The basic if statement

The simplest conditional statement is the simple if statement. An if statement defines a code block (the if block) and a conditional (or Boolean) statement. The code block executes once only if the condition evaluates to true. If it’s not true, Java skips over the if block and executes the first statement following the if block. The schematic to the right illustrates the flow of execution of a simple if statement.

As an example, let’s consider a program that prompts the user to enter a decimal value. If the value entered is less than zero, the program will display the message “You entered a negative value.” Before terminating, the program will display the message “Done.” Here’s what the code would look like:

import java.util.Scanner;

public class Conditionals1

{

public static void main(String[] args)

{

Scanner s = new Scanner(System.in);

System.out.print(“Enter a number: “);

double num = s.nextDouble();

// execute block only if num is negative

if (num < 0.0)

{

System.out.println(“You entered a negative value.”);

}

// the following statement will execute regardless of the // value entered

System.out.println(“Done.”);

}

}