In every programming language, there is a need for a repeated use of a set of statements which together perform a certain task. Instead of repeating these statements everytime, we instead group these into certain methods and call these methods to perform the tasks. In Java, these methods are written within classes which are further contained within packages. In this unit, we will learn what are packages and how we can use them to read inputs from the user and print the output.
In Java, a package is a group of related classes, sub-packages, etc. Packages can be conceptually compared to different folders (also called directories) on your computer. The package consists of re-usable code, which eliminates the need for the programmer to write the same code several times. Java provides a number of built-in packages. For example,
java.lang
java.util
java.net, etc.
To utilize a package or a specific class, we need to use import keyword.
To import a complete package with all its classes, we can use the syntax given below .
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import java.util.*; |
Using an asterisk (*) imports a whole package along with all the classes contained within.
Java also gives us the option of importing a specific class from a package based on our requirements. The below statement imports the Scanner class from the java.util package.
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import java.util.Scanner; |
You can think of a package's folder structure like this:
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|___ java |___ util |___Scanner.java |
All the Java files have an extension of .java. The Scanner.java file consists of the Scanner class. Here, the Scanner.java file is located in the util folder and the util is located in the java folder.
The Scanner class in the package java.util is used to read user input.
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import java.util.Scanner; class Main { public static void main(String[] args) { Scanner input = new Scanner(System.in); String username = input.nextLine();
System.out.println(username); input.close(); // closing Scanner object } } |
Input & Output
Here, calling new Scanner() will return an object and it is assigned to the variable named input The System.in parameter is used to read input from the standard input (i.e., keyboard). nextLine() method is used to read a String value till the end of line.
Calling input.close(), closes the Scanner object input. We cannot read the user input once it is closed. It is a good programming practice to explicitly close the Scanner using the close() method once you are done using it.
The Scanner object provides various methods that allow us to read inputs of different data types.
Following are the methods, used to read different types of inputs from the user:
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Method |
Description |
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nextInt() |
Reads an int value |
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nextLong() |
Reads a long value |
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nextFloat() |
Reads a float value |
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nextBoolean() |
Reads a boolean value |
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next() |
Reads a String value only until a space(" ") is encountered |
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nextLine() |
Reads a String value till the end of line |
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nextDouble() |
Reads a double value |
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nextShort() |
Reads a short value |
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nextByte() |
Reads a byte value |
Scanner class does not have a specific method to read character input from the user. To read a char, we use next().charAt(0)
The next() method reads the input as a string and charAt(0) (string method) returns the first character of the string. We will learn more about String Methods later in the course.
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import java.util.Scanner; class Main { public static void main(String[] args) { Scanner input = new Scanner(System.in); char ch = input.next().charAt(0);
System.out.println(ch); input.close(); // closing Scanner object } } |
R
R
A single Scanner object can be used for reading multiple inputs of various data types from the user.
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import java.util.Scanner; class Main { public static void main(String[] args) { Scanner input = new Scanner(System.in); String username = input.nextLine(); int age = input.nextInt();
System.out.println(username); System.out.println(age); input.close(); // closing Scanner object } } |
Ajay
20
Ajay
20
Java can read multiple inputs from a single line, in contrast to Python, which reads the entire line as a single input.
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import java.util.Scanner; class Main { public static void main(String[] args) { Scanner input = new Scanner(System.in); int firstValue = input.nextInt(); int secondValue = input.nextInt();
System.out.println(firstValue); System.out.println(secondValue); input.close(); // closing Scanner object } } |
34 56
34
56
As we learned, nextInt() reads an integer value only until a space(" ") or new line is encountered.
So far, we have learned to accept input from the user, let's take a look at different methods available to print the output to the console.
print()
println()
The System class in java.lang package is used to access the print() and the println() methods.
The java.lang package is the default package in Java and will be imported by default. Therefore, there is no need to import this package explicitly.
The print() accepts a value as a parameter and prints text on the console. It prints the result in the same line.
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class Main { public static void main(String[] args) { String greetings = "Hello"; String name = "Rahul"; System.out.print(greetings); System.out.print(name); } } |
HelloRahul
Comparison with Python
The println() accepts a value as a parameter and prints text on the console. It prints the result in the new line.
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class Main { public static void main(String[] args) { String greetings = "Hello"; String name = "Rahul"; System.out.println(greetings); System.out.println(name); } } |
Hello
Rahul
import keyword is used to import packages in Java.
Scanner class is used to read input from the user and it provides different methods for taking different input types from the user.
print() and the println() methods are used to print output to the console.
print() function prints in the same line whereas, println() function goes to new line after printing