Java Decision Making - if Statement

Decision making

Normally, the program is executed sequentially. In some situation in the programming the flow is not applicable to execute sequentially. In that case we need repeat some statements until certain condition is encountered.

Branching

When a program does not follow the sequential flow or the program breaks the sequential flow and jumps to another part of code, then it is called as branching.

Types of branching

1. Conditional :

if the branching proceeds as per the occurrence of condition or decision then it is known as conditional branching

2. Unconditional :

when branching is not based on a particular condition or decision then it is known as conditional branching.

Types of Unconditional branching

If statement

If statement is a simplest decision making statement. It is used to control the flow of execution of statements.

Syntax

if ( test - expression ) 
{ 
    // if block statements are executed when test-expression becomes true
    // write whatever you want
}

Flowchart of if statement

How if statement works?

• he compiler first evaluates the test expression then; control is transferred to the particular statement as the result of test expression.
• If test expression result is true, then executes the body of if statement otherwise it skips the body and goes to next statement.

Example : ATM login system for displaying balance of user

In below example we are taking input from user throw commandline argument as ATM PIN and checking the available balance

class IfStatement
{
    public static void main(String args[])
    {
      int PIN;
      int balance = 15000;
      PIN = Integer.parseInt(arg[0]);
		
      if (PIN == 1234)
      {
	System.out.println("Welcome user");
	System.out.println("Your balance is "+ balance);
      }
      System.out.println("\nThank you for login");
    }
}

Output

In above example we have taken input from user and condition is written as PIN == 1234.
The relational operator = = is used to compare two different values. If both values are equal then if block statement is executed.

But the statements outside the if block are by default executed.Thats why 'thank you for login is get printed'.

Types of If statement

There are 3 different types of if statement based on their need.

1. if-else statement
2. Nested if-else statement
3. else-if ladder