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Beginner: Introduction to Beginner Module

Why computer is dumb?

Scenario

We ask our sibling and computer to play Pushpa movie.

Sibling

  • Can play a movie
  • Does not need any instructions

Computer

  • Needs step by step instructions in detailed manner
  • Hence, computer is dumb.

Need of programming languages

Scenario: The coder is trying to communicate with the computer.

  • Examples of all languages they we know - Hindi, English, Telugu, Tamil, Marathi, Punjabi, Kannada, etc.
  • Computer cannot understand these languages. It can only understand 0s and 1s.
  • Since, we cannot learn to write instructions in binary language. We have learned programming languages like JAVA, C++, C#, Python, etc.
  • Now, we need a translator to translate our instructions. So, computer can understand the instructions.
  • Compiler helps us convert the code into machine understandable language.

Diagram to elaborate this:

IDE

Integrated Development Environment :

  • IDE - tool for developers for software editing, building, testing, and packaging in an easy-to-use application,
  • Since, we will not be doing these complicated things right now. We do not need any software installation required.

We will be using online ide throughout this module.

Scaler’s Online IDE: https://www.scaler.com/topics/java/online-java-compiler/

Importance of Syntax

I love to cook.

We can understand the meaning of this sentence.

I garden know don’t.

We cannot understand the meaning of this sentence.

The reason being the grammar is wrong.

Grammar :Rules of writing English.

Similarly, Rules of writing code : Syntax

Now, let us learn some rules and start writing our very first code.

Basic codes

public class Main {
    public static void main(String[] args) {
        System.out.print(100)
    }
}

The code which is already written, we can just ignore all those words. We will be learning about them in the upcoming sessions.

To get output in JAVA, we use:

 System.out.print(100)

Output:

 [CompilationError] Your code was terminated due to compilation error
Main.java:4: error: ';' expected

 System.out.print(100)

Rule 1 : Every statement should end with a semi-colon(;)

Correct the code and then run again.

 System.out.print(100);

Output:

100

Rule 2 : JAVA is Case Sensitive.

We can try one more example.

 system.out.print(5000);

Output

 [CompilationError] Your code was terminated due to compilation error
 Main.java:4: error: package system does not exist

 system.out.print(5000);
  • We can observe that something is wrong with “system” and see the difference between the two statements.
  • The only difference is that S is lowercase here.

Correct Method:

 System.out.print(5000);

Output:

5000

Rule 3 : In order to print text we use double quotes (" ")

Printing text in Output 

 System.out.print(Priyanshi);

On running it, we will get an error.

 Correct Way: System.out.print(“Priyanshi”);

Rule 4 : () , {}, “ ” → These All Should Be in Pairs

On removing one bracket from the code, it gives error. 

class Main {
    public static void main(String args[]) {
      // Your code goes here
}

Output:

[CompilationError] Your code was terminated due to compilation error
Main.java:error: reached end of file while parsing
 }

Rule 5 : For Comments, Use // And /* … */

Comments -> Statements which we want our compiler to ignore. Comments are of two types :

  1. Single Line Comments : To write a single line comment just add two forward slashes (//) in front of the statement.
// System.out.print("HI");

// This is a single line comment.

2. Multi Line Comments : In order to comment out multiple lines together, we add /* at the beginning and then */ to close the comment.

 /*
System.out.print("Hello");
This is a multi line comment.
*/

Rule 6 : print() and println()

Let’s try to print something like this:

Hello Guys!!

Welcome to Robin Dhole blog!

 System.out.print(“Hello Guys!!”);
 System.out.print(“Welcome to Robin Dhole blog!”);

Output:

Hello Guys!!Welcome to Robin Dhole blog!

This is not giving us the correct output.

Introduce : System.out.println();

 System.out.println(“Hello Guys!!”);
 System.out.println(“Welcome to Robin Dhole blog!”);

Output:

Hello Guys!!
Welcome to Scaler!

Rule 6

print -> Just type the output

println -> Type the output and press Enter[cursor goes to next line]

Summary

  1. end statements with a semicolon ( ; )
  2. JAVA is case sensitive. -> System, system are considered different
  3. In order to print text, we use double quotes ( " " )
  4. {}, (), " " → All of these are in pairs.
  5. Comments →
    1. Single-line comments start with two forward slashes ( // ). Any text between // and the end of the line is ignored by Java (will not be executed).
    2. Multi-line comments start with /* and ends with /. Any text between / and */ will be ignored by Java.
  6. System.out.print(); → Just type the output
  7. System.out.println(); → Just type the output and press Enter [cursor moves to the next line]