How to Take Input in Java? (With Examples)

Introduction to using input in Java

An integral part of any program is to take inputs from its user. Oracle Corporation claims that Java is used on 3 billion devices all around the globe, and hence to fulfill all the user’s demands, it provides all the necessary means required to take input of any form.

In Computer Science, input refers to any data that is provided to the computer by any means. There are mainly three types of user inputs:

• Keyboard Interactions: User can provide various types of inputs to a program through the keyboard, which can be interpreted as letters, numbers, etc.
• Command Line Arguments: In order to run our program, we need to provide the instructions through the command line. These commands allow the JVM (Java Virtual Machine) to recognize the program, which it needs to compile into a byte file and later run for execution.
• Files: For systemized storage of all interrelated data, we all choose file storage. A File can be provided as user input to a program by specifying its location in the program or as user input, as shown below in the code snippet:

Our major focus in this article will be to dwell upon the inputs we can take from the keyboard/console. This mostly covers the primitive data types such as int, double, long, byte, etc.

Using Buffered Reader Class

This is the most primitive method (introduced in JDK 1.0) offered by Java for taking user inputs. The name tells about its main function, which is to provide a buffer for data. This buffer stores the input given by the user, which is transferred through the input stream.

It wraps the System.in in InputStreamReader, which is later wrapped under BufferedReader.

It can also read input from users through the command line.

Syntax

Example

Output

Advantages

1. It is the most efficient method for reading input.
2. It works better when we read files because of its large buffer size.
3. We can use it while working on multiple threads.
4. There is no ambiguity related to taking multiple inputs through the readLine() method.

Disadvantages

1. We may need to specify the buffer size (in bytes) even though the default size is itself very large. We can specify the buffer size in the BufferedReader constructor as follows:

2. It can only take string inputs. For other data types, we need to convert the String input to that data type using the corresponding parse function such as Integer.parseInt(), Double.parseDouble(), etc.
3. We need to import multiple libraries into our program to take input through the BufferedReader class.

Using Scanner Class

This is the most widely used method for taking inputs in a java program. It uses the Scanner class, which provides us with specific methods to parse the input given to the program using specific methods listed below. We can also read user input in the command line using the Scanner class.

Syntax

Example

Output

Advantages

1. Easy to implement and hence widely used.
2. Better compatibility with smaller data types, and it is generally the best option for Competitive Coding.
3. Provides convenient methods for parsing the primitive data types, which are easy to memorize (ex. nextInt(), nextFloat(), …) from the tokenized input.
4. Regular expressions can be used to find tokens. Reading methods are not synchronized.
5. Offers a much easier approach to reading records from a data file.

Disadvantages

1. It is slower as compared to the BufferedReader class.
2. It fails to perform efficiently for larger inputs as its buffer size is - 1KB char buffer, which is very small when compared to that of BufferedReader (8KB byte buffer).
3. It is not synchronous, and it does not deliver appropriate performance when we work with multiple threads.

Using Console Class

This method is usually used for inputting passwords. In addition, it can be used for reading password-like input without echoing the characters entered by the user. The format of the input string syntax can also be used (like System.out.printf()).

The console class has no buffer when reading from the system console, but it has a buffered output stream to write to the system console.

We need to add the java.io.Console library to implement the System.console() function.

Syntax

Example

Output

Advantages

1. It allows us to enter passwords into our system with security as it does not make the password visible while typing it.
2. We can use the format of strings to specify the input strings format.
3. The methods used by this class are synchronized.

Disadvantages

1. This method fails to work in interactive environments like IDEs where all the input is not given at once.
2. The method does not allow us to utilize shortcuts offered by popular compilers like Visual Studio Code and IntelliJ.

Example: Using Java Command-Line Arguments of the main() method

We can provide inputs to our program through the Command Prompt just the moment after we begin to execute our program.

Java programs are compiled and run by

Compile > javac filename.java 
Run > java filename

These inputs are to be added just after the filename in the run command. These inputs are dealt with by JVM (Java Virtual Machine). They are taken as strings and passed to the main function as its parameters.

Output:

Explanation:

The program demonstrates how to access and display command-line arguments passed to the Java program. The args parameter in the main() method holds the command-line arguments as an array of strings. The program prints the total number of arguments and displays each argument using a for-each loop.

Example 2: Get Integer Input From the User

Output:

Explanation:

The program prompts the user to enter an integer, reads the input using the Scanner class, and stores it in the number variable. Finally, it displays the entered integer.

Example 3: Get float, double and String Input

Output:

Explanation:

The program demonstrates reading different types of input from the user. It prompts the user to enter a float, a double, and a string. It uses the nextFloat() and nextDouble() methods to read the floating-point values, and nextLine() is used to consume the newline character before reading the string input. Finally, it displays the entered values.