Course Java Syntax Zero - Lecture: Nuances of working with a conditional statement

1. Sequence of `if` statements

Sometimes a program needs to perform many different actions depending on the value of a variable or the value of an expression.

Let's say our task is something like this:

If the temperature is greater than 20 degrees, then put on a shirt
If the temperature is greater than 10 degrees and less than (or equal to) 20, then put on a sweater
If the temperature is greater than 0 degrees and less than (or equal to) 10, then put on a raincoat
If the temperature is less than 0 degrees, then put on a coat.

Here's how this can be represented in code:

int temperature = 9;

if (temperature > 20)
   System.out.println("put on a shirt");
else // Here the temperature is less than (or equal to) 20
{
   if (temperature > 10)
      System.out.println("put on a sweater");
   else // Here the temperature is less than (or equal to) 10
   {
      if (temperature > 0)
         System.out.println("put on a raincoat");
      else // Here the temperature is less than 0
         System.out.println("put on a coat");
   }
}

If-else statements can be nested within one another. This makes it possible to implement rather complex logic in a program.

But the above example is also interesting in that we can make the code a little simpler by omitting the curly braces:

int temperature = 9;

if (temperature > 20)
   System.out.println("put on a shirt");
else // Here the temperature is less than (or equal to) 20
   if (temperature > 10)
      System.out.println("put on a sweater");
   else // Here the temperature is less than (or equal to) 10
      if (temperature > 0)
         System.out.println("put on a raincoat");
      else // Here the temperature is less than 0
         System.out.println("put on a coat");

However, programmers usually write this construct a little differently:

int temperature = 9;

if (temperature > 20)
   System.out.println("put on a shirt");
else if (temperature > 10) // Here the temperature is less than (or equal to) 20
   System.out.println("put on a sweater");
else if (temperature > 0) // Here the temperature is less than (or equal to) 10
   System.out.println("put on a raincoat");
else // Here the temperature is less than 0
   System.out.println("put on a coat");

All three of these examples are equivalent.

2. Nuances of the `else` block

An important point:

If don't use curly braces in an if-else construct, then the else refers to the closest previous if.

Example:

Our code How will it work

int age = 65;

if (age < 60)
   if (age > 20)
      System.out.println("You must work");
else
   System.out.println("You don't have to work");

int age = 65;

if (age < 60)
{
   if (age > 20)
     System.out.println("You must work");
   else
     System.out.println("You don't have to work");
}

If you look at the code on the left, it seems that the screen output will be "You don't have to work". But that isn't the case. In reality, the else block and the "You don't have to work" statement are associated with the second (the closer) if statement.

In the code on the right, the associated if and else are highlighted in red. Additionally, the curly braces are placed unambiguously, clearly showing what actions will be performed. Is the string You don't have to work never displayed when age is greater than 60?

3. Example of using an `if-else` statement

Since we explored the if-else statement so well, let's give an example:

import java.util.Scanner;
public class Solution {
   public static void main(String[] args)
   {
     Scanner console = new Scanner(System.in); // Create a Scanner object
     int a = console.nextInt(); // Read the first number from the keyboard
     int b = console.nextInt(); // Read the second number from the keyboard
     if (a < b)                   // If a is less than b
       System.out.println(a);     // we display a
     else                         // otherwise
       System.out.println(b);     // we display b
   }
}

Displaying the minimum of two numbers

Comments (7)

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Timurlan Level 3, Russian Federation

2 August 2023

That's cool

Abe Level 13, los angeles, United States

15 January 2023

The example and the explanation under section 2 "Nuances of the else block" make no sense at all? I tried running both codes and got no output so what gives? what was supposed to be the output and why??

Gummy C Level 11, United States of America, United States

12 December 2022

if (age < 18){ if (age >= 6) System.out.println("Off to school with you, my child"); }else System.out.println("Your college class starts soon"); } So, just want to make sure I am understanding this bit of code. Because age =5, it will run the second if statement, and check to see if age is greater than 5. Since it is not, it doesn't return anything. The else is only associated with the first "if" statement. The else will only run, if the first "if" statement is false. Am I right about that? Thank you so much for answering

Anonymous#222 Level 3, Canada

23 November 2022

Nuances of working with a conditional statement

1. Sequence of if statements

2. Nuances of the else block

3. Example of using an if-else statement

1. Sequence of `if` statements

2. Nuances of the `else` block

3. Example of using an `if-else` statement