Conditional branching in Java

Beknazar

Mar 10·6 min read

Conditional branching is a logical part of the program. Based on the specific condition we can tell to program which way the program should go.

if <it's cold outside> then I will get my jacket
else I'm good with T-shirt 

The above example shows a simple version of conditional branching in plain language. <it's cold outside> this is a logical condition and it can be true or false. If it’s true then we will perform some action and if it’s false we can perform another action.

The logical condition can be stored in boolean type variable and can be used as part of the conditional branching statements(if-esle, ternary operator).

// class and main method is not displayed
boolean b = true;
if (b) {
   System.out.println("Java is great!");
}else {
   System.out.println("Python is great!");
}

in above the snippet we can see the simple if-else statement.

• The output of this program is Java is great!
• The if statement always takes boolean datatype as its condition, between the parenthesis. If the condition true if’s body will be executed and if it’s false else’s body will be executed.
• This code will always print Java is great! because we hardcoded the value of our boolean as true. Usually, we get boolean from some conditions (comparison, event, etc.).

Comparison Operators

Let’s talk about how we can get a logical boolean. One way to get it is by using comparison operators.

• == equal to operator. We can use this operator to compare primitive datatypes on equality. For objects, it will compare if two references are pointing to the same object or not(we will talk more in the future).
• != not equal to operator. Exactly same as equal, but works in reverse.
• > greater than operator. To compare if one number greater than another.
• >= greater than or equal to operator. To compare if one number greater or equal to another number.
• < less than
• <= less than or equal to

Using == to compare numbers on equality.

The output from the above program is Samsung. The not equal operator is the exact opposite of equal to operator. If numbers are not equal it will return true and if they are equal it will return false.

The greater than and less than operators are very straightforward. if you want to also check greater/less or equal you need add = after the operator. Like >= and <=

Logical Operators

Write a method that will accept one number argument. If number within a range 10–20 inclusive print Java otherwise, print Python.

Even though, above code works well for our requirement, it’s not the best way of achieving it. For this simple condition, we used two if-else statements. Now let’s see code using a logical operator.

Here we used the logical AND(&&) operator. The logical operators are super useful to connect boolean conditions into one. They help us to make our conditions clean and short. When using AND operator all conditions should be true then only the whole condition will be true.

• && logical AND operator
• || logical OR operator
• ! logical NOT operator

Write a mathod that will accept one number as an argument.
Assume numbers 7, 13, 99 are lucky numbers. If the number is lucky, print Jackpot! otherwise, print Not today!.

With the OR operator if at least one part true then the whole condition is true.

Logical NOT operator will reverse value of boolean.

boolean b = true;
boolean c = !b;
boolean d = !false;
System.out.println(b); // true
System.out.println(c); // false
System.out.println(d); // trueint money = 99;
if (!(money >= 100)) {
    System.out.println("It's not enough");
}

We can use logical NOT just in front of the boolean condition and it will reverse its value. Notice how we use parentheses. Parentheses clarify the meaning of a boolean expression. Also, they are useful when many conditions are used together to clarify and separate.

Multibranch if-else

Write a method that will accept one double number and will print a message based on this number:
- if the number within a range of 13.5–15.5 inclusive, print normal pressure
- if the number is less than 13.5 exclusives, print low pressure
- otherwise, print high pressure

public void printPressureMsg(double pressure) {
   if (pressure >= 13.5 && pressure <= 15.5) {
      System.out.println("normal pressure");
   }else if (pressure < 13.5) {
      System.out.println("low pressure");
   }else {
      System.out.println("high pressure");
   }
}

As you can see here we can connect if statements into one statement. Only one of them will be executed and if all do not match else statement will be executed. Else part is optional. It’s always better to have multibranch if-else than having multiple if statements separately.

write a method that accepts one number and will print a message based on
- if the number is even print Fizz
- if the number is odd print Buzz
- if the number is odd and divisible by 5 evenly print FizzBuzz

public void fizzBuzz(int num) {
   if (num % 2 == 0) {
      System.out.println("Fizz");
   } else if (num % 2 == 1) {
      System.out.println("Buzz"); 
   } else if (num % 2 == 1 && num % 5 == 0) {
      System.out.println("FizzBuzz");
   }
}

It seems like a correct method but there a defect in the code. For most of the number it will work fine but for example, for 15 it will print Buzz but it should print FizzBuzz.

Order of the if/else if is very important. We discussed that only one statement will be executed even though a few of them can true. So in our case num % 2 == 1 is true and num % 2 == 1 && num % 5 == 0 is also true. And correct one is the second one but the first one is first by order so it will always catch this condition and get executed.

public void fizzBuzz(int num) {
   if (num % 2 == 0) {
      System.out.println("Fizz");
   } else if (num % 2 == 1 && num % 5 == 0) {
      System.out.println("FizzBuzz"); 
   } else if (num % 2 == 1) {
      System.out.println("Buzz");
   }
}

This is the correct version.

This article is part of the series of articles to learn Java programming language from Tech Lead Academy:1. Introduction to programming 
2. OS, File, and File System
3. Working with terminal 
4. Welcome to Java Programming Language
5. Variables and Primitives in Java
6. Methods with Java
7. Java Math Operators and special operators
8. Conditional branching in Java
9. Switch statement in Java
10. Ternary operator in Java
11. Enum in Java
12. String class and its methods in Java
13. Loops in Java
14. Access modifiers in Java
15. Static keyword in Java
16. The final keyword in Java
17. Class and Object in Java
18. Object Oriented Programming in Java
19. OOP: Encapsulation in Java
20. Inheritance in Java
21. Abstraction in Java
22. Polymorphism in Java
23. Overriding vs Overloading in Java
24. OOP Design Principles in Java
25. Array in Java
26. Data Structures with Java
27. Collection framework in Java
28. ArrayList in Java
29. Set in Java
30. Map in Java
31. LocalDate in Java
32. Exception in Java
33. IO in Java
34. Design Patterns
35. Generics in Java
36. Multithreading in java
37. JUnit
38. Big O Notation for coding interviews
39. Top 17 Java coding interview questions for SDET