Search⌘ K
AI Features
Home
Courses
Learn to Code: Java for Absolute Beginners

First Java Program

Explore the basics of Java programming by writing your first program that displays output and takes input from users. Understand how to use comments, variables, input methods like nextLine(), output commands like System.out.println(), and create simple interactive applications. Practice by creating a personalized greeting and a story program using multiple inputs.

We'll cover the following...

Problem solving with Java

The basic tools for understanding the flow and the results of simple programs are execution sheetsAn execution sheet is a manual way for observing and updating the values of the variables at each step of the execution of a program. and flowchartsA flowchart is a diagram that helps understand the sequence of instructions in a program having decision.. However, they become complicated when we have problems with a large number of decisions. Therefore, we provide executable embedded code widgets to observe the program output by executing it.

We can run a program as many times as we want, to try out different inputs of variables. We can also edit these programs to observe the result of a change in a value or logic for our learning.

In Java, we use nextLine() for input (to read a value from the user) and System.out.println() for print (to display a value on the screen as output).

Hello World

It’s time to write our first program in Java, which will simply display the message “Hello World!” on the screen.

This is the code widget that we’ll use to write our Java code. We may execute our Java program by clicking the “Run” button at the bottom of the widget:

Java
// First Java program to display Hello World
class Test
{
    public static void main(String args[]) 
    {
        System.out.print("Hello World!");
    }
}

Note: We can add non-executable text in a Java program by adding a double backslash sign (//) at the start of the text. This type of text is called a comment. We use comments to include descriptions in the program.

Explanation

  • Line 1: This is a comment because it starts with // (a double slash). It is only for the readers of this program. It describes the purpose and/or related matters of the program.

  • Line 2–3: These are used as a requirement by the language. It is the start of the first block of code. Every starting brace { has a corresponding closing brace }, as seen in line 8. We will be using these lines, as is, in almost every Java program.

  • Line 4–5: These are the start of the executable part of the program. Every executable Java program has a main, which serves as its entry/starting point. The starting brace { indicates the start of the second block of code. See the corresponding closing brace } in line 7.

  • Line 6: It is the only line that caused the program to give output. It corresponds to the purpose of the whole program. Every other line is in support of line 6. We use System.out. before print as a requirement by the language.

  • Line 7: This is the end of the main block of code. It corresponds to the opening brace in line 5.

  • Line 8: This is the end of the class block of code. It corresponds to the opening brace in line 3.

New line in the output

There are different ways of giving a line break in the output, as demonstrated in the following code:

Java
// First Java program to display the line breaks in different ways
class Test
{
    public static void main(String args[]) 
    {
        System.out.print("Single"); // The next output will be on the same line 
        System.out.print("Line\n");  // The next output will be on the next line due to new line symbol \n 
        System.out.print("Separate new line" + "\n"); // The new line symbol can be written separately
        System.out.println("Use of println for new line"); // The println adds a line break at the end
        System.out.print("It demonstrates the line break"); // This line is shown on a new line
    }
}

Explanation

  • Lines 6–7: The text of these lines is on the same line in the output. The \n symbol, termed as a new line character, causes the line break.
  • Line 8: This shows the use of \n as a separate text.
  • Line 9: This illustrates the use of println for giving a line break in the output, as demonstrated from the output of line 10.

Personalize messages with a variable

Let’s write another Java program that inputs the name of the user before displaying a greeting message. We use the variable, yourName, to store the input given by the user in Java.

A variable name can only contain letters (A–Z and a–z) and the underscore symbol (_). It may also contain digits (0–9), but the variable name can’t start with those. For example, Key_2 is a valid variable name but 2_key is not. Variable names are case-sensitive, meaning that name, Name, and NAME are three different variables.

The Test.java in the left pane of the following widget is the name of the program file. .java indicates that it’s a Java program. When we press the “Run” button to execute the program, it shows a black screen called the terminal, where we can input values and see the resulting output:

import java.util.Scanner;  // Import the Scanner class
class Test 
{
  public static void main(String[] args) 
  {
    Scanner myObj = new Scanner(System.in);  // Create a Scanner object
    System.out.print("Enter your name: " + '\n');
    String yourName = myObj.nextLine();  // Read user input
    System.out.print("Hello " + yourName + '\n');
    System.out.print("Welcome to Educative" + '\n');  // Output user input
  }
}
Take and display the input of name (variable)

The word exit at the end of the output indicates the completion of the program in the terminal.

Explanation

  • Line 1: The Scanner class is used to get user input, and it is found in the java.util package. That’s why we import the package.
  • Line 6: To use the Scanner class, we have to create an object. In our case, we are creating an object, myObj, of the Scanner class and using any of the available methods found in the Scanner class. Scanner(System.in) is used to read input from the terminal window.
  • Line 8: nextLine() reads a string value from the user.

Note: \n is an escape character in Java that is used to enter a new line in the output.

The code above displays the message, "Hello ", before the value of the name variable on the first line. The space after Hello is part of the label to keep a space before the value of name in the output. Then, it displays “Welcome to Educative” on the second line.

Java programming practice

Let’s practice writing the first Java program that takes multiple inputs from the user.

Tell a story

Let’s write a program that tells a story with information given by the user. The program should ask the user to enter their name, age, city, college, profession, and pet’s name.

We’ll need to provide user input in the box labeled “Enter the input below.” Therefore, when the solution is ready for execution, we can test it by providing the following information line by line in the input box on behalf of the user.

  • User’s name
  • User’s age
  • User’s city
  • User’s college
  • User’s profession
  • User’s pet’s name

Once we are done writing the program, we can execute by clicking the “Run” button. The program should display the prompts to enter an input on the terminal, and we can enter the required input. Remember to store the input and print it using print/println, where required. The program should display the following story, inserting the user’s input into the appropriate locations in the following text:

There once was a person named NAME who lived in CITY. At the age of AGE, NAME went to college at COLLEGE. NAME graduated and went to work as a PROFESSION. Then, NAME adopted an animal named PETNAME. They both lived happily ever after!

import java.util.Scanner;  // Import the Scanner class
class Test
{
    public static void main(String args[]) 
    {
        // Write you code here
    }
}
Take and display multiple inputs