = new DataInputStream(new FileInputStream("file.txt")) ) { out.writeUTF("wikiHow is a great place to learn"); out.writeBoolean(true); out.writeInt(10430); out.writeDouble(20.9d); out.writeFloat(23.10f); System.out.println(in.readUTF()); System.out.println(in.readBoolean()); System.out.println(in.readInt()); System.out.println(in.readDouble()); System.out.println(in.readFloat()); } catch (IOException e) { e.printStackTrace(); } }

How to Use I/O Streams in Java Picture 28
Run the program. Data is written to the file.txt and then read and printed to the console.
```
wikiHow is a great place to learn true 10430 20.9 23.1 
```

Method 4 of 4:

Using Object Streams

Object streams handle binary input and output of Java objects. Like data streams, object streams make it very easy to read and write primitive data types and Strings, but also any object that implements Serializable interface. Most common usage of object streams is in network applications where both server and client are written in Java.

How to Use I/O Streams in Java Picture 29
Create a serializable class. Create a class that implements Serializable interface. Name the class however you'd like, but in this article we will name it WikiHowian.
```
public class WikiHowian implements Serializable { } 
```
How to Use I/O Streams in Java Picture 30
Create a few private (serializable) variables. Since WikiHowian class represents a person, we will create two String variables for first and last name and an int variable for age.
```
public class WikiHowian implements Serializable { private String firstName, lastName; private int age; } 
```

How to Use I/O Streams in Java Picture 31

Create a constructor. The constructor will contain firstName, secondName and age parameters, corresponding to the private variable types.

public class WikiHowian implements Serializable { private String firstName, lastName; private int age; public WikiHowian(String firstName, String lastName, int age) { this.firstName = firstName; this.lastName = lastName; this.age = age; } }

How to Use I/O Streams in Java Picture 32

Override toString method. Overriding toString will, later on, allow us to print the object to the console easily.

public class WikiHowian implements Serializable { private String firstName, lastName; private int age; public WikiHowian(String firstName, String lastName, int age) { this.firstName = firstName; this.lastName = lastName; this.age = age; } @Override public String toString() { return firstName + " " + lastName + ", " + age; } }

How to Use I/O Streams in Java Picture 33

Create a main method. You can add throws IOException, ClassNotFoundException declaration to the method signature to avoid adding the catch block to the try-with-resources block.

public class WikiHowian implements Serializable { private String firstName, lastName; private int age; public WikiHowian(String firstName, String lastName, int age) { this.firstName = firstName; this.lastName = lastName; this.age = age; } @Override public String toString() { return firstName + " " + lastName + ", " + age; } public static void main(String[] args) { } }

How to Use I/O Streams in Java Picture 34

Create a try-with-resources block. Try-with-resources block will automatically close streams for us.

public class WikiHowian implements Serializable { private String firstName, lastName; private int age; public WikiHowian(String firstName, String lastName, int age) { this.firstName = firstName; this.lastName = lastName; this.age = age; } @Override public String toString() { return firstName + " " + lastName + ", " + age; } public static void main(String[] args) { try () { } } }

How to Use I/O Streams in Java Picture 35

Create ObjectOutputStream in the block statement. In the constructor of the created input stream, create FileOutputStream and specify an arbitrary file name inside its constructor. In this article, we will name it file.txt.

public class WikiHowian implements Serializable { private String firstName, lastName; private int age; public WikiHowian(String firstName, String lastName, int age) { this.firstName = firstName; this.lastName = lastName; this.age = age; } @Override public String toString() { return firstName + " " + lastName + ", " + age; } public static void main(String[] args) { try (ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("file.txt"))) { } } }

How to Use I/O Streams in Java Picture 36
Create ObjectInputStream in the block statement. In the constructor of the created input stream, create a FileInputStream and specify file name from the previous step inside its constructor. In this article, we named it file.txt.
```
public class WikiHowian implements Serializable { 
5 stars4 stars3 stars2 stars1 star5 ★ | 1 Vote
filestringnewtxt
Kareem WintersUpdate 05 March 2020
```
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